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C/C++ Interface For SQLite Version 3
This page defined the C-language interface to SQLite.
This is not a tutorial. These
pages are designed to be precise, not easy to read.
For a tutorial introduction see
SQLite In 3 Minutes Or Less
and/or
the Introduction To The SQLite C/C++ Interface
.
This page contains all C-language interface information
in a single HTML file. The same information is also
available broken out into
lots of small pages
for easier viewing, if you prefer.
This document is created by a script which scans comments
in the source code files.
Experimental And Deprecated Interfaces
SQLite interfaces can be subdivided into three categories:
- Stable
- Experimental
- Deprecated
Stable interfaces will be maintained indefinitely in a backwards
compatible way. An application that uses only stable interfaces
should always be able to relink against a newer version of SQLite
without any changes.
Experimental interfaces are subject to change.
Applications that use experimental interfaces
may need to be modified when upgrading to a newer SQLite release, though
this is rare.
When new interfaces are added to SQLite, they generally begin
as experimental interfaces. After an interface has been in use for
a while and the developers are confident that the design of the interface
is sound and worthy of long-term support, the interface is marked
as stable.
Deprecated interfaces have been superceded by better methods of
accomplishing the same thing and should be avoided in new applications.
Deprecated interfaces continue to be supported for the sake of
backwards compatibility. At some point in the future, it is possible
that deprecated interfaces may be removed.
Key points:
- Experimental interfaces are subject to change and/or removal
at any time.
- Deprecated interfaces should not be used in new code and might
be removed in some future release.
Objects:
Note: Objects marked with "exp
"
are experimental
and objects marked with
"(obs)
" are deprecated
.
sqlite3
sqlite3_backup
sqlite3_blob
sqlite3_context
sqlite3_file
sqlite3_index_info
sqlite3_int64
sqlite3_uint64
|
sqlite_int64
sqlite_uint64
sqlite3_io_methods
sqlite3_mem_methods
sqlite3_module
sqlite3_mutex
sqlite3_mutex_methods
sqlite3_pcache
|
sqlite3_pcache_methods2
sqlite3_pcache_page
sqlite3_stmt
sqlite3_temp_directory
sqlite3_value
sqlite3_vfs
sqlite3_vtab
sqlite3_vtab_cursor
|
Constants:
Note: Constants marked with "(exp)
"
are experimental
and constants marked with
"(obs)
" are deprecated
Functions:
Note: Functions marked with "(exp)
"
are experimental
and functions marked with
(obs)
are deprecated
.
Maximum xShmLock index
#define SQLITE_SHM_NLOCK 8
The xShmLock method on sqlite3_io_methods
may use values
between 0 and this upper bound as its "offset" argument.
The SQLite core will never attempt to acquire or release a
lock outside of this range
Virtual Table Configuration Options
#define SQLITE_VTAB_CONSTRAINT_SUPPORT 1
These macros define the various options to the
sqlite3_vtab_config()
interface that virtual table
implementations
can use to customize and optimize their behavior.
SQLITE_VTAB_CONSTRAINT_SUPPORT
Calls of the form
sqlite3_vtab_config
(db,SQLITE_VTAB_CONSTRAINT_SUPPORT,X) are supported,
where X is an integer. If X is zero, then the virtual table
whose
xCreate
or xConnect
method invoked sqlite3_vtab_config()
does not
support constraints. In this configuration (which is the default) if
a call to the xUpdate
method returns SQLITE_CONSTRAINT
, then the entire
statement is rolled back as if OR ABORT
had been
specified as part of the users SQL statement, regardless of the actual
ON CONFLICT mode specified. If X is non-zero, then the virtual table implementation guarantees
that if xUpdate
returns SQLITE_CONSTRAINT
, it will do so before
any modifications to internal or persistent data structures have been made.
If the ON CONFLICT
mode is ABORT, FAIL, IGNORE or ROLLBACK, SQLite
is able to roll back a statement or database transaction, and abandon
or continue processing the current SQL statement as appropriate.
If the ON CONFLICT mode is REPLACE and the xUpdate
method returns
SQLITE_CONSTRAINT
, SQLite handles this as if the ON CONFLICT mode
had been ABORT.
Virtual table implementations that are required to handle OR REPLACE
must do so within the xUpdate
method. If a call to the
sqlite3_vtab_on_conflict()
function indicates that the current ON
CONFLICT policy is REPLACE, the virtual table implementation should
silently replace the appropriate rows within the xUpdate callback and
return SQLITE_OK. Or, if this is not possible, it may return
SQLITE_CONSTRAINT, in which case SQLite falls back to OR ABORT
constraint handling.
Online Backup Object
typedef struct sqlite3_backup sqlite3_backup;
The sqlite3_backup object records state information about an ongoing
online backup operation. The sqlite3_backup object is created by
a call to sqlite3_backup_init()
and is destroyed by a call to
sqlite3_backup_finish()
.
See Also: Using the SQLite Online Backup API
SQL Function Context Object
typedef struct sqlite3_context sqlite3_context;
The context in which an SQL function executes is stored in an
sqlite3_context object. A pointer to an sqlite3_context object
is always first parameter to application-defined SQL functions
.
The application-defined SQL function implementation will pass this
pointer through into calls to sqlite3_result()
,
sqlite3_aggregate_context()
, sqlite3_user_data()
,
sqlite3_context_db_handle()
, sqlite3_get_auxdata()
,
and/or sqlite3_set_auxdata()
.
OS Interface Open File Handle
typedef struct sqlite3_file sqlite3_file;
struct sqlite3_file {
const struct sqlite3_io_methods *pMethods; /* Methods for an open file */
};
An sqlite3_file
object represents an open file in the
OS interface layer
. Individual OS interface
implementations will
want to subclass this object by appending additional fields
for their own use. The pMethods entry is a pointer to an
sqlite3_io_methods
object that defines methods for performing
I/O operations on the open file.
Virtual Table Indexing Information
struct sqlite3_index_info {
/* Inputs */
int nConstraint; /* Number of entries in aConstraint */
struct sqlite3_index_constraint {
int iColumn; /* Column on left-hand side of constraint */
unsigned char op; /* Constraint operator */
unsigned char usable; /* True if this constraint is usable */
int iTermOffset; /* Used internally - xBestIndex should ignore */
} *aConstraint; /* Table of WHERE clause constraints */
int nOrderBy; /* Number of terms in the ORDER BY clause */
struct sqlite3_index_orderby {
int iColumn; /* Column number */
unsigned char desc; /* True for DESC. False for ASC. */
} *aOrderBy; /* The ORDER BY clause */
/* Outputs */
struct sqlite3_index_constraint_usage {
int argvIndex; /* if >0, constraint is part of argv to xFilter */
unsigned char omit; /* Do not code a test for this constraint */
} *aConstraintUsage;
int idxNum; /* Number used to identify the index */
char *idxStr; /* String, possibly obtained from sqlite3_malloc */
int needToFreeIdxStr; /* Free idxStr using sqlite3_free() if true */
int orderByConsumed; /* True if output is already ordered */
double estimatedCost; /* Estimated cost of using this index */
};
The sqlite3_index_info structure and its substructures is used as part
of the virtual table
interface to
pass information into and receive the reply from the xBestIndex
method of a virtual table module
. The fields under **Inputs** are the
inputs to xBestIndex and are read-only. xBestIndex inserts its
results into the **Outputs** fields.
The aConstraint[] array records WHERE clause constraints of the form:
column OP expr where OP is =, <, <=, >, or >=. The particular operator is
stored in aConstraint[].op using one of the
SQLITE_INDEX_CONSTRAINT_ values
.
The index of the column is stored in
aConstraint[].iColumn. aConstraint[].usable is TRUE if the
expr on the right-hand side can be evaluated (and thus the constraint
is usable) and false if it cannot.
The optimizer automatically inverts terms of the form "expr OP column"
and makes other simplifications to the WHERE clause in an attempt to
get as many WHERE clause terms into the form shown above as possible.
The aConstraint[] array only reports WHERE clause terms that are
relevant to the particular virtual table being queried.
Information about the ORDER BY clause is stored in aOrderBy[].
Each term of aOrderBy records a column of the ORDER BY clause.
The xBestIndex
method must fill aConstraintUsage[] with information
about what parameters to pass to xFilter. If argvIndex>0 then
the right-hand side of the corresponding aConstraint[] is evaluated
and becomes the argvIndex-th entry in argv. If aConstraintUsage[].omit
is true, then the constraint is assumed to be fully handled by the
virtual table and is not checked again by SQLite.
The idxNum and idxPtr values are recorded and passed into the
xFilter
method.
sqlite3_free()
is used to free idxPtr if and only if
needToFreeIdxPtr is true.
The orderByConsumed means that output from xFilter
/xNext
will occur in
the correct order to satisfy the ORDER BY clause so that no separate
sorting step is required.
The estimatedCost value is an estimate of the cost of doing the
particular lookup. A full scan of a table with N entries should have
a cost of N. A binary search of a table of N entries should have a
cost of approximately log(N).
OS Interface File Virtual Methods Object
typedef struct sqlite3_io_methods sqlite3_io_methods;
struct sqlite3_io_methods {
int iVersion;
int (*xClose)(sqlite3_file*);
int (*xRead)(sqlite3_file*, void*, int iAmt, sqlite3_int64 iOfst);
int (*xWrite)(sqlite3_file*, const void*, int iAmt, sqlite3_int64 iOfst);
int (*xTruncate)(sqlite3_file*, sqlite3_int64 size);
int (*xSync)(sqlite3_file*, int flags);
int (*xFileSize)(sqlite3_file*, sqlite3_int64 *pSize);
int (*xLock)(sqlite3_file*, int);
int (*xUnlock)(sqlite3_file*, int);
int (*xCheckReservedLock)(sqlite3_file*, int *pResOut);
int (*xFileControl)(sqlite3_file*, int op, void *pArg);
int (*xSectorSize)(sqlite3_file*);
int (*xDeviceCharacteristics)(sqlite3_file*);
/* Methods above are valid for version 1 */
int (*xShmMap)(sqlite3_file*, int iPg, int pgsz, int, void volatile**);
int (*xShmLock)(sqlite3_file*, int offset, int n, int flags);
void (*xShmBarrier)(sqlite3_file*);
int (*xShmUnmap)(sqlite3_file*, int deleteFlag);
/* Methods above are valid for version 2 */
/* Additional methods may be added in future releases */
};
Every file opened by the sqlite3_vfs.xOpen
method populates an
sqlite3_file
object (or, more commonly, a subclass of the
sqlite3_file
object) with a pointer to an instance of this object.
This object defines the methods used to perform various operations
against the open file represented by the sqlite3_file
object.
If the sqlite3_vfs.xOpen
method sets the sqlite3_file.pMethods element
to a non-NULL pointer, then the sqlite3_io_methods.xClose method
may be invoked even if the sqlite3_vfs.xOpen
reported that it failed. The
only way to prevent a call to xClose following a failed sqlite3_vfs.xOpen
is for the sqlite3_vfs.xOpen
to set the sqlite3_file.pMethods element
to NULL.
The flags argument to xSync may be one of SQLITE_SYNC_NORMAL
or
SQLITE_SYNC_FULL
. The first choice is the normal fsync().
The second choice is a Mac OS X style fullsync. The SQLITE_SYNC_DATAONLY
flag may be ORed in to indicate that only the data of the file
and not its inode needs to be synced.
The integer values to xLock() and xUnlock() are one of
- SQLITE_LOCK_NONE
,
- SQLITE_LOCK_SHARED
,
- SQLITE_LOCK_RESERVED
,
- SQLITE_LOCK_PENDING
, or
- SQLITE_LOCK_EXCLUSIVE
.
xLock() increases the lock. xUnlock() decreases the lock.
The xCheckReservedLock() method checks whether any database connection,
either in this process or in some other process, is holding a RESERVED,
PENDING, or EXCLUSIVE lock on the file. It returns true
if such a lock exists and false otherwise.
The xFileControl() method is a generic interface that allows custom
VFS implementations to directly control an open file using the
sqlite3_file_control()
interface. The second "op" argument is an
integer opcode. The third argument is a generic pointer intended to
point to a structure that may contain arguments or space in which to
write return values. Potential uses for xFileControl() might be
functions to enable blocking locks with timeouts, to change the
locking strategy (for example to use dot-file locks), to inquire
about the status of a lock, or to break stale locks. The SQLite
core reserves all opcodes less than 100 for its own use.
A list of opcodes
less than 100 is available.
Applications that define a custom xFileControl method should use opcodes
greater than 100 to avoid conflicts. VFS implementations should
return SQLITE_NOTFOUND
for file control opcodes that they do not
recognize.
The xSectorSize() method returns the sector size of the
device that underlies the file. The sector size is the
minimum write that can be performed without disturbing
other bytes in the file. The xDeviceCharacteristics()
method returns a bit vector describing behaviors of the
underlying device:
- SQLITE_IOCAP_ATOMIC
- SQLITE_IOCAP_ATOMIC512
- SQLITE_IOCAP_ATOMIC1K
- SQLITE_IOCAP_ATOMIC2K
- SQLITE_IOCAP_ATOMIC4K
- SQLITE_IOCAP_ATOMIC8K
- SQLITE_IOCAP_ATOMIC16K
- SQLITE_IOCAP_ATOMIC32K
- SQLITE_IOCAP_ATOMIC64K
- SQLITE_IOCAP_SAFE_APPEND
- SQLITE_IOCAP_SEQUENTIAL
The SQLITE_IOCAP_ATOMIC property means that all writes of
any size are atomic. The SQLITE_IOCAP_ATOMICnnn values
mean that writes of blocks that are nnn bytes in size and
are aligned to an address which is an integer multiple of
nnn are atomic. The SQLITE_IOCAP_SAFE_APPEND value means
that when data is appended to a file, the data is appended
first then the size of the file is extended, never the other
way around. The SQLITE_IOCAP_SEQUENTIAL property means that
information is written to disk in the same order as calls
to xWrite().
If xRead() returns SQLITE_IOERR_SHORT_READ it must also fill
in the unread portions of the buffer with zeros. A VFS that
fails to zero-fill short reads might seem to work. However,
failure to zero-fill short reads will eventually lead to
database corruption.
Memory Allocation Routines
typedef struct sqlite3_mem_methods sqlite3_mem_methods;
struct sqlite3_mem_methods {
void *(*xMalloc)(int); /* Memory allocation function */
void (*xFree)(void*); /* Free a prior allocation */
void *(*xRealloc)(void*,int); /* Resize an allocation */
int (*xSize)(void*); /* Return the size of an allocation */
int (*xRoundup)(int); /* Round up request size to allocation size */
int (*xInit)(void*); /* Initialize the memory allocator */
void (*xShutdown)(void*); /* Deinitialize the memory allocator */
void *pAppData; /* Argument to xInit() and xShutdown() */
};
An instance of this object defines the interface between SQLite
and low-level memory allocation routines.
This object is used in only one place in the SQLite interface.
A pointer to an instance of this object is the argument to
sqlite3_config()
when the configuration option is
SQLITE_CONFIG_MALLOC
or SQLITE_CONFIG_GETMALLOC
.
By creating an instance of this object
and passing it to sqlite3_config
(SQLITE_CONFIG_MALLOC
)
during configuration, an application can specify an alternative
memory allocation subsystem for SQLite to use for all of its
dynamic memory needs.
Note that SQLite comes with several built-in memory allocators
that are perfectly adequate for the overwhelming majority of applications
and that this object is only useful to a tiny minority of applications
with specialized memory allocation requirements. This object is
also used during testing of SQLite in order to specify an alternative
memory allocator that simulates memory out-of-memory conditions in
order to verify that SQLite recovers gracefully from such
conditions.
The xMalloc, xRealloc, and xFree methods must work like the
malloc(), realloc() and free() functions from the standard C library.
SQLite guarantees that the second argument to
xRealloc is always a value returned by a prior call to xRoundup.
xSize should return the allocated size of a memory allocation
previously obtained from xMalloc or xRealloc. The allocated size
is always at least as big as the requested size but may be larger.
The xRoundup method returns what would be the allocated size of
a memory allocation given a particular requested size. Most memory
allocators round up memory allocations at least to the next multiple
of 8. Some allocators round up to a larger multiple or to a power of 2.
Every memory allocation request coming in through sqlite3_malloc()
or sqlite3_realloc()
first calls xRoundup. If xRoundup returns 0,
that causes the corresponding memory allocation to fail.
The xInit method initializes the memory allocator. (For example,
it might allocate any require mutexes or initialize internal data
structures. The xShutdown method is invoked (indirectly) by
sqlite3_shutdown()
and should deallocate any resources acquired
by xInit. The pAppData pointer is used as the only parameter to
xInit and xShutdown.
SQLite holds the SQLITE_MUTEX_STATIC_MASTER
mutex when it invokes
the xInit method, so the xInit method need not be threadsafe. The
xShutdown method is only called from sqlite3_shutdown()
so it does
not need to be threadsafe either. For all other methods, SQLite
holds the SQLITE_MUTEX_STATIC_MEM
mutex as long as the
SQLITE_CONFIG_MEMSTATUS
configuration option is turned on (which
it is by default) and so the methods are automatically serialized.
However, if SQLITE_CONFIG_MEMSTATUS
is disabled, then the other
methods must be threadsafe or else make their own arrangements for
serialization.
SQLite will never invoke xInit() more than once without an intervening
call to xShutdown().
Mutex Handle
typedef struct sqlite3_mutex sqlite3_mutex;
The mutex module within SQLite defines sqlite3_mutex
to be an
abstract type for a mutex object. The SQLite core never looks
at the internal representation of an sqlite3_mutex
. It only
deals with pointers to the sqlite3_mutex
object.
Mutexes are created using sqlite3_mutex_alloc()
.
Mutex Methods Object
typedef struct sqlite3_mutex_methods sqlite3_mutex_methods;
struct sqlite3_mutex_methods {
int (*xMutexInit)(void);
int (*xMutexEnd)(void);
sqlite3_mutex *(*xMutexAlloc)(int);
void (*xMutexFree)(sqlite3_mutex *);
void (*xMutexEnter)(sqlite3_mutex *);
int (*xMutexTry)(sqlite3_mutex *);
void (*xMutexLeave)(sqlite3_mutex *);
int (*xMutexHeld)(sqlite3_mutex *);
int (*xMutexNotheld)(sqlite3_mutex *);
};
An instance of this structure defines the low-level routines
used to allocate and use mutexes.
Usually, the default mutex implementations provided by SQLite are
sufficient, however the user has the option of substituting a custom
implementation for specialized deployments or systems for which SQLite
does not provide a suitable implementation. In this case, the user
creates and populates an instance of this structure to pass
to sqlite3_config() along with the SQLITE_CONFIG_MUTEX
option.
Additionally, an instance of this structure can be used as an
output variable when querying the system for the current mutex
implementation, using the SQLITE_CONFIG_GETMUTEX
option.
The xMutexInit method defined by this structure is invoked as
part of system initialization by the sqlite3_initialize() function.
The xMutexInit routine is called by SQLite exactly once for each
effective call to sqlite3_initialize()
.
The xMutexEnd method defined by this structure is invoked as
part of system shutdown by the sqlite3_shutdown() function. The
implementation of this method is expected to release all outstanding
resources obtained by the mutex methods implementation, especially
those obtained by the xMutexInit method. The xMutexEnd()
interface is invoked exactly once for each call to sqlite3_shutdown()
.
The remaining seven methods defined by this structure (xMutexAlloc,
xMutexFree, xMutexEnter, xMutexTry, xMutexLeave, xMutexHeld and
xMutexNotheld) implement the following interfaces (respectively):
- sqlite3_mutex_alloc()
- sqlite3_mutex_free()
- sqlite3_mutex_enter()
- sqlite3_mutex_try()
- sqlite3_mutex_leave()
- sqlite3_mutex_held()
- sqlite3_mutex_notheld()
The only difference is that the public sqlite3_XXX functions enumerated
above silently ignore any invocations that pass a NULL pointer instead
of a valid mutex handle. The implementations of the methods defined
by this structure are not required to handle this case, the results
of passing a NULL pointer instead of a valid mutex handle are undefined
(i.e. it is acceptable to provide an implementation that segfaults if
it is passed a NULL pointer).
The xMutexInit() method must be threadsafe. It must be harmless to
invoke xMutexInit() multiple times within the same process and without
intervening calls to xMutexEnd(). Second and subsequent calls to
xMutexInit() must be no-ops.
xMutexInit() must not use SQLite memory allocation (sqlite3_malloc()
and its associates). Similarly, xMutexAlloc() must not use SQLite memory
allocation for a static mutex. However xMutexAlloc() may use SQLite
memory allocation for a fast or recursive mutex.
SQLite will invoke the xMutexEnd() method when sqlite3_shutdown()
is
called, but only if the prior call to xMutexInit returned SQLITE_OK.
If xMutexInit fails in any way, it is expected to clean up after itself
prior to returning.
Custom Page Cache Object
typedef struct sqlite3_pcache sqlite3_pcache;
The sqlite3_pcache type is opaque. It is implemented by
the pluggable module. The SQLite core has no knowledge of
its size or internal structure and never deals with the
sqlite3_pcache object except by holding and passing pointers
to the object.
See sqlite3_pcache_methods2
for additional information.
Custom Page Cache Object
typedef struct sqlite3_pcache_page sqlite3_pcache_page;
struct sqlite3_pcache_page {
void *pBuf; /* The content of the page */
void *pExtra; /* Extra information associated with the page */
};
The sqlite3_pcache_page object represents a single page in the
page cache. The page cache will allocate instances of this
object. Various methods of the page cache use pointers to instances
of this object as parameters or as their return value.
See sqlite3_pcache_methods2
for additional information.
Name Of The Folder Holding Temporary Files
SQLITE_EXTERN char *sqlite3_temp_directory;
If this global variable is made to point to a string which is
the name of a folder (a.k.a. directory), then all temporary files
created by SQLite when using a built-in VFS
will be placed in that directory. If this variable
is a NULL pointer, then SQLite performs a search for an appropriate
temporary file directory.
It is not safe to read or modify this variable in more than one
thread at a time. It is not safe to read or modify this variable
if a database connection
is being used at the same time in a separate
thread.
It is intended that this variable be set once
as part of process initialization and before any SQLite interface
routines have been called and that this variable remain unchanged
thereafter.
The temp_store_directory pragma
may modify this variable and cause
it to point to memory obtained from sqlite3_malloc
. Furthermore,
the temp_store_directory pragma
always assumes that any string
that this variable points to is held in memory obtained from
sqlite3_malloc
and the pragma may attempt to free that memory
using sqlite3_free
.
Hence, if this variable is modified directly, either it should be
made NULL or made to point to memory obtained from sqlite3_malloc
or else the use of the temp_store_directory pragma
should be avoided.
OS Interface Object
typedef struct sqlite3_vfs sqlite3_vfs;
typedef void (*sqlite3_syscall_ptr)(void);
struct sqlite3_vfs {
int iVersion; /* Structure version number (currently 3) */
int szOsFile; /* Size of subclassed sqlite3_file */
int mxPathname; /* Maximum file pathname length */
sqlite3_vfs *pNext; /* Next registered VFS */
const char *zName; /* Name of this virtual file system */
void *pAppData; /* Pointer to application-specific data */
int (*xOpen)(sqlite3_vfs*, const char *zName, sqlite3_file*,
int flags, int *pOutFlags);
int (*xDelete)(sqlite3_vfs*, const char *zName, int syncDir);
int (*xAccess)(sqlite3_vfs*, const char *zName, int flags, int *pResOut);
int (*xFullPathname)(sqlite3_vfs*, const char *zName, int nOut, char *zOut);
void *(*xDlOpen)(sqlite3_vfs*, const char *zFilename);
void (*xDlError)(sqlite3_vfs*, int nByte, char *zErrMsg);
void (*(*xDlSym)(sqlite3_vfs*,void*, const char *zSymbol))(void);
void (*xDlClose)(sqlite3_vfs*, void*);
int (*xRandomness)(sqlite3_vfs*, int nByte, char *zOut);
int (*xSleep)(sqlite3_vfs*, int microseconds);
int (*xCurrentTime)(sqlite3_vfs*, double*);
int (*xGetLastError)(sqlite3_vfs*, int, char *);
/*
** The methods above are in version 1 of the sqlite_vfs object
** definition. Those that follow are added in version 2 or later
*/
int (*xCurrentTimeInt64)(sqlite3_vfs*, sqlite3_int64*);
/*
** The methods above are in versions 1 and 2 of the sqlite_vfs object.
** Those below are for version 3 and greater.
*/
int (*xSetSystemCall)(sqlite3_vfs*, const char *zName, sqlite3_syscall_ptr);
sqlite3_syscall_ptr (*xGetSystemCall)(sqlite3_vfs*, const char *zName);
const char *(*xNextSystemCall)(sqlite3_vfs*, const char *zName);
/*
** The methods above are in versions 1 through 3 of the sqlite_vfs object.
** New fields may be appended in figure versions. The iVersion
** value will increment whenever this happens.
*/
};
An instance of the sqlite3_vfs object defines the interface between
the SQLite core and the underlying operating system. The "vfs"
in the name of the object stands for "virtual file system". See
the VFS documentation
for further information.
The value of the iVersion field is initially 1 but may be larger in
future versions of SQLite. Additional fields may be appended to this
object when the iVersion value is increased. Note that the structure
of the sqlite3_vfs object changes in the transaction between
SQLite version 3.5.9 and 3.6.0 and yet the iVersion field was not
modified.
The szOsFile field is the size of the subclassed sqlite3_file
structure used by this VFS. mxPathname is the maximum length of
a pathname in this VFS.
Registered sqlite3_vfs objects are kept on a linked list formed by
the pNext pointer. The sqlite3_vfs_register()
and sqlite3_vfs_unregister()
interfaces manage this list
in a thread-safe way. The sqlite3_vfs_find()
interface
searches the list. Neither the application code nor the VFS
implementation should use the pNext pointer.
The pNext field is the only field in the sqlite3_vfs
structure that SQLite will ever modify. SQLite will only access
or modify this field while holding a particular static mutex.
The application should never modify anything within the sqlite3_vfs
object once the object has been registered.
The zName field holds the name of the VFS module. The name must
be unique across all VFS modules.
SQLite guarantees that the zFilename parameter to xOpen
is either a NULL pointer or string obtained
from xFullPathname() with an optional suffix added.
If a suffix is added to the zFilename parameter, it will
consist of a single "-" character followed by no more than
11 alphanumeric and/or "-" characters.
SQLite further guarantees that
the string will be valid and unchanged until xClose() is
called. Because of the previous sentence,
the sqlite3_file
can safely store a pointer to the
filename if it needs to remember the filename for some reason.
If the zFilename parameter to xOpen is a NULL pointer then xOpen
must invent its own temporary name for the file. Whenever the
xFilename parameter is NULL it will also be the case that the
flags parameter will include SQLITE_OPEN_DELETEONCLOSE
.
The flags argument to xOpen() includes all bits set in
the flags argument to sqlite3_open_v2()
. Or if sqlite3_open()
or sqlite3_open16()
is used, then flags includes at least
SQLITE_OPEN_READWRITE
| SQLITE_OPEN_CREATE
.
If xOpen() opens a file read-only then it sets *pOutFlags to
include SQLITE_OPEN_READONLY
. Other bits in *pOutFlags may be set.
SQLite will also add one of the following flags to the xOpen()
call, depending on the object being opened:
- SQLITE_OPEN_MAIN_DB
- SQLITE_OPEN_MAIN_JOURNAL
- SQLITE_OPEN_TEMP_DB
- SQLITE_OPEN_TEMP_JOURNAL
- SQLITE_OPEN_TRANSIENT_DB
- SQLITE_OPEN_SUBJOURNAL
- SQLITE_OPEN_MASTER_JOURNAL
- SQLITE_OPEN_WAL
The file I/O implementation can use the object type flags to
change the way it deals with files. For example, an application
that does not care about crash recovery or rollback might make
the open of a journal file a no-op. Writes to this journal would
also be no-ops, and any attempt to read the journal would return
SQLITE_IOERR. Or the implementation might recognize that a database
file will be doing page-aligned sector reads and writes in a random
order and set up its I/O subsystem accordingly.
SQLite might also add one of the following flags to the xOpen method:
- SQLITE_OPEN_DELETEONCLOSE
- SQLITE_OPEN_EXCLUSIVE
The SQLITE_OPEN_DELETEONCLOSE
flag means the file should be
deleted when it is closed. The SQLITE_OPEN_DELETEONCLOSE
will be set for TEMP databases and their journals, transient
databases, and subjournals.
The SQLITE_OPEN_EXCLUSIVE
flag is always used in conjunction
with the SQLITE_OPEN_CREATE
flag, which are both directly
analogous to the O_EXCL and O_CREAT flags of the POSIX open()
API. The SQLITE_OPEN_EXCLUSIVE flag, when paired with the
SQLITE_OPEN_CREATE, is used to indicate that file should always
be created, and that it is an error if it already exists.
It is not
used to indicate the file should be opened
for exclusive access.
At least szOsFile bytes of memory are allocated by SQLite
to hold the sqlite3_file
structure passed as the third
argument to xOpen. The xOpen method does not have to
allocate the structure; it should just fill it in. Note that
the xOpen method must set the sqlite3_file.pMethods to either
a valid sqlite3_io_methods
object or to NULL. xOpen must do
this even if the open fails. SQLite expects that the sqlite3_file.pMethods
element will be valid after xOpen returns regardless of the success
or failure of the xOpen call.
The flags argument to xAccess() may be SQLITE_ACCESS_EXISTS
to test for the existence of a file, or SQLITE_ACCESS_READWRITE
to
test whether a file is readable and writable, or SQLITE_ACCESS_READ
to test whether a file is at least readable. The file can be a
directory.
SQLite will always allocate at least mxPathname+1 bytes for the
output buffer xFullPathname. The exact size of the output buffer
is also passed as a parameter to both methods. If the output buffer
is not large enough, SQLITE_CANTOPEN
should be returned. Since this is
handled as a fatal error by SQLite, vfs implementations should endeavor
to prevent this by setting mxPathname to a sufficiently large value.
The xRandomness(), xSleep(), xCurrentTime(), and xCurrentTimeInt64()
interfaces are not strictly a part of the filesystem, but they are
included in the VFS structure for completeness.
The xRandomness() function attempts to return nBytes bytes
of good-quality randomness into zOut. The return value is
the actual number of bytes of randomness obtained.
The xSleep() method causes the calling thread to sleep for at
least the number of microseconds given. The xCurrentTime()
method returns a Julian Day Number for the current date and time as
a floating point value.
The xCurrentTimeInt64() method returns, as an integer, the Julian
Day Number multiplied by 86400000 (the number of milliseconds in
a 24-hour day).
SQLite will use the xCurrentTimeInt64() method to get the current
date and time if that method is available (if iVersion is 2 or
greater and the function pointer is not NULL) and will fall back
to xCurrentTime() if xCurrentTimeInt64() is unavailable.
The xSetSystemCall(), xGetSystemCall(), and xNestSystemCall() interfaces
are not used by the SQLite core. These optional interfaces are provided
by some VFSes to facilitate testing of the VFS code. By overriding
system calls with functions under its control, a test program can
simulate faults and error conditions that would otherwise be difficult
or impossible to induce. The set of system calls that can be overridden
varies from one VFS to another, and from one version of the same VFS to the
next. Applications that use these interfaces must be prepared for any
or all of these interfaces to be NULL or for their behavior to change
from one release to the next. Applications must not attempt to access
any of these methods if the iVersion of the VFS is less than 3.
Virtual Table Instance Object
struct sqlite3_vtab {
const sqlite3_module *pModule; /* The module for this virtual table */
int nRef; /* NO LONGER USED */
char *zErrMsg; /* Error message from sqlite3_mprintf() */
/* Virtual table implementations will typically add additional fields */
};
Every virtual table module
implementation uses a subclass
of this object to describe a particular instance
of the virtual table
. Each subclass will
be tailored to the specific needs of the module implementation.
The purpose of this superclass is to define certain fields that are
common to all module implementations.
Virtual tables methods can set an error message by assigning a
string obtained from sqlite3_mprintf()
to zErrMsg. The method should
take care that any prior string is freed by a call to sqlite3_free()
prior to assigning a new string to zErrMsg. After the error message
is delivered up to the client application, the string will be automatically
freed by sqlite3_free() and the zErrMsg field will be zeroed.
Obtain Aggregate Function Context
void *sqlite3_aggregate_context(sqlite3_context*, int nBytes);
Implementations of aggregate SQL functions use this
routine to allocate memory for storing their state.
The first time the sqlite3_aggregate_context(C,N) routine is called
for a particular aggregate function, SQLite
allocates N of memory, zeroes out that memory, and returns a pointer
to the new memory. On second and subsequent calls to
sqlite3_aggregate_context() for the same aggregate function instance,
the same buffer is returned. Sqlite3_aggregate_context() is normally
called once for each invocation of the xStep callback and then one
last time when the xFinal callback is invoked. When no rows match
an aggregate query, the xStep() callback of the aggregate function
implementation is never called and xFinal() is called exactly once.
In those cases, sqlite3_aggregate_context() might be called for the
first time from within xFinal().
The sqlite3_aggregate_context(C,N) routine returns a NULL pointer if N is
less than or equal to zero or if a memory allocate error occurs.
The amount of space allocated by sqlite3_aggregate_context(C,N) is
determined by the N parameter on first successful call. Changing the
value of N in subsequent call to sqlite3_aggregate_context() within
the same aggregate function instance will not resize the memory
allocation.
SQLite automatically frees the memory allocated by
sqlite3_aggregate_context() when the aggregate query concludes.
The first parameter must be a copy of the
SQL function context
that is the first parameter
to the xStep or xFinal callback routine that implements the aggregate
function.
This routine must be called from the same thread in which
the aggregate SQL function is running.
Automatically Load Statically Linked Extensions
int sqlite3_auto_extension(void (*xEntryPoint)(void));
This interface causes the xEntryPoint() function to be invoked for
each new database connection
that is created. The idea here is that
xEntryPoint() is the entry point for a statically linked SQLite extension
that is to be automatically loaded into all new database connections.
Even though the function prototype shows that xEntryPoint() takes
no arguments and returns void, SQLite invokes xEntryPoint() with three
arguments and expects and integer result as if the signature of the
entry point where as follows:
int xEntryPoint(
sqlite3 *db,
const char **pzErrMsg,
const struct sqlite3_api_routines *pThunk
);
If the xEntryPoint routine encounters an error, it should make *pzErrMsg
point to an appropriate error message (obtained from sqlite3_mprintf()
)
and return an appropriate error code
. SQLite ensures that *pzErrMsg
is NULL before calling the xEntryPoint(). SQLite will invoke
sqlite3_free()
on *pzErrMsg after xEntryPoint() returns. If any
xEntryPoint() returns an error, the sqlite3_open()
, sqlite3_open16()
,
or sqlite3_open_v2()
call that provoked the xEntryPoint() will fail.
Calling sqlite3_auto_extension(X) with an entry point X that is already
on the list of automatic extensions is a harmless no-op. No entry point
will be called more than once for each database connection that is opened.
See also: sqlite3_reset_auto_extension()
.
Number Of SQL Parameters
int sqlite3_bind_parameter_count(sqlite3_stmt*);
This routine can be used to find the number of SQL parameters
in a prepared statement
. SQL parameters are tokens of the
form "?", "?NNN", ":AAA", "$AAA", or "@AAA" that serve as
placeholders for values that are bound
to the parameters at a later time.
This routine actually returns the index of the largest (rightmost)
parameter. For all forms except ?NNN, this will correspond to the
number of unique parameters. If parameters of the ?NNN form are used,
there may be gaps in the list.
See also: sqlite3_bind()
,
sqlite3_bind_parameter_name()
, and
sqlite3_bind_parameter_index()
.
Index Of A Parameter With A Given Name
int sqlite3_bind_parameter_index(sqlite3_stmt*, const char *zName);
Return the index of an SQL parameter given its name. The
index value returned is suitable for use as the second
parameter to sqlite3_bind()
. A zero
is returned if no matching parameter is found. The parameter
name must be given in UTF-8 even if the original statement
was prepared from UTF-16 text using sqlite3_prepare16_v2()
.
See also: sqlite3_bind()
,
sqlite3_bind_parameter_count()
, and
sqlite3_bind_parameter_index()
.
Name Of A Host Parameter
const char *sqlite3_bind_parameter_name(sqlite3_stmt*, int);
The sqlite3_bind_parameter_name(P,N) interface returns
the name of the N-th SQL parameter
in the prepared statement
P.
SQL parameters of the form "?NNN" or ":AAA" or "@AAA" or "$AAA"
have a name which is the string "?NNN" or ":AAA" or "@AAA" or "$AAA"
respectively.
In other words, the initial ":" or "$" or "@" or "?"
is included as part of the name.
Parameters of the form "?" without a following integer have no name
and are referred to as "nameless" or "anonymous parameters".
The first host parameter has an index of 1, not 0.
If the value N is out of range or if the N-th parameter is
nameless, then NULL is returned. The returned string is
always in UTF-8 encoding even if the named parameter was
originally specified as UTF-16 in sqlite3_prepare16()
or
sqlite3_prepare16_v2()
.
See also: sqlite3_bind()
,
sqlite3_bind_parameter_count()
, and
sqlite3_bind_parameter_index()
.
Return The Size Of An Open BLOB
int sqlite3_blob_bytes(sqlite3_blob *);
Returns the size in bytes of the BLOB accessible via the
successfully opened BLOB handle
in its only argument. The
incremental blob I/O routines can only read or overwriting existing
blob content; they cannot change the size of a blob.
This routine only works on a BLOB handle
which has been created
by a prior successful call to sqlite3_blob_open()
and which has not
been closed by sqlite3_blob_close()
. Passing any other pointer in
to this routine results in undefined and probably undesirable behavior.
Close A BLOB Handle
int sqlite3_blob_close(sqlite3_blob *);
Closes an open BLOB handle
.
Closing a BLOB shall cause the current transaction to commit
if there are no other BLOBs, no pending prepared statements, and the
database connection is in autocommit mode
.
If any writes were made to the BLOB, they might be held in cache
until the close operation if they will fit.
Closing the BLOB often forces the changes
out to disk and so if any I/O errors occur, they will likely occur
at the time when the BLOB is closed. Any errors that occur during
closing are reported as a non-zero return value.
The BLOB is closed unconditionally. Even if this routine returns
an error code, the BLOB is still closed.
Calling this routine with a null pointer (such as would be returned
by a failed call to sqlite3_blob_open()
) is a harmless no-op.
Open A BLOB For Incremental I/O
int sqlite3_blob_open(
sqlite3*,
const char *zDb,
const char *zTable,
const char *zColumn,
sqlite3_int64 iRow,
int flags,
sqlite3_blob **ppBlob
);
This interfaces opens a handle
to the BLOB located
in row iRow, column zColumn, table zTable in database zDb;
in other words, the same BLOB that would be selected by:
SELECT zColumn FROM zDb.zTable WHERE rowid
= iRow;
If the flags parameter is non-zero, then the BLOB is opened for read
and write access. If it is zero, the BLOB is opened for read access.
It is not possible to open a column that is part of an index or primary
key for writing. If foreign key constraints
are enabled, it is
not possible to open a column that is part of a child key
for writing.
Note that the database name is not the filename that contains
the database but rather the symbolic name of the database that
appears after the AS keyword when the database is connected using ATTACH
.
For the main database file, the database name is "main".
For TEMP tables, the database name is "temp".
On success, SQLITE_OK
is returned and the new BLOB handle
is written
to *ppBlob. Otherwise an error code
is returned and *ppBlob is set
to be a null pointer.
This function sets the database connection
error code and message
accessible via sqlite3_errcode()
and sqlite3_errmsg()
and related
functions. Note that the *ppBlob variable is always initialized in a
way that makes it safe to invoke sqlite3_blob_close()
on *ppBlob
regardless of the success or failure of this routine.
If the row that a BLOB handle points to is modified by an
UPDATE
, DELETE
, or by ON CONFLICT
side-effects
then the BLOB handle is marked as "expired".
This is true if any column of the row is changed, even a column
other than the one the BLOB handle is open on.
Calls to sqlite3_blob_read()
and sqlite3_blob_write()
for
an expired BLOB handle fail with a return code of SQLITE_ABORT
.
Changes written into a BLOB prior to the BLOB expiring are not
rolled back by the expiration of the BLOB. Such changes will eventually
commit if the transaction continues to completion.
Use the sqlite3_blob_bytes()
interface to determine the size of
the opened blob. The size of a blob may not be changed by this
interface. Use the UPDATE
SQL command to change the size of a
blob.
The sqlite3_bind_zeroblob()
and sqlite3_result_zeroblob()
interfaces
and the built-in zeroblob
SQL function can be used, if desired,
to create an empty, zero-filled blob in which to read or write using
this interface.
To avoid a resource leak, every open BLOB handle
should eventually
be released by a call to sqlite3_blob_close()
.
Read Data From A BLOB Incrementally
int sqlite3_blob_read(sqlite3_blob *, void *Z, int N, int iOffset);
This function is used to read data from an open BLOB handle
into a
caller-supplied buffer. N bytes of data are copied into buffer Z
from the open BLOB, starting at offset iOffset.
If offset iOffset is less than N bytes from the end of the BLOB,
SQLITE_ERROR
is returned and no data is read. If N or iOffset is
less than zero, SQLITE_ERROR
is returned and no data is read.
The size of the blob (and hence the maximum value of N+iOffset)
can be determined using the sqlite3_blob_bytes()
interface.
An attempt to read from an expired BLOB handle
fails with an
error code of SQLITE_ABORT
.
On success, sqlite3_blob_read() returns SQLITE_OK.
Otherwise, an error code
or an extended error code
is returned.
This routine only works on a BLOB handle
which has been created
by a prior successful call to sqlite3_blob_open()
and which has not
been closed by sqlite3_blob_close()
. Passing any other pointer in
to this routine results in undefined and probably undesirable behavior.
See also: sqlite3_blob_write()
.
Move a BLOB Handle to a New Row
int sqlite3_blob_reopen(sqlite3_blob *, sqlite3_int64);
This function is used to move an existing blob handle so that it points
to a different row of the same database table. The new row is identified
by the rowid value passed as the second argument. Only the row can be
changed. The database, table and column on which the blob handle is open
remain the same. Moving an existing blob handle to a new row can be
faster than closing the existing handle and opening a new one.
The new row must meet the same criteria as for sqlite3_blob_open()
-
it must exist and there must be either a blob or text value stored in
the nominated column. If the new row is not present in the table, or if
it does not contain a blob or text value, or if another error occurs, an
SQLite error code is returned and the blob handle is considered aborted.
All subsequent calls to sqlite3_blob_read()
, sqlite3_blob_write()
or
sqlite3_blob_reopen()
on an aborted blob handle immediately return
SQLITE_ABORT. Calling sqlite3_blob_bytes()
on an aborted blob handle
always returns zero.
This function sets the database handle error code and message.
Write Data Into A BLOB Incrementally
int sqlite3_blob_write(sqlite3_blob *, const void *z, int n, int iOffset);
This function is used to write data into an open BLOB handle
from a
caller-supplied buffer. N bytes of data are copied from the buffer Z
into the open BLOB, starting at offset iOffset.
If the BLOB handle
passed as the first argument was not opened for
writing (the flags parameter to sqlite3_blob_open()
was zero),
this function returns SQLITE_READONLY
.
This function may only modify the contents of the BLOB; it is
not possible to increase the size of a BLOB using this API.
If offset iOffset is less than N bytes from the end of the BLOB,
SQLITE_ERROR
is returned and no data is written. If N is
less than zero SQLITE_ERROR
is returned and no data is written.
The size of the BLOB (and hence the maximum value of N+iOffset)
can be determined using the sqlite3_blob_bytes()
interface.
An attempt to write to an expired BLOB handle
fails with an
error code of SQLITE_ABORT
. Writes to the BLOB that occurred
before the BLOB handle
expired are not rolled back by the
expiration of the handle, though of course those changes might
have been overwritten by the statement that expired the BLOB handle
or by other independent statements.
On success, sqlite3_blob_write() returns SQLITE_OK.
Otherwise, an error code
or an extended error code
is returned.
This routine only works on a BLOB handle
which has been created
by a prior successful call to sqlite3_blob_open()
and which has not
been closed by sqlite3_blob_close()
. Passing any other pointer in
to this routine results in undefined and probably undesirable behavior.
See also: sqlite3_blob_read()
.
Register A Callback To Handle SQLITE_BUSY Errors
int sqlite3_busy_handler(sqlite3*, int(*)(void*,int), void*);
This routine sets a callback function that might be invoked whenever
an attempt is made to open a database table that another thread
or process has locked.
If the busy callback is NULL, then SQLITE_BUSY
or SQLITE_IOERR_BLOCKED
is returned immediately upon encountering the lock. If the busy callback
is not NULL, then the callback might be invoked with two arguments.
The first argument to the busy handler is a copy of the void* pointer which
is the third argument to sqlite3_busy_handler(). The second argument to
the busy handler callback is the number of times that the busy handler has
been invoked for this locking event. If the
busy callback returns 0, then no additional attempts are made to
access the database and SQLITE_BUSY
or SQLITE_IOERR_BLOCKED
is returned.
If the callback returns non-zero, then another attempt
is made to open the database for reading and the cycle repeats.
The presence of a busy handler does not guarantee that it will be invoked
when there is lock contention. If SQLite determines that invoking the busy
handler could result in a deadlock, it will go ahead and return SQLITE_BUSY
or SQLITE_IOERR_BLOCKED
instead of invoking the busy handler.
Consider a scenario where one process is holding a read lock that
it is trying to promote to a reserved lock and
a second process is holding a reserved lock that it is trying
to promote to an exclusive lock. The first process cannot proceed
because it is blocked by the second and the second process cannot
proceed because it is blocked by the first. If both processes
invoke the busy handlers, neither will make any progress. Therefore,
SQLite returns SQLITE_BUSY
for the first process, hoping that this
will induce the first process to release its read lock and allow
the second process to proceed.
The default busy callback is NULL.
The SQLITE_BUSY
error is converted to SQLITE_IOERR_BLOCKED
when SQLite is in the middle of a large transaction where all the
changes will not fit into the in-memory cache. SQLite will
already hold a RESERVED lock on the database file, but it needs
to promote this lock to EXCLUSIVE so that it can spill cache
pages into the database file without harm to concurrent
readers. If it is unable to promote the lock, then the in-memory
cache will be left in an inconsistent state and so the error
code is promoted from the relatively benign SQLITE_BUSY
to
the more severe SQLITE_IOERR_BLOCKED
. This error code promotion
forces an automatic rollback of the changes. See the
CorruptionFollowingBusyError
wiki page for a discussion of why
this is important.
There can only be a single busy handler defined for each
database connection
. Setting a new busy handler clears any
previously set handler. Note that calling sqlite3_busy_timeout()
will also set or clear the busy handler.
The busy callback should not take any actions which modify the
database connection that invoked the busy handler. Any such actions
result in undefined behavior.
A busy handler must not close the database connection
or prepared statement
that invoked the busy handler.
Set A Busy Timeout
int sqlite3_busy_timeout(sqlite3*, int ms);
This routine sets a busy handler
that sleeps
for a specified amount of time when a table is locked. The handler
will sleep multiple times until at least "ms" milliseconds of sleeping
have accumulated. After at least "ms" milliseconds of sleeping,
the handler returns 0 which causes sqlite3_step()
to return
SQLITE_BUSY
or SQLITE_IOERR_BLOCKED
.
Calling this routine with an argument less than or equal to zero
turns off all busy handlers.
There can only be a single busy handler for a particular
database connection
any any given moment. If another busy handler
was defined (using sqlite3_busy_handler()
) prior to calling
this routine, that other busy handler is cleared.
Count The Number Of Rows Modified
int sqlite3_changes(sqlite3*);
This function returns the number of database rows that were changed
or inserted or deleted by the most recently completed SQL statement
on the database connection
specified by the first parameter.
Only changes that are directly specified by the INSERT
, UPDATE
,
or DELETE
statement are counted. Auxiliary changes caused by
triggers or foreign key actions
are not counted. Use the
sqlite3_total_changes()
function to find the total number of changes
including changes caused by triggers and foreign key actions.
Changes to a view that are simulated by an INSTEAD OF trigger
are not counted. Only real table changes are counted.
A "row change" is a change to a single row of a single table
caused by an INSERT, DELETE, or UPDATE statement. Rows that
are changed as side effects of REPLACE
constraint resolution,
rollback, ABORT processing, DROP TABLE
, or by any other
mechanisms do not count as direct row changes.
A "trigger context" is a scope of execution that begins and
ends with the script of a trigger
.
Most SQL statements are
evaluated outside of any trigger. This is the "top level"
trigger context. If a trigger fires from the top level, a
new trigger context is entered for the duration of that one
trigger. Subtriggers create subcontexts for their duration.
Calling sqlite3_exec()
or sqlite3_step()
recursively does
not create a new trigger context.
This function returns the number of direct row changes in the
most recent INSERT, UPDATE, or DELETE statement within the same
trigger context.
Thus, when called from the top level, this function returns the
number of changes in the most recent INSERT, UPDATE, or DELETE
that also occurred at the top level. Within the body of a trigger,
the sqlite3_changes() interface can be called to find the number of
changes in the most recently completed INSERT, UPDATE, or DELETE
statement within the body of the same trigger.
However, the number returned does not include changes
caused by subtriggers since those have their own context.
See also the sqlite3_total_changes()
interface, the
count_changes pragma
, and the changes() SQL function
.
If a separate thread makes changes on the same database connection
while sqlite3_changes()
is running then the value returned
is unpredictable and not meaningful.
Reset All Bindings On A Prepared Statement
int sqlite3_clear_bindings(sqlite3_stmt*);
Contrary to the intuition of many, sqlite3_reset()
does not reset
the bindings
on a prepared statement
.
Use this routine to reset all host parameters to NULL.
Closing A Database Connection
int sqlite3_close(sqlite3 *);
The sqlite3_close() routine is the destructor for the sqlite3
object.
Calls to sqlite3_close() return SQLITE_OK if the sqlite3
object is
successfully destroyed and all associated resources are deallocated.
Applications must finalize
all prepared statements
and close
all BLOB handles
associated with
the sqlite3
object prior to attempting to close the object. If
sqlite3_close() is called on a database connection
that still has
outstanding prepared statements
or BLOB handles
, then it returns
SQLITE_BUSY.
If sqlite3_close()
is invoked while a transaction is open,
the transaction is automatically rolled back.
The C parameter to sqlite3_close(C)
must be either a NULL
pointer or an sqlite3
object pointer obtained
from sqlite3_open()
, sqlite3_open16()
, or
sqlite3_open_v2()
, and not previously closed.
Calling sqlite3_close() with a NULL pointer argument is a
harmless no-op.
Number Of Columns In A Result Set
int sqlite3_column_count(sqlite3_stmt *pStmt);
Return the number of columns in the result set returned by the
prepared statement
. This routine returns 0 if pStmt is an SQL
statement that does not return data (for example an UPDATE
).
See also: sqlite3_data_count()
Configuring The SQLite Library
int sqlite3_config(int, ...);
The sqlite3_config() interface is used to make global configuration
changes to SQLite in order to tune SQLite to the specific needs of
the application. The default configuration is recommended for most
applications and so this routine is usually not necessary. It is
provided to support rare applications with unusual needs.
The sqlite3_config() interface is not threadsafe. The application
must insure that no other SQLite interfaces are invoked by other
threads while sqlite3_config() is running. Furthermore, sqlite3_config()
may only be invoked prior to library initialization using
sqlite3_initialize()
or after shutdown by sqlite3_shutdown()
.
If sqlite3_config() is called after sqlite3_initialize()
and before
sqlite3_shutdown()
then it will return SQLITE_MISUSE.
Note, however, that sqlite3_config() can be called as part of the
implementation of an application-defined sqlite3_os_init()
.
The first argument to sqlite3_config() is an integer
configuration option
that determines
what property of SQLite is to be configured. Subsequent arguments
vary depending on the configuration option
in the first argument.
When a configuration option is set, sqlite3_config() returns SQLITE_OK
.
If the option is unknown or SQLite is unable to set the option
then this routine returns a non-zero error code
.
Database Connection For Functions
sqlite3 *sqlite3_context_db_handle(sqlite3_context*);
The sqlite3_context_db_handle() interface returns a copy of
the pointer to the database connection
(the 1st parameter)
of the sqlite3_create_function()
and sqlite3_create_function16()
routines that originally
registered the application defined function.
Number of columns in a result set
int sqlite3_data_count(sqlite3_stmt *pStmt);
The sqlite3_data_count(P) interface returns the number of columns in the
current row of the result set of prepared statement
P.
If prepared statement P does not have results ready to return
(via calls to the sqlite3_column_*()
of
interfaces) then sqlite3_data_count(P) returns 0.
The sqlite3_data_count(P) routine also returns 0 if P is a NULL pointer.
The sqlite3_data_count(P) routine returns 0 if the previous call to
sqlite3_step
(P) returned SQLITE_DONE
. The sqlite3_data_count(P)
will return non-zero if previous call to sqlite3_step
(P) returned
SQLITE_ROW
, except in the case of the PRAGMA incremental_vacuum
where it always returns zero since each step of that multi-step
pragma returns 0 columns of data.
See also: sqlite3_column_count()
Configure database connections
int sqlite3_db_config(sqlite3*, int op, ...);
The sqlite3_db_config() interface is used to make configuration
changes to a database connection
. The interface is similar to
sqlite3_config()
except that the changes apply to a single
database connection
(specified in the first argument).
The second argument to sqlite3_db_config(D,V,...) is the
configuration verb
- an integer code
that indicates what aspect of the database connection
is being configured.
Subsequent arguments vary depending on the configuration verb.
Calls to sqlite3_db_config() return SQLITE_OK if and only if
the call is considered successful.
Return The Filename For A Database Connection
const char *sqlite3_db_filename(sqlite3 *db, const char *zDbName);
The sqlite3_db_filename(D,N) interface returns a pointer to a filename
associated with database N of connection D. The main database file
has the name "main". If there is no attached database N on the database
connection D, or if database N is a temporary or in-memory database, then
a NULL pointer is returned.
The filename returned by this function is the output of the
xFullPathname method of the VFS
. In other words, the filename
will be an absolute pathname, even if the filename used
to open the database originally was a URI or relative pathname.
Find The Database Handle Of A Prepared Statement
sqlite3 *sqlite3_db_handle(sqlite3_stmt*);
The sqlite3_db_handle interface returns the database connection
handle
to which a prepared statement
belongs. The database connection
returned by sqlite3_db_handle is the same database connection
that was the first argument
to the sqlite3_prepare_v2()
call (or its variants) that was used to
create the statement in the first place.
Retrieve the mutex for a database connection
sqlite3_mutex *sqlite3_db_mutex(sqlite3*);
This interface returns a pointer the sqlite3_mutex
object that
serializes access to the database connection
given in the argument
when the threading mode
is Serialized.
If the threading mode
is Single-thread or Multi-thread then this
routine returns a NULL pointer.
Free Memory Used By A Database Connection
int sqlite3_db_release_memory(sqlite3*);
The sqlite3_db_release_memory(D) interface attempts to free as much heap
memory as possible from database connection D. Unlike the
sqlite3_release_memory()
interface, this interface is effect even
when then SQLITE_ENABLE_MEMORY_MANAGEMENT
compile-time option is
omitted.
See also: sqlite3_release_memory()
Database Connection Status
int sqlite3_db_status(sqlite3*, int op, int *pCur, int *pHiwtr, int resetFlg);
This interface is used to retrieve runtime status information
about a single database connection
. The first argument is the
database connection object to be interrogated. The second argument
is an integer constant, taken from the set of
SQLITE_DBSTATUS options
, that
determines the parameter to interrogate. The set of
SQLITE_DBSTATUS options
is likely
to grow in future releases of SQLite.
The current value of the requested parameter is written into *pCur
and the highest instantaneous value is written into *pHiwtr. If
the resetFlg is true, then the highest instantaneous value is
reset back down to the current value.
The sqlite3_db_status() routine returns SQLITE_OK on success and a
non-zero error code
on failure.
See also: sqlite3_status()
and sqlite3_stmt_status()
.
Declare The Schema Of A Virtual Table
int sqlite3_declare_vtab(sqlite3*, const char *zSQL);
The xCreate
and xConnect
methods of a
virtual table module
call this interface
to declare the format (the names and datatypes of the columns) of
the virtual tables they implement.
Enable Or Disable Extension Loading
int sqlite3_enable_load_extension(sqlite3 *db, int onoff);
So as not to open security holes in older applications that are
unprepared to deal with extension loading, and as a means of disabling
extension loading while evaluating user-entered SQL, the following API
is provided to turn the sqlite3_load_extension()
mechanism on and off.
Extension loading is off by default. See ticket #1863.
Call the sqlite3_enable_load_extension() routine with onoff==1
to turn extension loading on and call it with onoff==0 to turn
it back off again.
One-Step Query Execution Interface
int sqlite3_exec(
sqlite3*, /* An open database */
const char *sql, /* SQL to be evaluated */
int (*callback)(void*,int,char**,char**), /* Callback function */
void *, /* 1st argument to callback */
char **errmsg /* Error msg written here */
);
The sqlite3_exec() interface is a convenience wrapper around
sqlite3_prepare_v2()
, sqlite3_step()
, and sqlite3_finalize()
,
that allows an application to run multiple statements of SQL
without having to use a lot of C code.
The sqlite3_exec() interface runs zero or more UTF-8 encoded,
semicolon-separate SQL statements passed into its 2nd argument,
in the context of the database connection
passed in as its 1st
argument. If the callback function of the 3rd argument to
sqlite3_exec() is not NULL, then it is invoked for each result row
coming out of the evaluated SQL statements. The 4th argument to
sqlite3_exec() is relayed through to the 1st argument of each
callback invocation. If the callback pointer to sqlite3_exec()
is NULL, then no callback is ever invoked and result rows are
ignored.
If an error occurs while evaluating the SQL statements passed into
sqlite3_exec(), then execution of the current statement stops and
subsequent statements are skipped. If the 5th parameter to sqlite3_exec()
is not NULL then any error message is written into memory obtained
from sqlite3_malloc()
and passed back through the 5th parameter.
To avoid memory leaks, the application should invoke sqlite3_free()
on error message strings returned through the 5th parameter of
of sqlite3_exec() after the error message string is no longer needed.
If the 5th parameter to sqlite3_exec() is not NULL and no errors
occur, then sqlite3_exec() sets the pointer in its 5th parameter to
NULL before returning.
If an sqlite3_exec() callback returns non-zero, the sqlite3_exec()
routine returns SQLITE_ABORT without invoking the callback again and
without running any subsequent SQL statements.
The 2nd argument to the sqlite3_exec() callback function is the
number of columns in the result. The 3rd argument to the sqlite3_exec()
callback is an array of pointers to strings obtained as if from
sqlite3_column_text()
, one for each column. If an element of a
result row is NULL then the corresponding string pointer for the
sqlite3_exec() callback is a NULL pointer. The 4th argument to the
sqlite3_exec() callback is an array of pointers to strings where each
entry represents the name of corresponding result column as obtained
from sqlite3_column_name()
.
If the 2nd parameter to sqlite3_exec() is a NULL pointer, a pointer
to an empty string, or a pointer that contains only whitespace and/or
SQL comments, then no SQL statements are evaluated and the database
is not changed.
Restrictions:
- The application must insure that the 1st parameter to sqlite3_exec()
is a valid and open database connection
.
- The application must not close database connection
specified by
the 1st parameter to sqlite3_exec() while sqlite3_exec() is running.
- The application must not modify the SQL statement text passed into
the 2nd parameter of sqlite3_exec() while sqlite3_exec() is running.
Enable Or Disable Extended Result Codes
int sqlite3_extended_result_codes(sqlite3*, int onoff);
The sqlite3_extended_result_codes() routine enables or disables the
extended result codes
feature of SQLite. The extended result
codes are disabled by default for historical compatibility.
Low-Level Control Of Database Files
int sqlite3_file_control(sqlite3*, const char *zDbName, int op, void*);
The sqlite3_file_control()
interface makes a direct call to the
xFileControl method for the sqlite3_io_methods
object associated
with a particular database identified by the second argument. The
name of the database is "main" for the main database or "temp" for the
TEMP database, or the name that appears after the AS keyword for
databases that are added using the ATTACH
SQL command.
A NULL pointer can be used in place of "main" to refer to the
main database file.
The third and fourth parameters to this routine
are passed directly through to the second and third parameters of
the xFileControl method. The return value of the xFileControl
method becomes the return value of this routine.
The SQLITE_FCNTL_FILE_POINTER value for the op parameter causes
a pointer to the underlying sqlite3_file
object to be written into
the space pointed to by the 4th parameter. The SQLITE_FCNTL_FILE_POINTER
case is a short-circuit path which does not actually invoke the
underlying sqlite3_io_methods.xFileControl method.
If the second parameter (zDbName) does not match the name of any
open database file, then SQLITE_ERROR is returned. This error
code is not remembered and will not be recalled by sqlite3_errcode()
or sqlite3_errmsg()
. The underlying xFileControl method might
also return SQLITE_ERROR. There is no way to distinguish between
an incorrect zDbName and an SQLITE_ERROR return from the underlying
xFileControl method.
See also: SQLITE_FCNTL_LOCKSTATE
Destroy A Prepared Statement Object
int sqlite3_finalize(sqlite3_stmt *pStmt);
The sqlite3_finalize() function is called to delete a prepared statement
.
If the most recent evaluation of the statement encountered no errors
or if the statement is never been evaluated, then sqlite3_finalize() returns
SQLITE_OK. If the most recent evaluation of statement S failed, then
sqlite3_finalize(S) returns the appropriate error code
or
extended error code
.
The sqlite3_finalize(S) routine can be called at any point during
the life cycle of prepared statement
S:
before statement S is ever evaluated, after
one or more calls to sqlite3_reset()
, or after any call
to sqlite3_step()
regardless of whether or not the statement has
completed execution.
Invoking sqlite3_finalize() on a NULL pointer is a harmless no-op.
The application must finalize every prepared statement
in order to avoid
resource leaks. It is a grievous error for the application to try to use
a prepared statement after it has been finalized. Any use of a prepared
statement after it has been finalized can result in undefined and
undesirable behavior such as segfaults and heap corruption.
Interrupt A Long-Running Query
void sqlite3_interrupt(sqlite3*);
This function causes any pending database operation to abort and
return at its earliest opportunity. This routine is typically
called in response to a user action such as pressing "Cancel"
or Ctrl-C where the user wants a long query operation to halt
immediately.
It is safe to call this routine from a thread different from the
thread that is currently running the database operation. But it
is not safe to call this routine with a database connection
that
is closed or might close before sqlite3_interrupt() returns.
If an SQL operation is very nearly finished at the time when
sqlite3_interrupt() is called, then it might not have an opportunity
to be interrupted and might continue to completion.
An SQL operation that is interrupted will return SQLITE_INTERRUPT
.
If the interrupted SQL operation is an INSERT, UPDATE, or DELETE
that is inside an explicit transaction, then the entire transaction
will be rolled back automatically.
The sqlite3_interrupt(D) call is in effect until all currently running
SQL statements on database connection
D complete. Any new SQL statements
that are started after the sqlite3_interrupt() call and before the
running statements reaches zero are interrupted as if they had been
running prior to the sqlite3_interrupt() call. New SQL statements
that are started after the running statement count reaches zero are
not effected by the sqlite3_interrupt().
A call to sqlite3_interrupt(D) that occurs when there are no running
SQL statements is a no-op and has no effect on SQL statements
that are started after the sqlite3_interrupt() call returns.
If the database connection closes while sqlite3_interrupt()
is running then bad things will likely happen.
Last Insert Rowid
sqlite3_int64 sqlite3_last_insert_rowid(sqlite3*);
Each entry in an SQLite table has a unique 64-bit signed
integer key called the "rowid"
. The rowid is always available
as an undeclared column named ROWID, OID, or _ROWID_ as long as those
names are not also used by explicitly declared columns. If
the table has a column of type INTEGER PRIMARY KEY
then that column
is another alias for the rowid.
This routine returns the rowid
of the most recent
successful INSERT
into the database from the database connection
in the first argument. As of SQLite version 3.7.7, this routines
records the last insert rowid of both ordinary tables and virtual tables
.
If no successful INSERT
s
have ever occurred on that database connection, zero is returned.
If an INSERT
occurs within a trigger or within a virtual table
method, then this routine will return the rowid
of the inserted
row as long as the trigger or virtual table method is running.
But once the trigger or virtual table method ends, the value returned
by this routine reverts to what it was before the trigger or virtual
table method began.
An INSERT
that fails due to a constraint violation is not a
successful INSERT
and does not change the value returned by this
routine. Thus INSERT OR FAIL, INSERT OR IGNORE, INSERT OR ROLLBACK,
and INSERT OR ABORT make no changes to the return value of this
routine when their insertion fails. When INSERT OR REPLACE
encounters a constraint violation, it does not fail. The
INSERT continues to completion after deleting rows that caused
the constraint problem so INSERT OR REPLACE will always change
the return value of this interface.
For the purposes of this routine, an INSERT
is considered to
be successful even if it is subsequently rolled back.
This function is accessible to SQL statements via the
last_insert_rowid() SQL function
.
If a separate thread performs a new INSERT
on the same
database connection while the sqlite3_last_insert_rowid()
function is running and thus changes the last insert rowid
,
then the value returned by sqlite3_last_insert_rowid()
is
unpredictable and might not equal either the old or the new
last insert rowid
.
Run-time Limits
int sqlite3_limit(sqlite3*, int id, int newVal);
This interface allows the size of various constructs to be limited
on a connection by connection basis. The first parameter is the
database connection
whose limit is to be set or queried. The
second parameter is one of the limit categories
that define a
class of constructs to be size limited. The third parameter is the
new limit for that construct.
If the new limit is a negative number, the limit is unchanged.
For each limit category SQLITE_LIMIT_NAME
there is a
hard upper bound
set at compile-time by a C preprocessor macro called
SQLITE_MAX_NAME
.
(The "_LIMIT_" in the name is changed to "_MAX_".)
Attempts to increase a limit above its hard upper bound are
silently truncated to the hard upper bound.
Regardless of whether or not the limit was changed, the
sqlite3_limit()
interface returns the prior value of the limit.
Hence, to find the current value of a limit without changing it,
simply invoke this interface with the third parameter set to -1.
Run-time limits are intended for use in applications that manage
both their own internal database and also databases that are controlled
by untrusted external sources. An example application might be a
web browser that has its own databases for storing history and
separate databases controlled by JavaScript applications downloaded
off the Internet. The internal databases can be given the
large, default limits. Databases managed by external sources can
be given much smaller limits designed to prevent a denial of service
attack. Developers might also want to use the sqlite3_set_authorizer()
interface to further control untrusted SQL. The size of the database
created by an untrusted script can be contained using the
max_page_count
PRAGMA
.
New run-time limit categories may be added in future releases.
Load An Extension
int sqlite3_load_extension(
sqlite3 *db, /* Load the extension into this database connection */
const char *zFile, /* Name of the shared library containing extension */
const char *zProc, /* Entry point. Derived from zFile if 0 */
char **pzErrMsg /* Put error message here if not 0 */
);
This interface loads an SQLite extension library from the named file.
The sqlite3_load_extension() interface attempts to load an
SQLite extension library contained in the file zFile.
The entry point is zProc.
zProc may be 0, in which case the name of the entry point
defaults to "sqlite3_extension_init".
The sqlite3_load_extension() interface returns
SQLITE_OK
on success and SQLITE_ERROR
if something goes wrong.
If an error occurs and pzErrMsg is not 0, then the
sqlite3_load_extension()
interface shall attempt to
fill *pzErrMsg with error message text stored in memory
obtained from sqlite3_malloc()
. The calling function
should free this memory by calling sqlite3_free()
.
Extension loading must be enabled using
sqlite3_enable_load_extension()
prior to calling this API,
otherwise an error will be returned.
See also the load_extension() SQL function
.
Error Logging Interface
void sqlite3_log(int iErrCode, const char *zFormat, ...);
The sqlite3_log()
interface writes a message into the error log
established by the SQLITE_CONFIG_LOG
option to sqlite3_config()
.
If logging is enabled, the zFormat string and subsequent arguments are
used with sqlite3_snprintf()
to generate the final output string.
The sqlite3_log() interface is intended for use by extensions such as
virtual tables, collating functions, and SQL functions. While there is
nothing to prevent an application from calling sqlite3_log(), doing so
is considered bad form.
The zFormat string must not be NULL.
To avoid deadlocks and other threading problems, the sqlite3_log() routine
will not use dynamically allocated memory. The log message is stored in
a fixed-length buffer on the stack. If the log message is longer than
a few hundred characters, it will be truncated to the length of the
buffer.
Find the next prepared statement
sqlite3_stmt *sqlite3_next_stmt(sqlite3 *pDb, sqlite3_stmt *pStmt);
This interface returns a pointer to the next prepared statement
after
pStmt associated with the database connection
pDb. If pStmt is NULL
then this interface returns a pointer to the first prepared statement
associated with the database connection pDb. If no prepared statement
satisfies the conditions of this routine, it returns NULL.
The database connection
pointer D in a call to
sqlite3_next_stmt(D,S)
must refer to an open database
connection and in particular must not be a NULL pointer.
Overload A Function For A Virtual Table
int sqlite3_overload_function(sqlite3*, const char *zFuncName, int nArg);
Virtual tables can provide alternative implementations of functions
using the xFindFunction
method of the virtual table module
.
But global versions of those functions
must exist in order to be overloaded.
This API makes sure a global version of a function with a particular
name and number of parameters exists. If no such function exists
before this API is called, a new function is created. The implementation
of the new function always causes an exception to be thrown. So
the new function is not good for anything by itself. Its only
purpose is to be a placeholder function that can be overloaded
by a virtual table
.
Query Progress Callbacks
void sqlite3_progress_handler(sqlite3*, int, int(*)(void*), void*);
The sqlite3_progress_handler(D,N,X,P) interface causes the callback
function X to be invoked periodically during long running calls to
sqlite3_exec()
, sqlite3_step()
and sqlite3_get_table()
for
database connection D. An example use for this
interface is to keep a GUI updated during a large query.
The parameter P is passed through as the only parameter to the
callback function X. The parameter N is the number of
virtual machine instructions
that are evaluated between successive
invocations of the callback X.
Only a single progress handler may be defined at one time per
database connection
; setting a new progress handler cancels the
old one. Setting parameter X to NULL disables the progress handler.
The progress handler is also disabled by setting N to a value less
than 1.
If the progress callback returns non-zero, the operation is
interrupted. This feature can be used to implement a
"Cancel" button on a GUI progress dialog box.
The progress handler callback must not do anything that will modify
the database connection that invoked the progress handler.
Note that sqlite3_prepare_v2()
and sqlite3_step()
both modify their
database connections for the meaning of "modify" in this paragraph.
Pseudo-Random Number Generator
void sqlite3_randomness(int N, void *P);
SQLite contains a high-quality pseudo-random number generator (PRNG) used to
select random ROWIDs
when inserting new records into a table that
already uses the largest possible ROWID
. The PRNG is also used for
the build-in random() and randomblob() SQL functions. This interface allows
applications to access the same PRNG for other purposes.
A call to this routine stores N bytes of randomness into buffer P.
The first time this routine is invoked (either internally or by
the application) the PRNG is seeded using randomness obtained
from the xRandomness method of the default sqlite3_vfs
object.
On all subsequent invocations, the pseudo-randomness is generated
internally and without recourse to the sqlite3_vfs
xRandomness
method.
Attempt To Free Heap Memory
int sqlite3_release_memory(int);
The sqlite3_release_memory() interface attempts to free N bytes
of heap memory by deallocating non-essential memory allocations
held by the database library. Memory used to cache database
pages to improve performance is an example of non-essential memory.
sqlite3_release_memory() returns the number of bytes actually freed,
which might be more or less than the amount requested.
The sqlite3_release_memory() routine is a no-op returning zero
if SQLite is not compiled with SQLITE_ENABLE_MEMORY_MANAGEMENT
.
See also: sqlite3_db_release_memory()
Reset A Prepared Statement Object
int sqlite3_reset(sqlite3_stmt *pStmt);
The sqlite3_reset() function is called to reset a prepared statement
object back to its initial state, ready to be re-executed.
Any SQL statement variables that had values bound to them using
the sqlite3_bind_*() API
retain their values.
Use sqlite3_clear_bindings()
to reset the bindings.
The sqlite3_reset(S)
interface resets the prepared statement
S
back to the beginning of its program.
If the most recent call to sqlite3_step(S)
for the
prepared statement
S returned SQLITE_ROW
or SQLITE_DONE
,
or if sqlite3_step(S)
has never before been called on S,
then sqlite3_reset(S)
returns SQLITE_OK
.
If the most recent call to sqlite3_step(S)
for the
prepared statement
S indicated an error, then
sqlite3_reset(S)
returns an appropriate error code
.
The sqlite3_reset(S)
interface does not change the values
of any bindings
on the prepared statement
S.
Reset Automatic Extension Loading
void sqlite3_reset_auto_extension(void);
This interface disables all automatic extensions previously
registered using sqlite3_auto_extension()
.
Compile-Time Authorization Callbacks
int sqlite3_set_authorizer(
sqlite3*,
int (*xAuth)(void*,int,const char*,const char*,const char*,const char*),
void *pUserData
);
This routine registers an authorizer callback with a particular
database connection
, supplied in the first argument.
The authorizer callback is invoked as SQL statements are being compiled
by sqlite3_prepare()
or its variants sqlite3_prepare_v2()
,
sqlite3_prepare16()
and sqlite3_prepare16_v2()
. At various
points during the compilation process, as logic is being created
to perform various actions, the authorizer callback is invoked to
see if those actions are allowed. The authorizer callback should
return SQLITE_OK
to allow the action, SQLITE_IGNORE
to disallow the
specific action but allow the SQL statement to continue to be
compiled, or SQLITE_DENY
to cause the entire SQL statement to be
rejected with an error. If the authorizer callback returns
any value other than SQLITE_IGNORE
, SQLITE_OK
, or SQLITE_DENY
then the sqlite3_prepare_v2()
or equivalent call that triggered
the authorizer will fail with an error message.
When the callback returns SQLITE_OK
, that means the operation
requested is ok. When the callback returns SQLITE_DENY
, the
sqlite3_prepare_v2()
or equivalent call that triggered the
authorizer will fail with an error message explaining that
access is denied.
The first parameter to the authorizer callback is a copy of the third
parameter to the sqlite3_set_authorizer() interface. The second parameter
to the callback is an integer action code
that specifies
the particular action to be authorized. The third through sixth parameters
to the callback are zero-terminated strings that contain additional
details about the action to be authorized.
If the action code is SQLITE_READ
and the callback returns SQLITE_IGNORE
then the
prepared statement
statement is constructed to substitute
a NULL value in place of the table column that would have
been read if SQLITE_OK
had been returned. The SQLITE_IGNORE
return can be used to deny an untrusted user access to individual
columns of a table.
If the action code is SQLITE_DELETE
and the callback returns
SQLITE_IGNORE
then the DELETE
operation proceeds but the
truncate optimization
is disabled and all rows are deleted individually.
An authorizer is used when preparing
SQL statements from an untrusted source, to ensure that the SQL statements
do not try to access data they are not allowed to see, or that they do not
try to execute malicious statements that damage the database. For
example, an application may allow a user to enter arbitrary
SQL queries for evaluation by a database. But the application does
not want the user to be able to make arbitrary changes to the
database. An authorizer could then be put in place while the
user-entered SQL is being prepared
that
disallows everything except SELECT
statements.
Applications that need to process SQL from untrusted sources
might also consider lowering resource limits using sqlite3_limit()
and limiting database size using the max_page_count
PRAGMA
in addition to using an authorizer.
Only a single authorizer can be in place on a database connection
at a time. Each call to sqlite3_set_authorizer overrides the
previous call. Disable the authorizer by installing a NULL callback.
The authorizer is disabled by default.
The authorizer callback must not do anything that will modify
the database connection that invoked the authorizer callback.
Note that sqlite3_prepare_v2()
and sqlite3_step()
both modify their
database connections for the meaning of "modify" in this paragraph.
When sqlite3_prepare_v2()
is used to prepare a statement, the
statement might be re-prepared during sqlite3_step()
due to a
schema change. Hence, the application should ensure that the
correct authorizer callback remains in place during the sqlite3_step()
.
Note that the authorizer callback is invoked only during
sqlite3_prepare()
or its variants. Authorization is not
performed during statement evaluation in sqlite3_step()
, unless
as stated in the previous paragraph, sqlite3_step() invokes
sqlite3_prepare_v2() to reprepare a statement after a schema change.
Suspend Execution For A Short Time
int sqlite3_sleep(int);
The sqlite3_sleep() function causes the current thread to suspend execution
for at least a number of milliseconds specified in its parameter.
If the operating system does not support sleep requests with
millisecond time resolution, then the time will be rounded up to
the nearest second. The number of milliseconds of sleep actually
requested from the operating system is returned.
SQLite implements this interface by calling the xSleep()
method of the default sqlite3_vfs
object. If the xSleep() method
of the default VFS is not implemented correctly, or not implemented at
all, then the behavior of sqlite3_sleep() may deviate from the description
in the previous paragraphs.
Deprecated Soft Heap Limit Interface
void sqlite3_soft_heap_limit(int N);
This is a deprecated version of the sqlite3_soft_heap_limit64()
interface. This routine is provided for historical compatibility
only. All new applications should use the
sqlite3_soft_heap_limit64()
interface rather than this one.
Impose A Limit On Heap Size
sqlite3_int64 sqlite3_soft_heap_limit64(sqlite3_int64 N);
The sqlite3_soft_heap_limit64() interface sets and/or queries the
soft limit on the amount of heap memory that may be allocated by SQLite.
SQLite strives to keep heap memory utilization below the soft heap
limit by reducing the number of pages held in the page cache
as heap memory usages approaches the limit.
The soft heap limit is "soft" because even though SQLite strives to stay
below the limit, it will exceed the limit rather than generate
an SQLITE_NOMEM
error. In other words, the soft heap limit
is advisory only.
The return value from sqlite3_soft_heap_limit64() is the size of
the soft heap limit prior to the call, or negative in the case of an
error. If the argument N is negative
then no change is made to the soft heap limit. Hence, the current
size of the soft heap limit can be determined by invoking
sqlite3_soft_heap_limit64() with a negative argument.
If the argument N is zero then the soft heap limit is disabled.
The soft heap limit is not enforced in the current implementation
if one or more of following conditions are true:
- The soft heap limit is set to zero.
- Memory accounting is disabled using a combination of the
sqlite3_config
(SQLITE_CONFIG_MEMSTATUS
,...) start-time option and
the SQLITE_DEFAULT_MEMSTATUS
compile-time option.
- An alternative page cache implementation is specified using
sqlite3_config
(SQLITE_CONFIG_PCACHE2
,...).
- The page cache allocates from its own memory pool supplied
by sqlite3_config
(SQLITE_CONFIG_PAGECACHE
,...) rather than
from the heap.
Beginning with SQLite version 3.7.3, the soft heap limit is enforced
regardless of whether or not the SQLITE_ENABLE_MEMORY_MANAGEMENT
compile-time option is invoked. With SQLITE_ENABLE_MEMORY_MANAGEMENT
,
the soft heap limit is enforced on every memory allocation. Without
SQLITE_ENABLE_MEMORY_MANAGEMENT
, the soft heap limit is only enforced
when memory is allocated by the page cache. Testing suggests that because
the page cache is the predominate memory user in SQLite, most
applications will achieve adequate soft heap limit enforcement without
the use of SQLITE_ENABLE_MEMORY_MANAGEMENT
.
The circumstances under which SQLite will enforce the soft heap limit may
changes in future releases of SQLite.
Retrieving Statement SQL
const char *sqlite3_sql(sqlite3_stmt *pStmt);
This interface can be used to retrieve a saved copy of the original
SQL text used to create a prepared statement
if that statement was
compiled using either sqlite3_prepare_v2()
or sqlite3_prepare16_v2()
.
SQLite Runtime Status
int sqlite3_status(int op, int *pCurrent, int *pHighwater, int resetFlag);
This interface is used to retrieve runtime status information
about the performance of SQLite, and optionally to reset various
highwater marks. The first argument is an integer code for
the specific parameter to measure. Recognized integer codes
are of the form SQLITE_STATUS_...
.
The current value of the parameter is returned into *pCurrent.
The highest recorded value is returned in *pHighwater. If the
resetFlag is true, then the highest record value is reset after
*pHighwater is written. Some parameters do not record the highest
value. For those parameters
nothing is written into *pHighwater and the resetFlag is ignored.
Other parameters record only the highwater mark and not the current
value. For these latter parameters nothing is written into *pCurrent.
The sqlite3_status() routine returns SQLITE_OK on success and a
non-zero error code
on failure.
This routine is threadsafe but is not atomic. This routine can be
called while other threads are running the same or different SQLite
interfaces. However the values returned in *pCurrent and
*pHighwater reflect the status of SQLite at different points in time
and it is possible that another thread might change the parameter
in between the times when *pCurrent and *pHighwater are written.
See also: sqlite3_db_status()
Evaluate An SQL Statement
int sqlite3_step(sqlite3_stmt*);
After a prepared statement
has been prepared using either
sqlite3_prepare_v2()
or sqlite3_prepare16_v2()
or one of the legacy
interfaces sqlite3_prepare()
or sqlite3_prepare16()
, this function
must be called one or more times to evaluate the statement.
The details of the behavior of the sqlite3_step() interface depend
on whether the statement was prepared using the newer "v2" interface
sqlite3_prepare_v2()
and sqlite3_prepare16_v2()
or the older legacy
interface sqlite3_prepare()
and sqlite3_prepare16()
. The use of the
new "v2" interface is recommended for new applications but the legacy
interface will continue to be supported.
In the legacy interface, the return value will be either SQLITE_BUSY
,
SQLITE_DONE
, SQLITE_ROW
, SQLITE_ERROR
, or SQLITE_MISUSE
.
With the "v2" interface, any of the other result codes
or
extended result codes
might be returned as well.
SQLITE_BUSY
means that the database engine was unable to acquire the
database locks it needs to do its job. If the statement is a COMMIT
or occurs outside of an explicit transaction, then you can retry the
statement. If the statement is not a COMMIT
and occurs within an
explicit transaction then you should rollback the transaction before
continuing.
SQLITE_DONE
means that the statement has finished executing
successfully. sqlite3_step() should not be called again on this virtual
machine without first calling sqlite3_reset()
to reset the virtual
machine back to its initial state.
If the SQL statement being executed returns any data, then SQLITE_ROW
is returned each time a new row of data is ready for processing by the
caller. The values may be accessed using the column access functions
.
sqlite3_step() is called again to retrieve the next row of data.
SQLITE_ERROR
means that a run-time error (such as a constraint
violation) has occurred. sqlite3_step() should not be called again on
the VM. More information may be found by calling sqlite3_errmsg()
.
With the legacy interface, a more specific error code (for example,
SQLITE_INTERRUPT
, SQLITE_SCHEMA
, SQLITE_CORRUPT
, and so forth)
can be obtained by calling sqlite3_reset()
on the
prepared statement
. In the "v2" interface,
the more specific error code is returned directly by sqlite3_step().
SQLITE_MISUSE
means that the this routine was called inappropriately.
Perhaps it was called on a prepared statement
that has
already been finalized
or on one that had
previously returned SQLITE_ERROR
or SQLITE_DONE
. Or it could
be the case that the same database connection is being used by two or
more threads at the same moment in time.
For all versions of SQLite up to and including 3.6.23.1, a call to
sqlite3_reset()
was required after sqlite3_step() returned anything
other than SQLITE_ROW
before any subsequent invocation of
sqlite3_step(). Failure to reset the prepared statement using
sqlite3_reset()
would result in an SQLITE_MISUSE
return from
sqlite3_step(). But after version 3.6.23.1, sqlite3_step() began
calling sqlite3_reset()
automatically in this circumstance rather
than returning SQLITE_MISUSE
. This is not considered a compatibility
break because any application that ever receives an SQLITE_MISUSE error
is broken by definition. The SQLITE_OMIT_AUTORESET
compile-time option
can be used to restore the legacy behavior.
Goofy Interface Alert:
In the legacy interface, the sqlite3_step()
API always returns a generic error code, SQLITE_ERROR
, following any
error other than SQLITE_BUSY
and SQLITE_MISUSE
. You must call
sqlite3_reset()
or sqlite3_finalize()
in order to find one of the
specific error codes
that better describes the error.
We admit that this is a goofy design. The problem has been fixed
with the "v2" interface. If you prepare all of your SQL statements
using either sqlite3_prepare_v2()
or sqlite3_prepare16_v2()
instead
of the legacy sqlite3_prepare()
and sqlite3_prepare16()
interfaces,
then the more specific error codes
are returned directly
by sqlite3_step(). The use of the "v2" interface is recommended.
Determine If A Prepared Statement Has Been Reset
int sqlite3_stmt_busy(sqlite3_stmt*);
The sqlite3_stmt_busy(S) interface returns true (non-zero) if the
prepared statement
S has been stepped at least once using
sqlite3_step(S)
but has not run to completion and/or has not
been reset using sqlite3_reset(S)
. The sqlite3_stmt_busy(S)
interface returns false if S is a NULL pointer. If S is not a
NULL pointer and is not a pointer to a valid prepared statement
object, then the behavior is undefined and probably undesirable.
This interface can be used in combination sqlite3_next_stmt()
to locate all prepared statements associated with a database
connection that are in need of being reset. This can be used,
for example, in diagnostic routines to search for prepared
statements that are holding a transaction open.
Determine If An SQL Statement Writes The Database
int sqlite3_stmt_readonly(sqlite3_stmt *pStmt);
The sqlite3_stmt_readonly(X) interface returns true (non-zero) if
and only if the prepared statement
X makes no direct changes to
the content of the database file.
Note that application-defined SQL functions
or
virtual tables
might change the database indirectly as a side effect.
For example, if an application defines a function "eval()" that
calls sqlite3_exec()
, then the following SQL statement would
change the database file through side-effects:
SELECT eval('DELETE FROM t1') FROM t2;
But because the SELECT
statement does not change the database file
directly, sqlite3_stmt_readonly() would still return true.
Transaction control statements such as BEGIN
, COMMIT
, ROLLBACK
,
SAVEPOINT
, and RELEASE
cause sqlite3_stmt_readonly() to return true,
since the statements themselves do not actually modify the database but
rather they control the timing of when other statements modify the
database. The ATTACH
and DETACH
statements also cause
sqlite3_stmt_readonly() to return true since, while those statements
change the configuration of a database connection, they do not make
changes to the content of the database files on disk.
Prepared Statement Status
int sqlite3_stmt_status(sqlite3_stmt*, int op,int resetFlg);
Each prepared statement maintains various
SQLITE_STMTSTATUS counters
that measure the number
of times it has performed specific operations. These counters can
be used to monitor the performance characteristics of the prepared
statements. For example, if the number of table steps greatly exceeds
the number of table searches or result rows, that would tend to indicate
that the prepared statement is using a full table scan rather than
an index.
This interface is used to retrieve and reset counter values from
a prepared statement
. The first argument is the prepared statement
object to be interrogated. The second argument
is an integer code for a specific SQLITE_STMTSTATUS counter
to be interrogated.
The current value of the requested counter is returned.
If the resetFlg is true, then the counter is reset to zero after this
interface call returns.
See also: sqlite3_status()
and sqlite3_db_status()
.
String Comparison
int sqlite3_strnicmp(const char *, const char *, int);
The sqlite3_strnicmp()
API allows applications and extensions to
compare the contents of two buffers containing UTF-8 strings in a
case-independent fashion, using the same definition of case independence
that SQLite uses internally when comparing identifiers.
Extract Metadata About A Column Of A Table
int sqlite3_table_column_metadata(
sqlite3 *db, /* Connection handle */
const char *zDbName, /* Database name or NULL */
const char *zTableName, /* Table name */
const char *zColumnName, /* Column name */
char const **pzDataType, /* OUTPUT: Declared data type */
char const **pzCollSeq, /* OUTPUT: Collation sequence name */
int *pNotNull, /* OUTPUT: True if NOT NULL constraint exists */
int *pPrimaryKey, /* OUTPUT: True if column part of PK */
int *pAutoinc /* OUTPUT: True if column is auto-increment */
);
This routine returns metadata about a specific column of a specific
database table accessible using the database connection
handle
passed as the first function argument.
The column is identified by the second, third and fourth parameters to
this function. The second parameter is either the name of the database
(i.e. "main", "temp", or an attached database) containing the specified
table or NULL. If it is NULL, then all attached databases are searched
for the table using the same algorithm used by the database engine to
resolve unqualified table references.
The third and fourth parameters to this function are the table and column
name of the desired column, respectively. Neither of these parameters
may be NULL.
Metadata is returned by writing to the memory locations passed as the 5th
and subsequent parameters to this function. Any of these arguments may be
NULL, in which case the corresponding element of metadata is omitted.
Parameter
Output
Type
Description
5th
const char*
Data type
6th
const char*
Name of default collation sequence
7th
int
True if column has a NOT NULL constraint
8th
int
True if column is part of the PRIMARY KEY
9th
int
True if column is AUTOINCREMENT
The memory pointed to by the character pointers returned for the
declaration type and collation sequence is valid only until the next
call to any SQLite API function.
If the specified table is actually a view, an error code
is returned.
If the specified column is "rowid", "oid" or "_rowid_" and an
INTEGER PRIMARY KEY
column has been explicitly declared, then the output
parameters are set for the explicitly declared column. If there is no
explicitly declared INTEGER PRIMARY KEY
column, then the output
parameters are set as follows:
data type: "INTEGER"
collation sequence: "BINARY"
not null: 0
primary key: 1
auto increment: 0
This function may load one or more schemas from database files. If an
error occurs during this process, or if the requested table or column
cannot be found, an error code
is returned and an error message left
in the database connection
(to be retrieved using sqlite3_errmsg()).
This API is only available if the library was compiled with the
SQLITE_ENABLE_COLUMN_METADATA
C-preprocessor symbol defined.
Testing Interface
int sqlite3_test_control(int op, ...);
The sqlite3_test_control() interface is used to read out internal
state of SQLite and to inject faults into SQLite for testing
purposes. The first parameter is an operation code that determines
the number, meaning, and operation of all subsequent parameters.
This interface is not for use by applications. It exists solely
for verifying the correct operation of the SQLite library. Depending
on how the SQLite library is compiled, this interface might not exist.
The details of the operation codes, their meanings, the parameters
they take, and what they do are all subject to change without notice.
Unlike most of the SQLite API, this function is not guaranteed to
operate consistently from one release to the next.
Test To See If The Library Is Threadsafe
int sqlite3_threadsafe(void);
The sqlite3_threadsafe() function returns zero if and only if
SQLite was compiled with mutexing code omitted due to the
SQLITE_THREADSAFE
compile-time option being set to 0.
SQLite can be compiled with or without mutexes. When
the SQLITE_THREADSAFE
C preprocessor macro is 1 or 2, mutexes
are enabled and SQLite is threadsafe. When the
SQLITE_THREADSAFE
macro is 0,
the mutexes are omitted. Without the mutexes, it is not safe
to use SQLite concurrently from more than one thread.
Enabling mutexes incurs a measurable performance penalty.
So if speed is of utmost importance, it makes sense to disable
the mutexes. But for maximum safety, mutexes should be enabled.
The default behavior is for mutexes to be enabled.
This interface can be used by an application to make sure that the
version of SQLite that it is linking against was compiled with
the desired setting of the SQLITE_THREADSAFE
macro.
This interface only reports on the compile-time mutex setting
of the SQLITE_THREADSAFE
flag. If SQLite is compiled with
SQLITE_THREADSAFE=1 or =2 then mutexes are enabled by default but
can be fully or partially disabled using a call to sqlite3_config()
with the verbs SQLITE_CONFIG_SINGLETHREAD
, SQLITE_CONFIG_MULTITHREAD
,
or SQLITE_CONFIG_MUTEX
. The return value of the
sqlite3_threadsafe() function shows only the compile-time setting of
thread safety, not any run-time changes to that setting made by
sqlite3_config(). In other words, the return value from sqlite3_threadsafe()
is unchanged by calls to sqlite3_config().
See the threading mode
documentation for additional information.
Total Number Of Rows Modified
int sqlite3_total_changes(sqlite3*);
This function returns the number of row changes caused by INSERT
,
UPDATE
or DELETE
statements since the database connection
was opened.
The count returned by sqlite3_total_changes() includes all changes
from all trigger
contexts and changes made by
foreign key actions
. However,
the count does not include changes used to implement REPLACE
constraints,
do rollbacks or ABORT processing, or DROP TABLE
processing. The
count does not include rows of views that fire an INSTEAD OF trigger
,
though if the INSTEAD OF trigger makes changes of its own, those changes
are counted.
The sqlite3_total_changes() function counts the changes as soon as
the statement that makes them is completed (when the statement handle
is passed to sqlite3_reset()
or sqlite3_finalize()
).
See also the sqlite3_changes()
interface, the
count_changes pragma
, and the total_changes() SQL function
.
If a separate thread makes changes on the same database connection
while sqlite3_total_changes()
is running then the value
returned is unpredictable and not meaningful.
Unlock Notification
int sqlite3_unlock_notify(
sqlite3 *pBlocked, /* Waiting connection */
void (*xNotify)(void **apArg, int nArg), /* Callback function to invoke */
void *pNotifyArg /* Argument to pass to xNotify */
);
When running in shared-cache mode, a database operation may fail with
an SQLITE_LOCKED
error if the required locks on the shared-cache or
individual tables within the shared-cache cannot be obtained. See
SQLite Shared-Cache Mode
for a description of shared-cache locking.
This API may be used to register a callback that SQLite will invoke
when the connection currently holding the required lock relinquishes it.
This API is only available if the library was compiled with the
SQLITE_ENABLE_UNLOCK_NOTIFY
C-preprocessor symbol defined.
See Also: Using the SQLite Unlock Notification Feature
.
Shared-cache locks are released when a database connection concludes
its current transaction, either by committing it or rolling it back.
When a connection (known as the blocked connection) fails to obtain a
shared-cache lock and SQLITE_LOCKED is returned to the caller, the
identity of the database connection (the blocking connection) that
has locked the required resource is stored internally. After an
application receives an SQLITE_LOCKED error, it may call the
sqlite3_unlock_notify() method with the blocked connection handle as
the first argument to register for a callback that will be invoked
when the blocking connections current transaction is concluded. The
callback is invoked from within the sqlite3_step
or sqlite3_close
call that concludes the blocking connections transaction.
If sqlite3_unlock_notify() is called in a multi-threaded application,
there is a chance that the blocking connection will have already
concluded its transaction by the time sqlite3_unlock_notify() is invoked.
If this happens, then the specified callback is invoked immediately,
from within the call to sqlite3_unlock_notify().
If the blocked connection is attempting to obtain a write-lock on a
shared-cache table, and more than one other connection currently holds
a read-lock on the same table, then SQLite arbitrarily selects one of
the other connections to use as the blocking connection.
There may be at most one unlock-notify callback registered by a
blocked connection. If sqlite3_unlock_notify() is called when the
blocked connection already has a registered unlock-notify callback,
then the new callback replaces the old. If sqlite3_unlock_notify() is
called with a NULL pointer as its second argument, then any existing
unlock-notify callback is canceled. The blocked connections
unlock-notify callback may also be canceled by closing the blocked
connection using sqlite3_close()
.
The unlock-notify callback is not reentrant. If an application invokes
any sqlite3_xxx API functions from within an unlock-notify callback, a
crash or deadlock may be the result.
Unless deadlock is detected (see below), sqlite3_unlock_notify() always
returns SQLITE_OK.
Callback Invocation Details
When an unlock-notify callback is registered, the application provides a
single void* pointer that is passed to the callback when it is invoked.
However, the signature of the callback function allows SQLite to pass
it an array of void* context pointers. The first argument passed to
an unlock-notify callback is a pointer to an array of void* pointers,
and the second is the number of entries in the array.
When a blocking connections transaction is concluded, there may be
more than one blocked connection that has registered for an unlock-notify
callback. If two or more such blocked connections have specified the
same callback function, then instead of invoking the callback function
multiple times, it is invoked once with the set of void* context pointers
specified by the blocked connections bundled together into an array.
This gives the application an opportunity to prioritize any actions
related to the set of unblocked database connections.
Deadlock Detection
Assuming that after registering for an unlock-notify callback a
database waits for the callback to be issued before taking any further
action (a reasonable assumption), then using this API may cause the
application to deadlock. For example, if connection X is waiting for
connection Y's transaction to be concluded, and similarly connection
Y is waiting on connection X's transaction, then neither connection
will proceed and the system may remain deadlocked indefinitely.
To avoid this scenario, the sqlite3_unlock_notify() performs deadlock
detection. If a given call to sqlite3_unlock_notify() would put the
system in a deadlocked state, then SQLITE_LOCKED is returned and no
unlock-notify callback is registered. The system is said to be in
a deadlocked state if connection A has registered for an unlock-notify
callback on the conclusion of connection B's transaction, and connection
B has itself registered for an unlock-notify callback when connection
A's transaction is concluded. Indirect deadlock is also detected, so
the system is also considered to be deadlocked if connection B has
registered for an unlock-notify callback on the conclusion of connection
C's transaction, where connection C is waiting on connection A. Any
number of levels of indirection are allowed.
The "DROP TABLE" Exception
When a call to sqlite3_step()
returns SQLITE_LOCKED, it is almost
always appropriate to call sqlite3_unlock_notify(). There is however,
one exception. When executing a "DROP TABLE" or "DROP INDEX" statement,
SQLite checks if there are any currently executing SELECT statements
that belong to the same connection. If there are, SQLITE_LOCKED is
returned. In this case there is no "blocking connection", so invoking
sqlite3_unlock_notify() results in the unlock-notify callback being
invoked immediately. If the application then re-attempts the "DROP TABLE"
or "DROP INDEX" query, an infinite loop might be the result.
One way around this problem is to check the extended error code returned
by an sqlite3_step() call. If there is a blocking connection, then the
extended error code is set to SQLITE_LOCKED_SHAREDCACHE. Otherwise, in
the special "DROP TABLE/INDEX" case, the extended error code is just
SQLITE_LOCKED.
Data Change Notification Callbacks
void *sqlite3_update_hook(
sqlite3*,
void(*)(void *,int ,char const *,char const *,sqlite3_int64),
void*
);
The sqlite3_update_hook() interface registers a callback function
with the database connection
identified by the first argument
to be invoked whenever a row is updated, inserted or deleted.
Any callback set by a previous call to this function
for the same database connection is overridden.
The second argument is a pointer to the function to invoke when a
row is updated, inserted or deleted.
The first argument to the callback is a copy of the third argument
to sqlite3_update_hook().
The second callback argument is one of SQLITE_INSERT
, SQLITE_DELETE
,
or SQLITE_UPDATE
, depending on the operation that caused the callback
to be invoked.
The third and fourth arguments to the callback contain pointers to the
database and table name containing the affected row.
The final callback parameter is the rowid
of the row.
In the case of an update, this is the rowid
after the update takes place.
The update hook is not invoked when internal system tables are
modified (i.e. sqlite_master and sqlite_sequence).
In the current implementation, the update hook
is not invoked when duplication rows are deleted because of an
ON CONFLICT REPLACE
clause. Nor is the update hook
invoked when rows are deleted using the truncate optimization
.
The exceptions defined in this paragraph might change in a future
release of SQLite.
The update hook implementation must not do anything that will modify
the database connection that invoked the update hook. Any actions
to modify the database connection must be deferred until after the
completion of the sqlite3_step()
call that triggered the update hook.
Note that sqlite3_prepare_v2()
and sqlite3_step()
both modify their
database connections for the meaning of "modify" in this paragraph.
The sqlite3_update_hook(D,C,P) function
returns the P argument from the previous call
on the same database connection
D, or NULL for
the first call on D.
See also the sqlite3_commit_hook()
and sqlite3_rollback_hook()
interfaces.
User Data For Functions
void *sqlite3_user_data(sqlite3_context*);
The sqlite3_user_data() interface returns a copy of
the pointer that was the pUserData parameter (the 5th parameter)
of the sqlite3_create_function()
and sqlite3_create_function16()
routines that originally
registered the application defined function.
This routine must be called from the same thread in which
the application-defined function is running.
Virtual Table Interface Configuration
int sqlite3_vtab_config(sqlite3*, int op, ...);
This function may be called by either the xConnect
or xCreate
method
of a virtual table
implementation to configure
various facets of the virtual table interface.
If this interface is invoked outside the context of an xConnect or
xCreate virtual table method then the behavior is undefined.
At present, there is only one option that may be configured using
this function. (See SQLITE_VTAB_CONSTRAINT_SUPPORT
.) Further options
may be added in the future.
Determine The Virtual Table Conflict Policy
int sqlite3_vtab_on_conflict(sqlite3 *);
This function may only be called from within a call to the xUpdate
method
of a virtual table
implementation for an INSERT or UPDATE operation. The
value returned is one of SQLITE_ROLLBACK
, SQLITE_IGNORE
, SQLITE_FAIL
,
SQLITE_ABORT
, or SQLITE_REPLACE
, according to the ON CONFLICT
mode
of the SQL statement that triggered the call to the xUpdate
method of the
virtual table
.
Configure an auto-checkpoint
int sqlite3_wal_autocheckpoint(sqlite3 *db, int N);
The sqlite3_wal_autocheckpoint(D,N)
is a wrapper around
sqlite3_wal_hook()
that causes any database on database connection
D
to automatically checkpoint
after committing a transaction if there are N or
more frames in the write-ahead log
file. Passing zero or
a negative value as the nFrame parameter disables automatic
checkpoints entirely.
The callback registered by this function replaces any existing callback
registered using sqlite3_wal_hook()
. Likewise, registering a callback
using sqlite3_wal_hook()
disables the automatic checkpoint mechanism
configured by this function.
The wal_autocheckpoint pragma
can be used to invoke this interface
from SQL.
Every new database connection
defaults to having the auto-checkpoint
enabled with a threshold of 1000 or SQLITE_DEFAULT_WAL_AUTOCHECKPOINT
pages. The use of this interface
is only necessary if the default setting is found to be suboptimal
for a particular application.
Checkpoint a database
int sqlite3_wal_checkpoint(sqlite3 *db, const char *zDb);
The sqlite3_wal_checkpoint(D,X)
interface causes database named X
on database connection
D to be checkpointed
. If X is NULL or an
empty string, then a checkpoint is run on all databases of
connection D. If the database connection D is not in
write-ahead log mode
then this interface is a harmless no-op.
The wal_checkpoint pragma
can be used to invoke this interface
from SQL. The sqlite3_wal_autocheckpoint()
interface and the
wal_autocheckpoint pragma
can be used to cause this interface to be
run whenever the WAL reaches a certain size threshold.
See also: sqlite3_wal_checkpoint_v2()
Checkpoint a database
int sqlite3_wal_checkpoint_v2(
sqlite3 *db, /* Database handle */
const char *zDb, /* Name of attached database (or NULL) */
int eMode, /* SQLITE_CHECKPOINT_* value */
int *pnLog, /* OUT: Size of WAL log in frames */
int *pnCkpt /* OUT: Total number of frames checkpointed */
);
Run a checkpoint operation on WAL database zDb attached to database
handle db. The specific operation is determined by the value of the
eMode parameter:
SQLITE_CHECKPOINT_PASSIVE
Checkpoint as many frames as possible without waiting for any database
readers or writers to finish. Sync the db file if all frames in the log
are checkpointed. This mode is the same as calling
sqlite3_wal_checkpoint(). The busy-handler callback is never invoked.
SQLITE_CHECKPOINT_FULL
This mode blocks (calls the busy-handler callback) until there is no
database writer and all readers are reading from the most recent database
snapshot. It then checkpoints all frames in the log file and syncs the
database file. This call blocks database writers while it is running,
but not database readers.
SQLITE_CHECKPOINT_RESTART
This mode works the same way as SQLITE_CHECKPOINT_FULL, except after
checkpointing the log file it blocks (calls the busy-handler callback)
until all readers are reading from the database file only. This ensures
that the next client to write to the database file restarts the log file
from the beginning. This call blocks database writers while it is running,
but not database readers.
If pnLog is not NULL, then *pnLog is set to the total number of frames in
the log file before returning. If pnCkpt is not NULL, then *pnCkpt is set to
the total number of checkpointed frames (including any that were already
checkpointed when this function is called). *pnLog and *pnCkpt may be
populated even if sqlite3_wal_checkpoint_v2() returns other than SQLITE_OK.
If no values are available because of an error, they are both set to -1
before returning to communicate this to the caller.
All calls obtain an exclusive "checkpoint" lock on the database file. If
any other process is running a checkpoint operation at the same time, the
lock cannot be obtained and SQLITE_BUSY is returned. Even if there is a
busy-handler configured, it will not be invoked in this case.
The SQLITE_CHECKPOINT_FULL and RESTART modes also obtain the exclusive
"writer" lock on the database file. If the writer lock cannot be obtained
immediately, and a busy-handler is configured, it is invoked and the writer
lock retried until either the busy-handler returns 0 or the lock is
successfully obtained. The busy-handler is also invoked while waiting for
database readers as described above. If the busy-handler returns 0 before
the writer lock is obtained or while waiting for database readers, the
checkpoint operation proceeds from that point in the same way as
SQLITE_CHECKPOINT_PASSIVE - checkpointing as many frames as possible
without blocking any further. SQLITE_BUSY is returned in this case.
If parameter zDb is NULL or points to a zero length string, then the
specified operation is attempted on all WAL databases. In this case the
values written to output parameters *pnLog and *pnCkpt are undefined. If
an SQLITE_BUSY error is encountered when processing one or more of the
attached WAL databases, the operation is still attempted on any remaining
attached databases and SQLITE_BUSY is returned to the caller. If any other
error occurs while processing an attached database, processing is abandoned
and the error code returned to the caller immediately. If no error
(SQLITE_BUSY or otherwise) is encountered while processing the attached
databases, SQLITE_OK is returned.
If database zDb is the name of an attached database that is not in WAL
mode, SQLITE_OK is returned and both *pnLog and *pnCkpt set to -1. If
zDb is not NULL (or a zero length string) and is not the name of any
attached database, SQLITE_ERROR is returned to the caller.
Write-Ahead Log Commit Hook
void *sqlite3_wal_hook(
sqlite3*,
int(*)(void *,sqlite3*,const char*,int),
void*
);
The sqlite3_wal_hook()
function is used to register a callback that
will be invoked each time a database connection commits data to a
write-ahead log
(i.e. whenever a transaction is committed in
journal_mode=WAL mode
).
The callback is invoked by SQLite after the commit has taken place and
the associated write-lock on the database released, so the implementation
may read, write or checkpoint
the database as required.
The first parameter passed to the callback function when it is invoked
is a copy of the third parameter passed to sqlite3_wal_hook() when
registering the callback. The second is a copy of the database handle.
The third parameter is the name of the database that was written to -
either "main" or the name of an ATTACH
-ed database. The fourth parameter
is the number of pages currently in the write-ahead log file,
including those that were just committed.
The callback function should normally return SQLITE_OK
. If an error
code is returned, that error will propagate back up through the
SQLite code base to cause the statement that provoked the callback
to report an error, though the commit will have still occurred. If the
callback returns SQLITE_ROW
or SQLITE_DONE
, or if it returns a value
that does not correspond to any valid SQLite error code, the results
are undefined.
A single database handle may have at most a single write-ahead log callback
registered at one time. Calling sqlite3_wal_hook()
replaces any
previously registered write-ahead log callback. Note that the
sqlite3_wal_autocheckpoint()
interface and the
wal_autocheckpoint pragma
both invoke sqlite3_wal_hook()
and will
those overwrite any prior sqlite3_wal_hook()
settings.
Result Codes
#define SQLITE_OK 0 /* Successful result */
/* beginning-of-error-codes */
#define SQLITE_ERROR 1 /* SQL error or missing database */
#define SQLITE_INTERNAL 2 /* Internal logic error in SQLite */
#define SQLITE_PERM 3 /* Access permission denied */
#define SQLITE_ABORT 4 /* Callback routine requested an abort */
#define SQLITE_BUSY 5 /* The database file is locked */
#define SQLITE_LOCKED 6 /* A table in the database is locked */
#define SQLITE_NOMEM 7 /* A malloc() failed */
#define SQLITE_READONLY 8 /* Attempt to write a readonly database */
#define SQLITE_INTERRUPT 9 /* Operation terminated by sqlite3_interrupt()*/
#define SQLITE_IOERR 10 /* Some kind of disk I/O error occurred */
#define SQLITE_CORRUPT 11 /* The database disk image is malformed */
#define SQLITE_NOTFOUND 12 /* Unknown opcode in sqlite3_file_control() */
#define SQLITE_FULL 13 /* Insertion failed because database is full */
#define SQLITE_CANTOPEN 14 /* Unable to open the database file */
#define SQLITE_PROTOCOL 15 /* Database lock protocol error */
#define SQLITE_EMPTY 16 /* Database is empty */
#define SQLITE_SCHEMA 17 /* The database schema changed */
#define SQLITE_TOOBIG 18 /* String or BLOB exceeds size limit */
#define SQLITE_CONSTRAINT 19 /* Abort due to constraint violation */
#define SQLITE_MISMATCH 20 /* Data type mismatch */
#define SQLITE_MISUSE 21 /* Library used incorrectly */
#define SQLITE_NOLFS 22 /* Uses OS features not supported on host */
#define SQLITE_AUTH 23 /* Authorization denied */
#define SQLITE_FORMAT 24 /* Auxiliary database format error */
#define SQLITE_RANGE 25 /* 2nd parameter to sqlite3_bind out of range */
#define SQLITE_NOTADB 26 /* File opened that is not a database file */
#define SQLITE_ROW 100 /* sqlite3_step() has another row ready */
#define SQLITE_DONE 101 /* sqlite3_step() has finished executing */
/* end-of-error-codes */
Many SQLite functions return an integer result code from the set shown
here in order to indicate success or failure.
New error codes may be added in future versions of SQLite.
See also: extended result codes
,
sqlite3_vtab_on_conflict()
result codes
.
Flags for the xAccess VFS method
#define SQLITE_ACCESS_EXISTS 0
#define SQLITE_ACCESS_READWRITE 1 /* Used by PRAGMA temp_store_directory */
#define SQLITE_ACCESS_READ 2 /* Unused */
These integer constants can be used as the third parameter to
the xAccess method of an sqlite3_vfs
object. They determine
what kind of permissions the xAccess method is looking for.
With SQLITE_ACCESS_EXISTS, the xAccess method
simply checks whether the file exists.
With SQLITE_ACCESS_READWRITE, the xAccess method
checks whether the named directory is both readable and writable
(in other words, if files can be added, removed, and renamed within
the directory).
The SQLITE_ACCESS_READWRITE constant is currently used only by the
temp_store_directory pragma
, though this could change in a future
release of SQLite.
With SQLITE_ACCESS_READ, the xAccess method
checks whether the file is readable. The SQLITE_ACCESS_READ constant is
currently unused, though it might be used in a future release of
SQLite.
Authorizer Action Codes
/******************************************* 3rd ************ 4th ***********/
#define SQLITE_CREATE_INDEX 1 /* Index Name Table Name */
#define SQLITE_CREATE_TABLE 2 /* Table Name NULL */
#define SQLITE_CREATE_TEMP_INDEX 3 /* Index Name Table Name */
#define SQLITE_CREATE_TEMP_TABLE 4 /* Table Name NULL */
#define SQLITE_CREATE_TEMP_TRIGGER 5 /* Trigger Name Table Name */
#define SQLITE_CREATE_TEMP_VIEW 6 /* View Name NULL */
#define SQLITE_CREATE_TRIGGER 7 /* Trigger Name Table Name */
#define SQLITE_CREATE_VIEW 8 /* View Name NULL */
#define SQLITE_DELETE 9 /* Table Name NULL */
#define SQLITE_DROP_INDEX 10 /* Index Name Table Name */
#define SQLITE_DROP_TABLE 11 /* Table Name NULL */
#define SQLITE_DROP_TEMP_INDEX 12 /* Index Name Table Name */
#define SQLITE_DROP_TEMP_TABLE 13 /* Table Name NULL */
#define SQLITE_DROP_TEMP_TRIGGER 14 /* Trigger Name Table Name */
#define SQLITE_DROP_TEMP_VIEW 15 /* View Name NULL */
#define SQLITE_DROP_TRIGGER 16 /* Trigger Name Table Name */
#define SQLITE_DROP_VIEW 17 /* View Name NULL */
#define SQLITE_INSERT 18 /* Table Name NULL */
#define SQLITE_PRAGMA 19 /* Pragma Name 1st arg or NULL */
#define SQLITE_READ 20 /* Table Name Column Name */
#define SQLITE_SELECT 21 /* NULL NULL */
#define SQLITE_TRANSACTION 22 /* Operation NULL */
#define SQLITE_UPDATE 23 /* Table Name Column Name */
#define SQLITE_ATTACH 24 /* Filename NULL */
#define SQLITE_DETACH 25 /* Database Name NULL */
#define SQLITE_ALTER_TABLE 26 /* Database Name Table Name */
#define SQLITE_REINDEX 27 /* Index Name NULL */
#define SQLITE_ANALYZE 28 /* Table Name NULL */
#define SQLITE_CREATE_VTABLE 29 /* Table Name Module Name */
#define SQLITE_DROP_VTABLE 30 /* Table Name Module Name */
#define SQLITE_FUNCTION 31 /* NULL Function Name */
#define SQLITE_SAVEPOINT 32 /* Operation Savepoint Name */
#define SQLITE_COPY 0 /* No longer used */
The sqlite3_set_authorizer()
interface registers a callback function
that is invoked to authorize certain SQL statement actions. The
second parameter to the callback is an integer code that specifies
what action is being authorized. These are the integer action codes that
the authorizer callback may be passed.
These action code values signify what kind of operation is to be
authorized. The 3rd and 4th parameters to the authorization
callback function will be parameters or NULL depending on which of these
codes is used as the second parameter. The 5th parameter to the
authorizer callback is the name of the database ("main", "temp",
etc.) if applicable. The 6th parameter to the authorizer callback
is the name of the inner-most trigger or view that is responsible for
the access attempt or NULL if this access attempt is directly from
top-level SQL code.
Text Encodings
#define SQLITE_UTF8 1
#define SQLITE_UTF16LE 2
#define SQLITE_UTF16BE 3
#define SQLITE_UTF16 4 /* Use native byte order */
#define SQLITE_ANY 5 /* sqlite3_create_function only */
#define SQLITE_UTF16_ALIGNED 8 /* sqlite3_create_collation only */
These constant define integer codes that represent the various
text encodings supported by SQLite.
Fundamental Datatypes
#define SQLITE_INTEGER 1
#define SQLITE_FLOAT 2
#define SQLITE_BLOB 4
#define SQLITE_NULL 5
#ifdef SQLITE_TEXT
# undef SQLITE_TEXT
#else
# define SQLITE_TEXT 3
#endif
#define SQLITE3_TEXT 3
Every value in SQLite has one of five fundamental datatypes:
- 64-bit signed integer
- 64-bit IEEE floating point number
- string
- BLOB
- NULL
These constants are codes for each of those types.
Note that the SQLITE_TEXT constant was also used in SQLite version 2
for a completely different meaning. Software that links against both
SQLite version 2 and SQLite version 3 should use SQLITE3_TEXT, not
SQLITE_TEXT.
Extended Result Codes
#define SQLITE_IOERR_READ (SQLITE_IOERR | (1<<8))
#define SQLITE_IOERR_SHORT_READ (SQLITE_IOERR | (2<<8))
#define SQLITE_IOERR_WRITE (SQLITE_IOERR | (3<<8))
#define SQLITE_IOERR_FSYNC (SQLITE_IOERR | (4<<8))
#define SQLITE_IOERR_DIR_FSYNC (SQLITE_IOERR | (5<<8))
#define SQLITE_IOERR_TRUNCATE (SQLITE_IOERR | (6<<8))
#define SQLITE_IOERR_FSTAT (SQLITE_IOERR | (7<<8))
#define SQLITE_IOERR_UNLOCK (SQLITE_IOERR | (8<<8))
#define SQLITE_IOERR_RDLOCK (SQLITE_IOERR | (9<<8))
#define SQLITE_IOERR_DELETE (SQLITE_IOERR | (10<<8))
#define SQLITE_IOERR_BLOCKED (SQLITE_IOERR | (11<<8))
#define SQLITE_IOERR_NOMEM (SQLITE_IOERR | (12<<8))
#define SQLITE_IOERR_ACCESS (SQLITE_IOERR | (13<<8))
#define SQLITE_IOERR_CHECKRESERVEDLOCK (SQLITE_IOERR | (14<<8))
#define SQLITE_IOERR_LOCK (SQLITE_IOERR | (15<<8))
#define SQLITE_IOERR_CLOSE (SQLITE_IOERR | (16<<8))
#define SQLITE_IOERR_DIR_CLOSE (SQLITE_IOERR | (17<<8))
#define SQLITE_IOERR_SHMOPEN (SQLITE_IOERR | (18<<8))
#define SQLITE_IOERR_SHMSIZE (SQLITE_IOERR | (19<<8))
#define SQLITE_IOERR_SHMLOCK (SQLITE_IOERR | (20<<8))
#define SQLITE_IOERR_SHMMAP (SQLITE_IOERR | (21<<8))
#define SQLITE_IOERR_SEEK (SQLITE_IOERR | (22<<8))
#define SQLITE_LOCKED_SHAREDCACHE (SQLITE_LOCKED | (1<<8))
#define SQLITE_BUSY_RECOVERY (SQLITE_BUSY | (1<<8))
#define SQLITE_CANTOPEN_NOTEMPDIR (SQLITE_CANTOPEN | (1<<8))
#define SQLITE_CORRUPT_VTAB (SQLITE_CORRUPT | (1<<8))
#define SQLITE_READONLY_RECOVERY (SQLITE_READONLY | (1<<8))
#define SQLITE_READONLY_CANTLOCK (SQLITE_READONLY | (2<<8))
In its default configuration, SQLite API routines return one of 26 integer
result codes
. However, experience has shown that many of
these result codes are too coarse-grained. They do not provide as
much information about problems as programmers might like. In an effort to
address this, newer versions of SQLite (version 3.3.8 and later) include
support for additional result codes that provide more detailed information
about errors. The extended result codes are enabled or disabled
on a per database connection basis using the
sqlite3_extended_result_codes()
API.
Some of the available extended result codes are listed here.
One may expect the number of extended result codes will be expand
over time. Software that uses extended result codes should expect
to see new result codes in future releases of SQLite.
The SQLITE_OK result code will never be extended. It will always
be exactly zero.
Checkpoint operation parameters
#define SQLITE_CHECKPOINT_PASSIVE 0
#define SQLITE_CHECKPOINT_FULL 1
#define SQLITE_CHECKPOINT_RESTART 2
These constants can be used as the 3rd parameter to
sqlite3_wal_checkpoint_v2()
. See the sqlite3_wal_checkpoint_v2()
documentation for additional information about the meaning and use of
each of these values.
Configuration Options
#define SQLITE_CONFIG_SINGLETHREAD 1 /* nil */
#define SQLITE_CONFIG_MULTITHREAD 2 /* nil */
#define SQLITE_CONFIG_SERIALIZED 3 /* nil */
#define SQLITE_CONFIG_MALLOC 4 /* sqlite3_mem_methods* */
#define SQLITE_CONFIG_GETMALLOC 5 /* sqlite3_mem_methods* */
#define SQLITE_CONFIG_SCRATCH 6 /* void*, int sz, int N */
#define SQLITE_CONFIG_PAGECACHE 7 /* void*, int sz, int N */
#define SQLITE_CONFIG_HEAP 8 /* void*, int nByte, int min */
#define SQLITE_CONFIG_MEMSTATUS 9 /* boolean */
#define SQLITE_CONFIG_MUTEX 10 /* sqlite3_mutex_methods* */
#define SQLITE_CONFIG_GETMUTEX 11 /* sqlite3_mutex_methods* */
/* previously SQLITE_CONFIG_CHUNKALLOC 12 which is now unused. */
#define SQLITE_CONFIG_LOOKASIDE 13 /* int int */
#define SQLITE_CONFIG_PCACHE 14 /* no-op */
#define SQLITE_CONFIG_GETPCACHE 15 /* no-op */
#define SQLITE_CONFIG_LOG 16 /* xFunc, void* */
#define SQLITE_CONFIG_URI 17 /* int */
#define SQLITE_CONFIG_PCACHE2 18 /* sqlite3_pcache_methods2* */
#define SQLITE_CONFIG_GETPCACHE2 19 /* sqlite3_pcache_methods2* */
These constants are the available integer configuration options that
can be passed as the first argument to the sqlite3_config()
interface.
New configuration options may be added in future releases of SQLite.
Existing configuration options might be discontinued. Applications
should check the return code from sqlite3_config()
to make sure that
the call worked. The sqlite3_config()
interface will return a
non-zero error code
if a discontinued or unsupported configuration option
is invoked.
SQLITE_CONFIG_SINGLETHREAD
There are no arguments to this option. This option sets the
threading mode
to Single-thread. In other words, it disables
all mutexing and puts SQLite into a mode where it can only be used
by a single thread. If SQLite is compiled with
the SQLITE_THREADSAFE=0
compile-time option then
it is not possible to change the threading mode
from its default
value of Single-thread and so sqlite3_config()
will return
SQLITE_ERROR
if called with the SQLITE_CONFIG_SINGLETHREAD
configuration option.
SQLITE_CONFIG_MULTITHREAD
There are no arguments to this option. This option sets the
threading mode
to Multi-thread. In other words, it disables
mutexing on database connection
and prepared statement
objects.
The application is responsible for serializing access to
database connections
and prepared statements
. But other mutexes
are enabled so that SQLite will be safe to use in a multi-threaded
environment as long as no two threads attempt to use the same
database connection
at the same time. If SQLite is compiled with
the SQLITE_THREADSAFE=0
compile-time option then
it is not possible to set the Multi-thread threading mode
and
sqlite3_config()
will return SQLITE_ERROR
if called with the
SQLITE_CONFIG_MULTITHREAD configuration option.
SQLITE_CONFIG_SERIALIZED
There are no arguments to this option. This option sets the
threading mode
to Serialized. In other words, this option enables
all mutexes including the recursive
mutexes on database connection
and prepared statement
objects.
In this mode (which is the default when SQLite is compiled with
SQLITE_THREADSAFE=1
) the SQLite library will itself serialize access
to database connections
and prepared statements
so that the
application is free to use the same database connection
or the
same prepared statement
in different threads at the same time.
If SQLite is compiled with
the SQLITE_THREADSAFE=0
compile-time option then
it is not possible to set the Serialized threading mode
and
sqlite3_config()
will return SQLITE_ERROR
if called with the
SQLITE_CONFIG_SERIALIZED configuration option.
SQLITE_CONFIG_MALLOC
This option takes a single argument which is a pointer to an
instance of the sqlite3_mem_methods
structure. The argument specifies
alternative low-level memory allocation routines to be used in place of
the memory allocation routines built into SQLite. SQLite makes
its own private copy of the content of the sqlite3_mem_methods
structure
before the sqlite3_config()
call returns.
SQLITE_CONFIG_GETMALLOC
This option takes a single argument which is a pointer to an
instance of the sqlite3_mem_methods
structure. The sqlite3_mem_methods
structure is filled with the currently defined memory allocation routines.
This option can be used to overload the default memory allocation
routines with a wrapper that simulations memory allocation failure or
tracks memory usage, for example.
SQLITE_CONFIG_MEMSTATUS
This option takes single argument of type int, interpreted as a
boolean, which enables or disables the collection of memory allocation
statistics. When memory allocation statistics are disabled, the
following SQLite interfaces become non-operational:
- sqlite3_memory_used()
- sqlite3_memory_highwater()
- sqlite3_soft_heap_limit64()
- sqlite3_status()
Memory allocation statistics are enabled by default unless SQLite is
compiled with SQLITE_DEFAULT_MEMSTATUS
=0 in which case memory
allocation statistics are disabled by default.
SQLITE_CONFIG_SCRATCH
This option specifies a static memory buffer that SQLite can use for
scratch memory. There are three arguments: A pointer an 8-byte
aligned memory buffer from which the scratch allocations will be
drawn, the size of each scratch allocation (sz),
and the maximum number of scratch allocations (N). The sz
argument must be a multiple of 16.
The first argument must be a pointer to an 8-byte aligned buffer
of at least sz*N bytes of memory.
SQLite will use no more than two scratch buffers per thread. So
N should be set to twice the expected maximum number of threads.
SQLite will never require a scratch buffer that is more than 6
times the database page size. If SQLite needs needs additional
scratch memory beyond what is provided by this configuration option, then
sqlite3_malloc()
will be used to obtain the memory needed.
SQLITE_CONFIG_PAGECACHE
This option specifies a static memory buffer that SQLite can use for
the database page cache with the default page cache implementation.
This configuration should not be used if an application-define page
cache implementation is loaded using the SQLITE_CONFIG_PCACHE2 option.
There are three arguments to this option: A pointer to 8-byte aligned
memory, the size of each page buffer (sz), and the number of pages (N).
The sz argument should be the size of the largest database page
(a power of two between 512 and 32768) plus a little extra for each
page header. The page header size is 20 to 40 bytes depending on
the host architecture. It is harmless, apart from the wasted memory,
to make sz a little too large. The first
argument should point to an allocation of at least sz*N bytes of memory.
SQLite will use the memory provided by the first argument to satisfy its
memory needs for the first N pages that it adds to cache. If additional
page cache memory is needed beyond what is provided by this option, then
SQLite goes to sqlite3_malloc()
for the additional storage space.
The pointer in the first argument must
be aligned to an 8-byte boundary or subsequent behavior of SQLite
will be undefined.
SQLITE_CONFIG_HEAP
This option specifies a static memory buffer that SQLite will use
for all of its dynamic memory allocation needs beyond those provided
for by SQLITE_CONFIG_SCRATCH
and SQLITE_CONFIG_PAGECACHE
.
There are three arguments: An 8-byte aligned pointer to the memory,
the number of bytes in the memory buffer, and the minimum allocation size.
If the first pointer (the memory pointer) is NULL, then SQLite reverts
to using its default memory allocator (the system malloc() implementation),
undoing any prior invocation of SQLITE_CONFIG_MALLOC
. If the
memory pointer is not NULL and either SQLITE_ENABLE_MEMSYS3
or
SQLITE_ENABLE_MEMSYS5
are defined, then the alternative memory
allocator is engaged to handle all of SQLites memory allocation needs.
The first pointer (the memory pointer) must be aligned to an 8-byte
boundary or subsequent behavior of SQLite will be undefined.
The minimum allocation size is capped at 2**12. Reasonable values
for the minimum allocation size are 2**5 through 2**8.
SQLITE_CONFIG_MUTEX
This option takes a single argument which is a pointer to an
instance of the sqlite3_mutex_methods
structure. The argument specifies
alternative low-level mutex routines to be used in place
the mutex routines built into SQLite. SQLite makes a copy of the
content of the sqlite3_mutex_methods
structure before the call to
sqlite3_config()
returns. If SQLite is compiled with
the SQLITE_THREADSAFE=0
compile-time option then
the entire mutexing subsystem is omitted from the build and hence calls to
sqlite3_config()
with the SQLITE_CONFIG_MUTEX configuration option will
return SQLITE_ERROR
.
SQLITE_CONFIG_GETMUTEX
This option takes a single argument which is a pointer to an
instance of the sqlite3_mutex_methods
structure. The
sqlite3_mutex_methods
structure is filled with the currently defined mutex routines.
This option can be used to overload the default mutex allocation
routines with a wrapper used to track mutex usage for performance
profiling or testing, for example. If SQLite is compiled with
the SQLITE_THREADSAFE=0
compile-time option then
the entire mutexing subsystem is omitted from the build and hence calls to
sqlite3_config()
with the SQLITE_CONFIG_GETMUTEX configuration option will
return SQLITE_ERROR
.
SQLITE_CONFIG_LOOKASIDE
This option takes two arguments that determine the default
memory allocation for the lookaside memory allocator on each
database connection
. The first argument is the
size of each lookaside buffer slot and the second is the number of
slots allocated to each database connection. This option sets the
default
lookaside size. The SQLITE_DBCONFIG_LOOKASIDE
verb to sqlite3_db_config()
can be used to change the lookaside
configuration on individual connections.
SQLITE_CONFIG_PCACHE2
This option takes a single argument which is a pointer to
an sqlite3_pcache_methods2
object. This object specifies the interface
to a custom page cache implementation. SQLite makes a copy of the
object and uses it for page cache memory allocations.
SQLITE_CONFIG_GETPCACHE2
This option takes a single argument which is a pointer to an
sqlite3_pcache_methods2
object. SQLite copies of the current
page cache implementation into that object.
SQLITE_CONFIG_LOG
The SQLITE_CONFIG_LOG option takes two arguments: a pointer to a
function with a call signature of void(*)(void*,int,const char*),
and a pointer to void. If the function pointer is not NULL, it is
invoked by sqlite3_log()
to process each logging event. If the
function pointer is NULL, the sqlite3_log()
interface becomes a no-op.
The void pointer that is the second argument to SQLITE_CONFIG_LOG is
passed through as the first parameter to the application-defined logger
function whenever that function is invoked. The second parameter to
the logger function is a copy of the first parameter to the corresponding
sqlite3_log()
call and is intended to be a result code
or an
extended result code
. The third parameter passed to the logger is
log message after formatting via sqlite3_snprintf()
.
The SQLite logging interface is not reentrant; the logger function
supplied by the application must not invoke any SQLite interface.
In a multi-threaded application, the application-defined logger
function must be threadsafe.
SQLITE_CONFIG_URI
This option takes a single argument of type int. If non-zero, then
URI handling is globally enabled. If the parameter is zero, then URI handling
is globally disabled. If URI handling is globally enabled, all filenames
passed to sqlite3_open()
, sqlite3_open_v2()
, sqlite3_open16()
or
specified as part of ATTACH
commands are interpreted as URIs, regardless
of whether or not the SQLITE_OPEN_URI
flag is set when the database
connection is opened. If it is globally disabled, filenames are
only interpreted as URIs if the SQLITE_OPEN_URI flag is set when the
database connection is opened. By default, URI handling is globally
disabled. The default value may be changed by compiling with the
SQLITE_USE_URI
symbol defined.
SQLITE_CONFIG_PCACHE and SQLITE_CONFNIG_GETPCACHE
These options are obsolete and should not be used by new code.
They are retained for backwards compatibility but are now no-ops.
Database Connection Configuration Options
#define SQLITE_DBCONFIG_LOOKASIDE 1001 /* void* int int */
#define SQLITE_DBCONFIG_ENABLE_FKEY 1002 /* int int* */
#define SQLITE_DBCONFIG_ENABLE_TRIGGER 1003 /* int int* */
These constants are the available integer configuration options that
can be passed as the second argument to the sqlite3_db_config()
interface.
New configuration options may be added in future releases of SQLite.
Existing configuration options might be discontinued. Applications
should check the return code from sqlite3_db_config()
to make sure that
the call worked. The sqlite3_db_config()
interface will return a
non-zero error code
if a discontinued or unsupported configuration option
is invoked.
SQLITE_DBCONFIG_LOOKASIDE
This option takes three additional arguments that determine the
lookaside memory allocator
configuration for the database connection
.
The first argument (the third parameter to sqlite3_db_config()
is a
pointer to a memory buffer to use for lookaside memory.
The first argument after the SQLITE_DBCONFIG_LOOKASIDE verb
may be NULL in which case SQLite will allocate the
lookaside buffer itself using sqlite3_malloc()
. The second argument is the
size of each lookaside buffer slot. The third argument is the number of
slots. The size of the buffer in the first argument must be greater than
or equal to the product of the second and third arguments. The buffer
must be aligned to an 8-byte boundary. If the second argument to
SQLITE_DBCONFIG_LOOKASIDE is not a multiple of 8, it is internally
rounded down to the next smaller multiple of 8. The lookaside memory
configuration for a database connection can only be changed when that
connection is not currently using lookaside memory, or in other words
when the "current value" returned by
sqlite3_db_status
(D,SQLITE_CONFIG_LOOKASIDE
,...) is zero.
Any attempt to change the lookaside memory configuration when lookaside
memory is in use leaves the configuration unchanged and returns
SQLITE_BUSY
.
SQLITE_DBCONFIG_ENABLE_FKEY
This option is used to enable or disable the enforcement of
foreign key constraints
. There should be two additional arguments.
The first argument is an integer which is 0 to disable FK enforcement,
positive to enable FK enforcement or negative to leave FK enforcement
unchanged. The second parameter is a pointer to an integer into which
is written 0 or 1 to indicate whether FK enforcement is off or on
following this call. The second parameter may be a NULL pointer, in
which case the FK enforcement setting is not reported back.
SQLITE_DBCONFIG_ENABLE_TRIGGER
This option is used to enable or disable triggers
.
There should be two additional arguments.
The first argument is an integer which is 0 to disable triggers,
positive to enable triggers or negative to leave the setting unchanged.
The second parameter is a pointer to an integer into which
is written 0 or 1 to indicate whether triggers are disabled or enabled
following this call. The second parameter may be a NULL pointer, in
which case the trigger setting is not reported back.
Authorizer Return Codes
#define SQLITE_DENY 1 /* Abort the SQL statement with an error */
#define SQLITE_IGNORE 2 /* Don't allow access, but don't generate an error */
The authorizer callback function
must
return either SQLITE_OK
or one of these two constants in order
to signal SQLite whether or not the action is permitted. See the
authorizer documentation
for additional
information.
Note that SQLITE_IGNORE is also used as a return code
from the sqlite3_vtab_on_conflict()
interface.
Conflict resolution modes
#define SQLITE_ROLLBACK 1
/* #define SQLITE_IGNORE 2 // Also used by sqlite3_authorizer() callback */
#define SQLITE_FAIL 3
/* #define SQLITE_ABORT 4 // Also an error code */
#define SQLITE_REPLACE 5
These constants are returned by sqlite3_vtab_on_conflict()
to
inform a virtual table
implementation what the ON CONFLICT
mode
is for the SQL statement being evaluated.
Note that the SQLITE_IGNORE
constant is also used as a potential
return value from the sqlite3_set_authorizer()
callback and that
SQLITE_ABORT
is also a result code
.
Standard File Control Opcodes
#define SQLITE_FCNTL_LOCKSTATE 1
#define SQLITE_GET_LOCKPROXYFILE 2
#define SQLITE_SET_LOCKPROXYFILE 3
#define SQLITE_LAST_ERRNO 4
#define SQLITE_FCNTL_SIZE_HINT 5
#define SQLITE_FCNTL_CHUNK_SIZE 6
#define SQLITE_FCNTL_FILE_POINTER 7
#define SQLITE_FCNTL_SYNC_OMITTED 8
#define SQLITE_FCNTL_WIN32_AV_RETRY 9
#define SQLITE_FCNTL_PERSIST_WAL 10
#define SQLITE_FCNTL_OVERWRITE 11
#define SQLITE_FCNTL_VFSNAME 12
#define SQLITE_FCNTL_POWERSAFE_OVERWRITE 13
These integer constants are opcodes for the xFileControl method
of the sqlite3_io_methods
object and for the sqlite3_file_control()
interface.
The SQLITE_FCNTL_LOCKSTATE
opcode is used for debugging. This
opcode causes the xFileControl method to write the current state of
the lock (one of SQLITE_LOCK_NONE
, SQLITE_LOCK_SHARED
,
SQLITE_LOCK_RESERVED
, SQLITE_LOCK_PENDING
, or SQLITE_LOCK_EXCLUSIVE
)
into an integer that the pArg argument points to. This capability
is used during testing and only needs to be supported when SQLITE_TEST
is defined.
The SQLITE_FCNTL_SIZE_HINT
opcode is used by SQLite to give the VFS
layer a hint of how large the database file will grow to be during the
current transaction. This hint is not guaranteed to be accurate but it
is often close. The underlying VFS might choose to preallocate database
file space based on this hint in order to help writes to the database
file run faster.
The SQLITE_FCNTL_CHUNK_SIZE
opcode is used to request that the VFS
extends and truncates the database file in chunks of a size specified
by the user. The fourth argument to sqlite3_file_control()
should
point to an integer (type int) containing the new chunk-size to use
for the nominated database. Allocating database file space in large
chunks (say 1MB at a time), may reduce file-system fragmentation and
improve performance on some systems.
The SQLITE_FCNTL_FILE_POINTER
opcode is used to obtain a pointer
to the sqlite3_file
object associated with a particular database
connection. See the sqlite3_file_control()
documentation for
additional information.
The SQLITE_FCNTL_SYNC_OMITTED
opcode is generated internally by
SQLite and sent to all VFSes in place of a call to the xSync method
when the database connection has PRAGMA synchronous
set to OFF.
Some specialized VFSes need this signal in order to operate correctly
when PRAGMA synchronous=OFF
is set, but most
VFSes do not need this signal and should silently ignore this opcode.
Applications should not call sqlite3_file_control()
with this
opcode as doing so may disrupt the operation of the specialized VFSes
that do require it.
The SQLITE_FCNTL_WIN32_AV_RETRY
opcode is used to configure automatic
retry counts and intervals for certain disk I/O operations for the
windows VFS
in order to provide robustness in the presence of
anti-virus programs. By default, the windows VFS will retry file read,
file write, and file delete operations up to 10 times, with a delay
of 25 milliseconds before the first retry and with the delay increasing
by an additional 25 milliseconds with each subsequent retry. This
opcode allows these two values (10 retries and 25 milliseconds of delay)
to be adjusted. The values are changed for all database connections
within the same process. The argument is a pointer to an array of two
integers where the first integer i the new retry count and the second
integer is the delay. If either integer is negative, then the setting
is not changed but instead the prior value of that setting is written
into the array entry, allowing the current retry settings to be
interrogated. The zDbName parameter is ignored.
The SQLITE_FCNTL_PERSIST_WAL
opcode is used to set or query the
persistent Write AHead Log
setting. By default, the auxiliary
write ahead log and shared memory files used for transaction control
are automatically deleted when the latest connection to the database
closes. Setting persistent WAL mode causes those files to persist after
close. Persisting the files is useful when other processes that do not
have write permission on the directory containing the database file want
to read the database file, as the WAL and shared memory files must exist
in order for the database to be readable. The fourth parameter to
sqlite3_file_control()
for this opcode should be a pointer to an integer.
That integer is 0 to disable persistent WAL mode or 1 to enable persistent
WAL mode. If the integer is -1, then it is overwritten with the current
WAL persistence setting.
The SQLITE_FCNTL_POWERSAFE_OVERWRITE
opcode is used to set or query the
persistent "powersafe-overwrite" or "PSOW" setting. The PSOW setting
determines the SQLITE_IOCAP_POWERSAFE_OVERWRITE
bit of the
xDeviceCharacteristics methods. The fourth parameter to
sqlite3_file_control()
for this opcode should be a pointer to an integer.
That integer is 0 to disable zero-damage mode or 1 to enable zero-damage
mode. If the integer is -1, then it is overwritten with the current
zero-damage mode setting.
The SQLITE_FCNTL_OVERWRITE
opcode is invoked by SQLite after opening
a write transaction to indicate that, unless it is rolled back for some
reason, the entire database file will be overwritten by the current
transaction. This is used by VACUUM operations.
The SQLITE_FCNTL_VFSNAME
opcode can be used to obtain the names of
all VFSes
in the VFS stack. The names are of all VFS shims and the
final bottom-level VFS are written into memory obtained from
sqlite3_malloc()
and the result is stored in the char* variable
that the fourth parameter of sqlite3_file_control()
points to.
The caller is responsible for freeing the memory when done. As with
all file-control actions, there is no guarantee that this will actually
do anything. Callers should initialize the char* variable to a NULL
pointer in case this file-control is not implemented. This file-control
is intended for diagnostic use only.
Virtual Table Constraint Operator Codes
#define SQLITE_INDEX_CONSTRAINT_EQ 2
#define SQLITE_INDEX_CONSTRAINT_GT 4
#define SQLITE_INDEX_CONSTRAINT_LE 8
#define SQLITE_INDEX_CONSTRAINT_LT 16
#define SQLITE_INDEX_CONSTRAINT_GE 32
#define SQLITE_INDEX_CONSTRAINT_MATCH 64
These macros defined the allowed values for the
sqlite3_index_info
.aConstraint[].op field. Each value represents
an operator that is part of a constraint term in the wHERE clause of
a query that uses a virtual table
.
Device Characteristics
#define SQLITE_IOCAP_ATOMIC 0x00000001
#define SQLITE_IOCAP_ATOMIC512 0x00000002
#define SQLITE_IOCAP_ATOMIC1K 0x00000004
#define SQLITE_IOCAP_ATOMIC2K 0x00000008
#define SQLITE_IOCAP_ATOMIC4K 0x00000010
#define SQLITE_IOCAP_ATOMIC8K 0x00000020
#define SQLITE_IOCAP_ATOMIC16K 0x00000040
#define SQLITE_IOCAP_ATOMIC32K 0x00000080
#define SQLITE_IOCAP_ATOMIC64K 0x00000100
#define SQLITE_IOCAP_SAFE_APPEND 0x00000200
#define SQLITE_IOCAP_SEQUENTIAL 0x00000400
#define SQLITE_IOCAP_UNDELETABLE_WHEN_OPEN 0x00000800
#define SQLITE_IOCAP_POWERSAFE_OVERWRITE 0x00001000
The xDeviceCharacteristics method of the sqlite3_io_methods
object returns an integer which is a vector of the these
bit values expressing I/O characteristics of the mass storage
device that holds the file that the sqlite3_io_methods
refers to.
The SQLITE_IOCAP_ATOMIC property means that all writes of
any size are atomic. The SQLITE_IOCAP_ATOMICnnn values
mean that writes of blocks that are nnn bytes in size and
are aligned to an address which is an integer multiple of
nnn are atomic. The SQLITE_IOCAP_SAFE_APPEND value means
that when data is appended to a file, the data is appended
first then the size of the file is extended, never the other
way around. The SQLITE_IOCAP_SEQUENTIAL property means that
information is written to disk in the same order as calls
to xWrite(). The SQLITE_IOCAP_POWERSAFE_OVERWRITE property means that
after reboot following a crash or power loss, the only bytes in a
file that were written at the application level might have changed
and that adjacent bytes, even bytes within the same sector are
guaranteed to be unchanged.
File Locking Levels
#define SQLITE_LOCK_NONE 0
#define SQLITE_LOCK_SHARED 1
#define SQLITE_LOCK_RESERVED 2
#define SQLITE_LOCK_PENDING 3
#define SQLITE_LOCK_EXCLUSIVE 4
SQLite uses one of these integer values as the second
argument to calls it makes to the xLock() and xUnlock() methods
of an sqlite3_io_methods
object.
Mutex Types
#define SQLITE_MUTEX_FAST 0
#define SQLITE_MUTEX_RECURSIVE 1
#define SQLITE_MUTEX_STATIC_MASTER 2
#define SQLITE_MUTEX_STATIC_MEM 3 /* sqlite3_malloc() */
#define SQLITE_MUTEX_STATIC_MEM2 4 /* NOT USED */
#define SQLITE_MUTEX_STATIC_OPEN 4 /* sqlite3BtreeOpen() */
#define SQLITE_MUTEX_STATIC_PRNG 5 /* sqlite3_random() */
#define SQLITE_MUTEX_STATIC_LRU 6 /* lru page list */
#define SQLITE_MUTEX_STATIC_LRU2 7 /* NOT USED */
#define SQLITE_MUTEX_STATIC_PMEM 7 /* sqlite3PageMalloc() */
The sqlite3_mutex_alloc()
interface takes a single argument
which is one of these integer constants.
The set of static mutexes may change from one SQLite release to the
next. Applications that override the built-in mutex logic must be
prepared to accommodate additional static mutexes.
Flags For File Open Operations
#define SQLITE_OPEN_READONLY 0x00000001 /* Ok for sqlite3_open_v2() */
#define SQLITE_OPEN_READWRITE 0x00000002 /* Ok for sqlite3_open_v2() */
#define SQLITE_OPEN_CREATE 0x00000004 /* Ok for sqlite3_open_v2() */
#define SQLITE_OPEN_DELETEONCLOSE 0x00000008 /* VFS only */
#define SQLITE_OPEN_EXCLUSIVE 0x00000010 /* VFS only */
#define SQLITE_OPEN_AUTOPROXY 0x00000020 /* VFS only */
#define SQLITE_OPEN_URI 0x00000040 /* Ok for sqlite3_open_v2() */
#define SQLITE_OPEN_MAIN_DB 0x00000100 /* VFS only */
#define SQLITE_OPEN_TEMP_DB 0x00000200 /* VFS only */
#define SQLITE_OPEN_TRANSIENT_DB 0x00000400 /* VFS only */
#define SQLITE_OPEN_MAIN_JOURNAL 0x00000800 /* VFS only */
#define SQLITE_OPEN_TEMP_JOURNAL 0x00001000 /* VFS only */
#define SQLITE_OPEN_SUBJOURNAL 0x00002000 /* VFS only */
#define SQLITE_OPEN_MASTER_JOURNAL 0x00004000 /* VFS only */
#define SQLITE_OPEN_NOMUTEX 0x00008000 /* Ok for sqlite3_open_v2() */
#define SQLITE_OPEN_FULLMUTEX 0x00010000 /* Ok for sqlite3_open_v2() */
#define SQLITE_OPEN_SHAREDCACHE 0x00020000 /* Ok for sqlite3_open_v2() */
#define SQLITE_OPEN_PRIVATECACHE 0x00040000 /* Ok for sqlite3_open_v2() */
#define SQLITE_OPEN_WAL 0x00080000 /* VFS only */
These bit values are intended for use in the
3rd parameter to the sqlite3_open_v2()
interface and
in the 4th parameter to the sqlite3_vfs.xOpen
method.
Flags for the xShmLock VFS method
#define SQLITE_SHM_UNLOCK 1
#define SQLITE_SHM_LOCK 2
#define SQLITE_SHM_SHARED 4
#define SQLITE_SHM_EXCLUSIVE 8
These integer constants define the various locking operations
allowed by the xShmLock method of sqlite3_io_methods
. The
following are the only legal combinations of flags to the
xShmLock method:
- SQLITE_SHM_LOCK | SQLITE_SHM_SHARED
- SQLITE_SHM_LOCK | SQLITE_SHM_EXCLUSIVE
- SQLITE_SHM_UNLOCK | SQLITE_SHM_SHARED
- SQLITE_SHM_UNLOCK | SQLITE_SHM_EXCLUSIVE
When unlocking, the same SHARED or EXCLUSIVE flag must be supplied as
was given no the corresponding lock.
The xShmLock method can transition between unlocked and SHARED or
between unlocked and EXCLUSIVE. It cannot transition between SHARED
and EXCLUSIVE.
Compile-Time Library Version Numbers
#define SQLITE_VERSION "3.7.10"
#define SQLITE_VERSION_NUMBER 3007010
#define SQLITE_SOURCE_ID "2012-01-16 16:56:31 93aa17d866873e11dde5ffbefe74497f229977c1"
The SQLITE_VERSION
C preprocessor macro in the sqlite3.h header
evaluates to a string literal that is the SQLite version in the
format "X.Y.Z" where X is the major version number (always 3 for
SQLite3) and Y is the minor version number and Z is the release number.
The SQLITE_VERSION_NUMBER
C preprocessor macro resolves to an integer
with the value (X*1000000 + Y*1000 + Z) where X, Y, and Z are the same
numbers used in SQLITE_VERSION
.
The SQLITE_VERSION_NUMBER for any given release of SQLite will also
be larger than the release from which it is derived. Either Y will
be held constant and Z will be incremented or else Y will be incremented
and Z will be reset to zero.
Since version 3.6.18, SQLite source code has been stored in the
Fossil configuration management
system
. The SQLITE_SOURCE_ID macro evaluates to
a string which identifies a particular check-in of SQLite
within its configuration management system. The SQLITE_SOURCE_ID
string contains the date and time of the check-in (UTC) and an SHA1
hash of the entire source tree.
See also: sqlite3_libversion()
,
sqlite3_libversion_number()
, sqlite3_sourceid()
,
sqlite_version()
and sqlite_source_id()
.
Constants Defining Special Destructor Behavior
typedef void (*sqlite3_destructor_type)(void*);
#define SQLITE_STATIC ((sqlite3_destructor_type)0)
#define SQLITE_TRANSIENT ((sqlite3_destructor_type)-1)
These are special values for the destructor that is passed in as the
final argument to routines like sqlite3_result_blob()
. If the destructor
argument is SQLITE_STATIC, it means that the content pointer is constant
and will never change. It does not need to be destroyed. The
SQLITE_TRANSIENT value means that the content will likely change in
the near future and that SQLite should make its own private copy of
the content before returning.
The typedef is necessary to work around problems in certain
C++ compilers. See ticket #2191.
Status Parameters
#define SQLITE_STATUS_MEMORY_USED 0
#define SQLITE_STATUS_PAGECACHE_USED 1
#define SQLITE_STATUS_PAGECACHE_OVERFLOW 2
#define SQLITE_STATUS_SCRATCH_USED 3
#define SQLITE_STATUS_SCRATCH_OVERFLOW 4
#define SQLITE_STATUS_MALLOC_SIZE 5
#define SQLITE_STATUS_PARSER_STACK 6
#define SQLITE_STATUS_PAGECACHE_SIZE 7
#define SQLITE_STATUS_SCRATCH_SIZE 8
#define SQLITE_STATUS_MALLOC_COUNT 9
These integer constants designate various run-time status parameters
that can be returned by sqlite3_status()
.
SQLITE_STATUS_MEMORY_USED
This parameter is the current amount of memory checked out
using sqlite3_malloc()
, either directly or indirectly. The
figure includes calls made to sqlite3_malloc()
by the application
and internal memory usage by the SQLite library. Scratch memory
controlled by SQLITE_CONFIG_SCRATCH
and auxiliary page-cache
memory controlled by SQLITE_CONFIG_PAGECACHE
is not included in
this parameter. The amount returned is the sum of the allocation
sizes as reported by the xSize method in sqlite3_mem_methods
.
SQLITE_STATUS_MALLOC_SIZE
This parameter records the largest memory allocation request
handed to sqlite3_malloc()
or sqlite3_realloc()
(or their
internal equivalents). Only the value returned in the
*pHighwater parameter to sqlite3_status()
is of interest.
The value written into the *pCurrent parameter is undefined.
SQLITE_STATUS_MALLOC_COUNT
This parameter records the number of separate memory allocations
currently checked out.
SQLITE_STATUS_PAGECACHE_USED
This parameter returns the number of pages used out of the
pagecache memory allocator
that was configured using
SQLITE_CONFIG_PAGECACHE
. The
value returned is in pages, not in bytes.
SQLITE_STATUS_PAGECACHE_OVERFLOW
This parameter returns the number of bytes of page cache
allocation which could not be satisfied by the SQLITE_CONFIG_PAGECACHE
buffer and where forced to overflow to sqlite3_malloc()
. The
returned value includes allocations that overflowed because they
where too large (they were larger than the "sz" parameter to
SQLITE_CONFIG_PAGECACHE
) and allocations that overflowed because
no space was left in the page cache.
SQLITE_STATUS_PAGECACHE_SIZE
This parameter records the largest memory allocation request
handed to pagecache memory allocator
. Only the value returned in the
*pHighwater parameter to sqlite3_status()
is of interest.
The value written into the *pCurrent parameter is undefined.
SQLITE_STATUS_SCRATCH_USED
This parameter returns the number of allocations used out of the
scratch memory allocator
configured using
SQLITE_CONFIG_SCRATCH
. The value returned is in allocations, not
in bytes. Since a single thread may only have one scratch allocation
outstanding at time, this parameter also reports the number of threads
using scratch memory at the same time.
SQLITE_STATUS_SCRATCH_OVERFLOW
This parameter returns the number of bytes of scratch memory
allocation which could not be satisfied by the SQLITE_CONFIG_SCRATCH
buffer and where forced to overflow to sqlite3_malloc()
. The values
returned include overflows because the requested allocation was too
larger (that is, because the requested allocation was larger than the
"sz" parameter to SQLITE_CONFIG_SCRATCH
) and because no scratch buffer
slots were available.
SQLITE_STATUS_SCRATCH_SIZE
This parameter records the largest memory allocation request
handed to scratch memory allocator
. Only the value returned in the
*pHighwater parameter to sqlite3_status()
is of interest.
The value written into the *pCurrent parameter is undefined.
SQLITE_STATUS_PARSER_STACK
This parameter records the deepest parser stack. It is only
meaningful if SQLite is compiled with YYTRACKMAXSTACKDEPTH
. New status parameters may be added from time to time.
Synchronization Type Flags
#define SQLITE_SYNC_NORMAL 0x00002
#define SQLITE_SYNC_FULL 0x00003
#define SQLITE_SYNC_DATAONLY 0x00010
When SQLite invokes the xSync() method of an
sqlite3_io_methods
object it uses a combination of
these integer values as the second argument.
When the SQLITE_SYNC_DATAONLY flag is used, it means that the
sync operation only needs to flush data to mass storage. Inode
information need not be flushed. If the lower four bits of the flag
equal SQLITE_SYNC_NORMAL, that means to use normal fsync() semantics.
If the lower four bits equal SQLITE_SYNC_FULL, that means
to use Mac OS X style fullsync instead of fsync().
Do not confuse the SQLITE_SYNC_NORMAL and SQLITE_SYNC_FULL flags
with the PRAGMA synchronous
=NORMAL and PRAGMA synchronous
=FULL
settings. The synchronous pragma
determines when calls to the
xSync VFS method occur and applies uniformly across all platforms.
The SQLITE_SYNC_NORMAL and SQLITE_SYNC_FULL flags determine how
energetic or rigorous or forceful the sync operations are and
only make a difference on Mac OSX for the default SQLite code.
(Third-party VFS implementations might also make the distinction
between SQLITE_SYNC_NORMAL and SQLITE_SYNC_FULL, but among the
operating systems natively supported by SQLite, only Mac OSX
cares about the difference.)
Testing Interface Operation Codes
#define SQLITE_TESTCTRL_FIRST 5
#define SQLITE_TESTCTRL_PRNG_SAVE 5
#define SQLITE_TESTCTRL_PRNG_RESTORE 6
#define SQLITE_TESTCTRL_PRNG_RESET 7
#define SQLITE_TESTCTRL_BITVEC_TEST 8
#define SQLITE_TESTCTRL_FAULT_INSTALL 9
#define SQLITE_TESTCTRL_BENIGN_MALLOC_HOOKS 10
#define SQLITE_TESTCTRL_PENDING_BYTE 11
#define SQLITE_TESTCTRL_ASSERT 12
#define SQLITE_TESTCTRL_ALWAYS 13
#define SQLITE_TESTCTRL_RESERVE 14
#define SQLITE_TESTCTRL_OPTIMIZATIONS 15
#define SQLITE_TESTCTRL_ISKEYWORD 16
#define SQLITE_TESTCTRL_SCRATCHMALLOC 17
#define SQLITE_TESTCTRL_LOCALTIME_FAULT 18
#define SQLITE_TESTCTRL_EXPLAIN_STMT 19
#define SQLITE_TESTCTRL_LAST 19
These constants are the valid operation code parameters used
as the first argument to sqlite3_test_control()
.
These parameters and their meanings are subject to change
without notice. These values are for testing purposes only.
Applications should not use any of these parameters or the
sqlite3_test_control()
interface.
Run-Time Limit Categories
#define SQLITE_LIMIT_LENGTH 0
#define SQLITE_LIMIT_SQL_LENGTH 1
#define SQLITE_LIMIT_COLUMN 2
#define SQLITE_LIMIT_EXPR_DEPTH 3
#define SQLITE_LIMIT_COMPOUND_SELECT 4
#define SQLITE_LIMIT_VDBE_OP 5
#define SQLITE_LIMIT_FUNCTION_ARG 6
#define SQLITE_LIMIT_ATTACHED 7
#define SQLITE_LIMIT_LIKE_PATTERN_LENGTH 8
#define SQLITE_LIMIT_VARIABLE_NUMBER 9
#define SQLITE_LIMIT_TRIGGER_DEPTH 10
These constants define various performance limits
that can be lowered at run-time using sqlite3_limit()
.
The synopsis of the meanings of the various limits is shown below.
Additional information is available at Limits in SQLite
.
SQLITE_LIMIT_LENGTH
The maximum size of any string or BLOB or table row, in bytes.
SQLITE_LIMIT_SQL_LENGTH
The maximum length of an SQL statement, in bytes.
SQLITE_LIMIT_COLUMN
The maximum number of columns in a table definition or in the
result set of a SELECT
or the maximum number of columns in an index
or in an ORDER BY or GROUP BY clause.
SQLITE_LIMIT_EXPR_DEPTH
The maximum depth of the parse tree on any expression.
SQLITE_LIMIT_COMPOUND_SELECT
The maximum number of terms in a compound SELECT statement.
SQLITE_LIMIT_VDBE_OP
The maximum number of instructions in a virtual machine program
used to implement an SQL statement. This limit is not currently
enforced, though that might be added in some future release of
SQLite.
SQLITE_LIMIT_FUNCTION_ARG
The maximum number of arguments on a function.
SQLITE_LIMIT_ATTACHED
The maximum number of attached databases
.
SQLITE_LIMIT_LIKE_PATTERN_LENGTH
The maximum length of the pattern argument to the LIKE
or
GLOB
operators.
SQLITE_LIMIT_VARIABLE_NUMBER
The maximum index number of any parameter
in an SQL statement.
SQLITE_LIMIT_TRIGGER_DEPTH
The maximum depth of recursion for triggers.
Status Parameters for database connections
#define SQLITE_DBSTATUS_LOOKASIDE_USED 0
#define SQLITE_DBSTATUS_CACHE_USED 1
#define SQLITE_DBSTATUS_SCHEMA_USED 2
#define SQLITE_DBSTATUS_STMT_USED 3
#define SQLITE_DBSTATUS_LOOKASIDE_HIT 4
#define SQLITE_DBSTATUS_LOOKASIDE_MISS_SIZE 5
#define SQLITE_DBSTATUS_LOOKASIDE_MISS_FULL 6
#define SQLITE_DBSTATUS_CACHE_HIT 7
#define SQLITE_DBSTATUS_CACHE_MISS 8
#define SQLITE_DBSTATUS_MAX 8 /* Largest defined DBSTATUS */
These constants are the available integer "verbs" that can be passed as
the second argument to the sqlite3_db_status()
interface.
New verbs may be added in future releases of SQLite. Existing verbs
might be discontinued. Applications should check the return code from
sqlite3_db_status()
to make sure that the call worked.
The sqlite3_db_status()
interface will return a non-zero error code
if a discontinued or unsupported verb is invoked.
SQLITE_DBSTATUS_LOOKASIDE_USED
This parameter returns the number of lookaside memory slots currently
checked out.
SQLITE_DBSTATUS_LOOKASIDE_HIT
This parameter returns the number malloc attempts that were
satisfied using lookaside memory. Only the high-water value is meaningful;
the current value is always zero.
SQLITE_DBSTATUS_LOOKASIDE_MISS_SIZE
This parameter returns the number malloc attempts that might have
been satisfied using lookaside memory but failed due to the amount of
memory requested being larger than the lookaside slot size.
Only the high-water value is meaningful;
the current value is always zero.
SQLITE_DBSTATUS_LOOKASIDE_MISS_FULL
This parameter returns the number malloc attempts that might have
been satisfied using lookaside memory but failed due to all lookaside
memory already being in use.
Only the high-water value is meaningful;
the current value is always zero.
SQLITE_DBSTATUS_CACHE_USED
This parameter returns the approximate number of of bytes of heap
memory used by all pager caches associated with the database connection.
The highwater mark associated with SQLITE_DBSTATUS_CACHE_USED is always 0.
SQLITE_DBSTATUS_SCHEMA_USED
This parameter returns the approximate number of of bytes of heap
memory used to store the schema for all databases associated
with the connection - main, temp, and any ATTACH
-ed databases.
The full amount of memory used by the schemas is reported, even if the
schema memory is shared with other database connections due to
shared cache mode
being enabled.
The highwater mark associated with SQLITE_DBSTATUS_SCHEMA_USED is always 0.
SQLITE_DBSTATUS_STMT_USED
This parameter returns the approximate number of of bytes of heap
and lookaside memory used by all prepared statements associated with
the database connection.
The highwater mark associated with SQLITE_DBSTATUS_STMT_USED is always 0.
SQLITE_DBSTATUS_CACHE_HIT
This parameter returns the number of pager cache hits that have
occurred. The highwater mark associated with SQLITE_DBSTATUS_CACHE_HIT
is always 0.
SQLITE_DBSTATUS_CACHE_MISS
This parameter returns the number of pager cache misses that have
occurred. The highwater mark associated with SQLITE_DBSTATUS_CACHE_MISS
is always 0.
Status Parameters for prepared statements
#define SQLITE_STMTSTATUS_FULLSCAN_STEP 1
#define SQLITE_STMTSTATUS_SORT 2
#define SQLITE_STMTSTATUS_AUTOINDEX 3
These preprocessor macros define integer codes that name counter
values associated with the sqlite3_stmt_status()
interface.
The meanings of the various counters are as follows:
SQLITE_STMTSTATUS_FULLSCAN_STEP
This is the number of times that SQLite has stepped forward in
a table as part of a full table scan. Large numbers for this counter
may indicate opportunities for performance improvement through
careful use of indices.
SQLITE_STMTSTATUS_SORT
This is the number of sort operations that have occurred.
A non-zero value in this counter may indicate an opportunity to
improvement performance through careful use of indices.
SQLITE_STMTSTATUS_AUTOINDEX
This is the number of rows inserted into transient indices that
were created automatically in order to help joins run faster.
A non-zero value in this counter may indicate an opportunity to
improvement performance by adding permanent indices that do not
need to be reinitialized each time the statement is run.
64-Bit Integer Types
#ifdef SQLITE_INT64_TYPE
typedef SQLITE_INT64_TYPE sqlite_int64;
typedef unsigned SQLITE_INT64_TYPE sqlite_uint64;
#elif defined(_MSC_VER) || defined(__BORLANDC__)
typedef __int64 sqlite_int64;
typedef unsigned __int64 sqlite_uint64;
#else
typedef long long int sqlite_int64;
typedef unsigned long long int sqlite_uint64;
#endif
typedef sqlite_int64 sqlite3_int64;
typedef sqlite_uint64 sqlite3_uint64;
Because there is no cross-platform way to specify 64-bit integer types
SQLite includes typedefs for 64-bit signed and unsigned integers.
The sqlite3_int64 and sqlite3_uint64 are the preferred type definitions.
The sqlite_int64 and sqlite_uint64 types are supported for backwards
compatibility only.
The sqlite3_int64 and sqlite_int64 types can store integer values
between -9223372036854775808 and +9223372036854775807 inclusive. The
sqlite3_uint64 and sqlite_uint64 types can store integer values
between 0 and +18446744073709551615 inclusive.
Virtual Table Object
struct sqlite3_module {
int iVersion;
int (*xCreate)(sqlite3*, void *pAux,
int argc, const char *const*argv,
sqlite3_vtab **ppVTab, char**);
int (*xConnect)(sqlite3*, void *pAux,
int argc, const char *const*argv,
sqlite3_vtab **ppVTab, char**);
int (*xBestIndex)(sqlite3_vtab *pVTab, sqlite3_index_info*);
int (*xDisconnect)(sqlite3_vtab *pVTab);
int (*xDestroy)(sqlite3_vtab *pVTab);
int (*xOpen)(sqlite3_vtab *pVTab, sqlite3_vtab_cursor **ppCursor);
int (*xClose)(sqlite3_vtab_cursor*);
int (*xFilter)(sqlite3_vtab_cursor*, int idxNum, const char *idxStr,
int argc, sqlite3_value **argv);
int (*xNext)(sqlite3_vtab_cursor*);
int (*xEof)(sqlite3_vtab_cursor*);
int (*xColumn)(sqlite3_vtab_cursor*, sqlite3_context*, int);
int (*xRowid)(sqlite3_vtab_cursor*, sqlite3_int64 *pRowid);
int (*xUpdate)(sqlite3_vtab *, int, sqlite3_value **, sqlite3_int64 *);
int (*xBegin)(sqlite3_vtab *pVTab);
int (*xSync)(sqlite3_vtab *pVTab);
int (*xCommit)(sqlite3_vtab *pVTab);
int (*xRollback)(sqlite3_vtab *pVTab);
int (*xFindFunction)(sqlite3_vtab *pVtab, int nArg, const char *zName,
void (**pxFunc)(sqlite3_context*,int,sqlite3_value**),
void **ppArg);
int (*xRename)(sqlite3_vtab *pVtab, const char *zNew);
/* The methods above are in version 1 of the sqlite_module object. Those
** below are for version 2 and greater. */
int (*xSavepoint)(sqlite3_vtab *pVTab, int);
int (*xRelease)(sqlite3_vtab *pVTab, int);
int (*xRollbackTo)(sqlite3_vtab *pVTab, int);
};
This structure, sometimes called a "virtual table module",
defines the implementation of a virtual tables
.
This structure consists mostly of methods for the module.
A virtual table module is created by filling in a persistent
instance of this structure and passing a pointer to that instance
to sqlite3_create_module()
or sqlite3_create_module_v2()
.
The registration remains valid until it is replaced by a different
module or until the database connection
closes. The content
of this structure must not change while it is registered with
any database connection.
Virtual Table Cursor Object
struct sqlite3_vtab_cursor {
sqlite3_vtab *pVtab; /* Virtual table of this cursor */
/* Virtual table implementations will typically add additional fields */
};
Every virtual table module
implementation uses a subclass of the
following structure to describe cursors that point into the
virtual table
and are used
to loop through the virtual table. Cursors are created using the
xOpen
method of the module and are destroyed
by the xClose
method. Cursors are used
by the xFilter
, xNext
, xEof
, xColumn
, and xRowid
methods
of the module. Each module implementation will define
the content of a cursor structure to suit its own needs.
This superclass exists in order to define fields of the cursor that
are common to all implementations.
A Handle To An Open BLOB
typedef struct sqlite3_blob sqlite3_blob;
An instance of this object represents an open BLOB on which
incremental BLOB I/O
can be performed.
Objects of this type are created by sqlite3_blob_open()
and destroyed by sqlite3_blob_close()
.
The sqlite3_blob_read()
and sqlite3_blob_write()
interfaces
can be used to read or write small subsections of the BLOB.
The sqlite3_blob_bytes()
interface returns the size of the BLOB in bytes.
Database Connection Handle
typedef struct sqlite3 sqlite3;
Each open SQLite database is represented by a pointer to an instance of
the opaque structure named "sqlite3". It is useful to think of an sqlite3
pointer as an object. The sqlite3_open()
, sqlite3_open16()
, and
sqlite3_open_v2()
interfaces are its constructors, and sqlite3_close()
is its destructor. There are many other interfaces (such as
sqlite3_prepare_v2()
, sqlite3_create_function()
, and
sqlite3_busy_timeout()
to name but three) that are methods on an
sqlite3 object.
Application Defined Page Cache.
typedef struct sqlite3_pcache_methods2 sqlite3_pcache_methods2;
struct sqlite3_pcache_methods2 {
int iVersion;
void *pArg;
int (*xInit)(void*);
void (*xShutdown)(void*);
sqlite3_pcache *(*xCreate)(int szPage, int szExtra, int bPurgeable);
void (*xCachesize)(sqlite3_pcache*, int nCachesize);
int (*xPagecount)(sqlite3_pcache*);
sqlite3_pcache_page *(*xFetch)(sqlite3_pcache*, unsigned key, int createFlag);
void (*xUnpin)(sqlite3_pcache*, sqlite3_pcache_page*, int discard);
void (*xRekey)(sqlite3_pcache*, sqlite3_pcache_page*,
unsigned oldKey, unsigned newKey);
void (*xTruncate)(sqlite3_pcache*, unsigned iLimit);
void (*xDestroy)(sqlite3_pcache*);
void (*xShrink)(sqlite3_pcache*);
};
The sqlite3_config
(SQLITE_CONFIG_PCACHE2
, ...) interface can
register an alternative page cache implementation by passing in an
instance of the sqlite3_pcache_methods2 structure.
In many applications, most of the heap memory allocated by
SQLite is used for the page cache.
By implementing a
custom page cache using this API, an application can better control
the amount of memory consumed by SQLite, the way in which
that memory is allocated and released, and the policies used to
determine exactly which parts of a database file are cached and for
how long.
The alternative page cache mechanism is an
extreme measure that is only needed by the most demanding applications.
The built-in page cache is recommended for most uses.
The contents of the sqlite3_pcache_methods2 structure are copied to an
internal buffer by SQLite within the call to sqlite3_config
. Hence
the application may discard the parameter after the call to
sqlite3_config()
returns.
The xInit() method is called once for each effective
call to sqlite3_initialize()
(usually only once during the lifetime of the process). The xInit()
method is passed a copy of the sqlite3_pcache_methods2.pArg value.
The intent of the xInit() method is to set up global data structures
required by the custom page cache implementation.
If the xInit() method is NULL, then the
built-in default page cache is used instead of the application defined
page cache.
The xShutdown() method is called by sqlite3_shutdown()
.
It can be used to clean up
any outstanding resources before process shutdown, if required.
The xShutdown() method may be NULL.
SQLite automatically serializes calls to the xInit method,
so the xInit method need not be threadsafe. The
xShutdown method is only called from sqlite3_shutdown()
so it does
not need to be threadsafe either. All other methods must be threadsafe
in multithreaded applications.
SQLite will never invoke xInit() more than once without an intervening
call to xShutdown().
SQLite invokes the xCreate() method to construct a new cache instance.
SQLite will typically create one cache instance for each open database file,
though this is not guaranteed. The
first parameter, szPage, is the size in bytes of the pages that must
be allocated by the cache. szPage will always a power of two. The
second parameter szExtra is a number of bytes of extra storage
associated with each page cache entry. The szExtra parameter will
a number less than 250. SQLite will use the
extra szExtra bytes on each page to store metadata about the underlying
database page on disk. The value passed into szExtra depends
on the SQLite version, the target platform, and how SQLite was compiled.
The third argument to xCreate(), bPurgeable, is true if the cache being
created will be used to cache database pages of a file stored on disk, or
false if it is used for an in-memory database. The cache implementation
does not have to do anything special based with the value of bPurgeable;
it is purely advisory. On a cache where bPurgeable is false, SQLite will
never invoke xUnpin() except to deliberately delete a page.
In other words, calls to xUnpin() on a cache with bPurgeable set to
false will always have the "discard" flag set to true.
Hence, a cache created with bPurgeable false will
never contain any unpinned pages.
The xCachesize() method may be called at any time by SQLite to set the
suggested maximum cache-size (number of pages stored by) the cache
instance passed as the first argument. This is the value configured using
the SQLite "PRAGMA cache_size
" command. As with the bPurgeable
parameter, the implementation is not required to do anything with this
value; it is advisory only.
The xPagecount() method must return the number of pages currently
stored in the cache, both pinned and unpinned.
The xFetch() method locates a page in the cache and returns a pointer to
an sqlite3_pcache_page object associated with that page, or a NULL pointer.
The pBuf element of the returned sqlite3_pcache_page object will be a
pointer to a buffer of szPage bytes used to store the content of a
single database page. The pExtra element of sqlite3_pcache_page will be
a pointer to the szExtra bytes of extra storage that SQLite has requested
for each entry in the page cache.
The page to be fetched is determined by the key. The minimum key value
is 1. After it has been retrieved using xFetch, the page is considered
to be "pinned".
If the requested page is already in the page cache, then the page cache
implementation must return a pointer to the page buffer with its content
intact. If the requested page is not already in the cache, then the
cache implementation should use the value of the createFlag
parameter to help it determined what action to take:
createFlag
Behaviour when page is not already in cache
0
Do not allocate a new page. Return NULL.
1
Allocate a new page if it easy and convenient to do so.
Otherwise return NULL.
2
Make every effort to allocate a new page. Only return
NULL if allocating a new page is effectively impossible.
SQLite will normally invoke xFetch() with a createFlag of 0 or 1. SQLite
will only use a createFlag of 2 after a prior call with a createFlag of 1
failed. In between the to xFetch() calls, SQLite may
attempt to unpin one or more cache pages by spilling the content of
pinned pages to disk and synching the operating system disk cache.
xUnpin() is called by SQLite with a pointer to a currently pinned page
as its second argument. If the third parameter, discard, is non-zero,
then the page must be evicted from the cache.
If the discard parameter is
zero, then the page may be discarded or retained at the discretion of
page cache implementation. The page cache implementation
may choose to evict unpinned pages at any time.
The cache must not perform any reference counting. A single
call to xUnpin() unpins the page regardless of the number of prior calls
to xFetch().
The xRekey() method is used to change the key value associated with the
page passed as the second argument. If the cache
previously contains an entry associated with newKey, it must be
discarded. Any prior cache entry associated with newKey is guaranteed not
to be pinned.
When SQLite calls the xTruncate() method, the cache must discard all
existing cache entries with page numbers (keys) greater than or equal
to the value of the iLimit parameter passed to xTruncate(). If any
of these pages are pinned, they are implicitly unpinned, meaning that
they can be safely discarded.
The xDestroy() method is used to delete a cache allocated by xCreate().
All resources associated with the specified cache should be freed. After
calling the xDestroy() method, SQLite considers the sqlite3_pcache*
handle invalid, and will not use it with any other sqlite3_pcache_methods2
functions.
SQLite invokes the xShrink() method when it wants the page cache to
free up as much of heap memory as possible. The page cache implementation
is not obligated to free any memory, but well-behaved implementations should
do their best.
SQL Statement Object
typedef struct sqlite3_stmt sqlite3_stmt;
An instance of this object represents a single SQL statement.
This object is variously known as a "prepared statement" or a
"compiled SQL statement" or simply as a "statement".
The life of a statement object goes something like this:
- Create the object using sqlite3_prepare_v2()
or a related
function.
- Bind values to host parameters
using the sqlite3_bind_*()
interfaces.
- Run the SQL by calling sqlite3_step()
one or more times.
- Reset the statement using sqlite3_reset()
then go back
to step 2. Do this zero or more times.
- Destroy the object using sqlite3_finalize()
.
Refer to documentation on individual methods above for additional
information.
Dynamically Typed Value Object
typedef struct Mem sqlite3_value;
SQLite uses the sqlite3_value object to represent all values
that can be stored in a database table. SQLite uses dynamic typing
for the values it stores. Values stored in sqlite3_value objects
can be integers, floating point values, strings, BLOBs, or NULL.
An sqlite3_value object may be either "protected" or "unprotected".
Some interfaces require a protected sqlite3_value. Other interfaces
will accept either a protected or an unprotected sqlite3_value.
Every interface that accepts sqlite3_value arguments specifies
whether or not it requires a protected sqlite3_value.
The terms "protected" and "unprotected" refer to whether or not
a mutex is held. An internal mutex is held for a protected
sqlite3_value object but no mutex is held for an unprotected
sqlite3_value object. If SQLite is compiled to be single-threaded
(with SQLITE_THREADSAFE=0
and with sqlite3_threadsafe()
returning 0)
or if SQLite is run in one of reduced mutex modes
SQLITE_CONFIG_SINGLETHREAD
or SQLITE_CONFIG_MULTITHREAD
then there is no distinction between protected and unprotected
sqlite3_value objects and they can be used interchangeably. However,
for maximum code portability it is recommended that applications
still make the distinction between protected and unprotected
sqlite3_value objects even when not strictly required.
The sqlite3_value objects that are passed as parameters into the
implementation of application-defined SQL functions
are protected.
The sqlite3_value object returned by
sqlite3_column_value()
is unprotected.
Unprotected sqlite3_value objects may only be used with
sqlite3_result_value()
and sqlite3_bind_value()
.
The sqlite3_value_type()
family of
interfaces require protected sqlite3_value objects.
Deprecated Functions
#ifndef SQLITE_OMIT_DEPRECATED
int sqlite3_aggregate_count(sqlite3_context*);
int sqlite3_expired(sqlite3_stmt*);
int sqlite3_transfer_bindings(sqlite3_stmt*, sqlite3_stmt*);
int sqlite3_global_recover(void);
void sqlite3_thread_cleanup(void);
int sqlite3_memory_alarm(void(*)(void*,sqlite3_int64,int),void*,sqlite3_int64);
#endif
These functions are deprecated
. In order to maintain
backwards compatibility with older code, these functions continue
to be supported. However, new applications should avoid
the use of these functions. To help encourage people to avoid
using these functions, we are not going to tell you what they do.
Online Backup API.
sqlite3_backup *sqlite3_backup_init(
sqlite3 *pDest, /* Destination database handle */
const char *zDestName, /* Destination database name */
sqlite3 *pSource, /* Source database handle */
const char *zSourceName /* Source database name */
);
int sqlite3_backup_step(sqlite3_backup *p, int nPage);
int sqlite3_backup_finish(sqlite3_backup *p);
int sqlite3_backup_remaining(sqlite3_backup *p);
int sqlite3_backup_pagecount(sqlite3_backup *p);
The backup API copies the content of one database into another.
It is useful either for creating backups of databases or
for copying in-memory databases to or from persistent files.
See Also: Using the SQLite Online Backup API
SQLite holds a write transaction open on the destination database file
for the duration of the backup operation.
The source database is read-locked only while it is being read;
it is not locked continuously for the entire backup operation.
Thus, the backup may be performed on a live source database without
preventing other database connections from
reading or writing to the source database while the backup is underway.
To perform a backup operation:
sqlite3_backup_init()
is called once to initialize the
backup,
sqlite3_backup_step()
is called one or more times to transfer
the data between the two databases, and finally
sqlite3_backup_finish()
is called to release all resources
associated with the backup operation.
There should be exactly one call to sqlite3_backup_finish() for each
successful call to sqlite3_backup_init().
sqlite3_backup_init()
The D and N arguments to sqlite3_backup_init(D,N,S,M) are the
database connection
associated with the destination database
and the database name, respectively.
The database name is "main" for the main database, "temp" for the
temporary database, or the name specified after the AS keyword in
an ATTACH
statement for an attached database.
The S and M arguments passed to
sqlite3_backup_init(D,N,S,M) identify the database connection
and database name of the source database, respectively.
The source and destination database connections
(parameters S and D)
must be different or else sqlite3_backup_init(D,N,S,M) will fail with
an error.
If an error occurs within sqlite3_backup_init(D,N,S,M), then NULL is
returned and an error code and error message are stored in the
destination database connection
D.
The error code and message for the failed call to sqlite3_backup_init()
can be retrieved using the sqlite3_errcode()
, sqlite3_errmsg()
, and/or
sqlite3_errmsg16()
functions.
A successful call to sqlite3_backup_init() returns a pointer to an
sqlite3_backup
object.
The sqlite3_backup
object may be used with the sqlite3_backup_step() and
sqlite3_backup_finish() functions to perform the specified backup
operation.
sqlite3_backup_step()
Function sqlite3_backup_step(B,N) will copy up to N pages between
the source and destination databases specified by sqlite3_backup
object B.
If N is negative, all remaining source pages are copied.
If sqlite3_backup_step(B,N) successfully copies N pages and there
are still more pages to be copied, then the function returns SQLITE_OK
.
If sqlite3_backup_step(B,N) successfully finishes copying all pages
from source to destination, then it returns SQLITE_DONE
.
If an error occurs while running sqlite3_backup_step(B,N),
then an error code
is returned. As well as SQLITE_OK
and
SQLITE_DONE
, a call to sqlite3_backup_step() may return SQLITE_READONLY
,
SQLITE_NOMEM
, SQLITE_BUSY
, SQLITE_LOCKED
, or an
SQLITE_IOERR_XXX
extended error code.
The sqlite3_backup_step() might return SQLITE_READONLY
if
- the destination database was opened read-only, or
- the destination database is using write-ahead-log journaling
and the destination and source page sizes differ, or
- the destination database is an in-memory database and the
destination and source page sizes differ.
If sqlite3_backup_step() cannot obtain a required file-system lock, then
the busy-handler function
is invoked (if one is specified). If the
busy-handler returns non-zero before the lock is available, then
SQLITE_BUSY
is returned to the caller. In this case the call to
sqlite3_backup_step() can be retried later. If the source
database connection
is being used to write to the source database when sqlite3_backup_step()
is called, then SQLITE_LOCKED
is returned immediately. Again, in this
case the call to sqlite3_backup_step() can be retried later on. If
SQLITE_IOERR_XXX
, SQLITE_NOMEM
, or
SQLITE_READONLY
is returned, then
there is no point in retrying the call to sqlite3_backup_step(). These
errors are considered fatal. The application must accept
that the backup operation has failed and pass the backup operation handle
to the sqlite3_backup_finish() to release associated resources.
The first call to sqlite3_backup_step() obtains an exclusive lock
on the destination file. The exclusive lock is not released until either
sqlite3_backup_finish() is called or the backup operation is complete
and sqlite3_backup_step() returns SQLITE_DONE
. Every call to
sqlite3_backup_step() obtains a shared lock
on the source database that
lasts for the duration of the sqlite3_backup_step() call.
Because the source database is not locked between calls to
sqlite3_backup_step(), the source database may be modified mid-way
through the backup process. If the source database is modified by an
external process or via a database connection other than the one being
used by the backup operation, then the backup will be automatically
restarted by the next call to sqlite3_backup_step(). If the source
database is modified by the using the same database connection as is used
by the backup operation, then the backup database is automatically
updated at the same time.
sqlite3_backup_finish()
When sqlite3_backup_step() has returned SQLITE_DONE
, or when the
application wishes to abandon the backup operation, the application
should destroy the sqlite3_backup
by passing it to sqlite3_backup_finish().
The sqlite3_backup_finish() interfaces releases all
resources associated with the sqlite3_backup
object.
If sqlite3_backup_step() has not yet returned SQLITE_DONE
, then any
active write-transaction on the destination database is rolled back.
The sqlite3_backup
object is invalid
and may not be used following a call to sqlite3_backup_finish().
The value returned by sqlite3_backup_finish is SQLITE_OK
if no
sqlite3_backup_step() errors occurred, regardless or whether or not
sqlite3_backup_step() completed.
If an out-of-memory condition or IO error occurred during any prior
sqlite3_backup_step() call on the same sqlite3_backup
object, then
sqlite3_backup_finish() returns the corresponding error code
.
A return of SQLITE_BUSY
or SQLITE_LOCKED
from sqlite3_backup_step()
is not a permanent error and does not affect the return value of
sqlite3_backup_finish().
sqlite3_backup_remaining() and sqlite3_backup_pagecount()
Each call to sqlite3_backup_step() sets two values inside
the sqlite3_backup
object: the number of pages still to be backed
up and the total number of pages in the source database file.
The sqlite3_backup_remaining() and sqlite3_backup_pagecount() interfaces
retrieve these two values, respectively.
The values returned by these functions are only updated by
sqlite3_backup_step(). If the source database is modified during a backup
operation, then the values are not updated to account for any extra
pages that need to be updated or the size of the source database file
changing.
Concurrent Usage of Database Handles
The source database connection
may be used by the application for other
purposes while a backup operation is underway or being initialized.
If SQLite is compiled and configured to support threadsafe database
connections, then the source database connection may be used concurrently
from within other threads.
However, the application must guarantee that the destination
database connection
is not passed to any other API (by any thread) after
sqlite3_backup_init() is called and before the corresponding call to
sqlite3_backup_finish(). SQLite does not currently check to see
if the application incorrectly accesses the destination database connection
and so no error code is reported, but the operations may malfunction
nevertheless. Use of the destination database connection while a
backup is in progress might also also cause a mutex deadlock.
If running in shared cache mode
, the application must
guarantee that the shared cache used by the destination database
is not accessed while the backup is running. In practice this means
that the application must guarantee that the disk file being
backed up to is not accessed by any connection within the process,
not just the specific connection that was passed to sqlite3_backup_init().
The sqlite3_backup
object itself is partially threadsafe. Multiple
threads may safely make multiple concurrent calls to sqlite3_backup_step().
However, the sqlite3_backup_remaining() and sqlite3_backup_pagecount()
APIs are not strictly speaking threadsafe. If they are invoked at the
same time as another thread is invoking sqlite3_backup_step() it is
possible that they return invalid values.
Collation Needed Callbacks
int sqlite3_collation_needed(
sqlite3*,
void*,
void(*)(void*,sqlite3*,int eTextRep,const char*)
);
int sqlite3_collation_needed16(
sqlite3*,
void*,
void(*)(void*,sqlite3*,int eTextRep,const void*)
);
To avoid having to register all collation sequences before a database
can be used, a single callback function may be registered with the
database connection
to be invoked whenever an undefined collation
sequence is required.
If the function is registered using the sqlite3_collation_needed() API,
then it is passed the names of undefined collation sequences as strings
encoded in UTF-8. If sqlite3_collation_needed16() is used,
the names are passed as UTF-16 in machine native byte order.
A call to either function replaces the existing collation-needed callback.
When the callback is invoked, the first argument passed is a copy
of the second argument to sqlite3_collation_needed() or
sqlite3_collation_needed16(). The second argument is the database
connection. The third argument is one of SQLITE_UTF8
, SQLITE_UTF16BE
,
or SQLITE_UTF16LE
, indicating the most desirable form of the collation
sequence function required. The fourth parameter is the name of the
required collation sequence.
The callback function should register the desired collation using
sqlite3_create_collation()
, sqlite3_create_collation16()
, or
sqlite3_create_collation_v2()
.
Source Of Data In A Query Result
const char *sqlite3_column_database_name(sqlite3_stmt*,int);
const void *sqlite3_column_database_name16(sqlite3_stmt*,int);
const char *sqlite3_column_table_name(sqlite3_stmt*,int);
const void *sqlite3_column_table_name16(sqlite3_stmt*,int);
const char *sqlite3_column_origin_name(sqlite3_stmt*,int);
const void *sqlite3_column_origin_name16(sqlite3_stmt*,int);
These routines provide a means to determine the database, table, and
table column that is the origin of a particular result column in
SELECT
statement.
The name of the database or table or column can be returned as
either a UTF-8 or UTF-16 string. The _database_ routines return
the database name, the _table_ routines return the table name, and
the origin_ routines return the column name.
The returned string is valid until the prepared statement
is destroyed
using sqlite3_finalize()
or until the statement is automatically
reprepared by the first call to sqlite3_step()
for a particular run
or until the same information is requested
again in a different encoding.
The names returned are the original un-aliased names of the
database, table, and column.
The first argument to these interfaces is a prepared statement
.
These functions return information about the Nth result column returned by
the statement, where N is the second function argument.
The left-most column is column 0 for these routines.
If the Nth column returned by the statement is an expression or
subquery and is not a column value, then all of these functions return
NULL. These routine might also return NULL if a memory allocation error
occurs. Otherwise, they return the name of the attached database, table,
or column that query result column was extracted from.
As with all other SQLite APIs, those whose names end with "16" return
UTF-16 encoded strings and the other functions return UTF-8.
These APIs are only available if the library was compiled with the
SQLITE_ENABLE_COLUMN_METADATA
C-preprocessor symbol.
If two or more threads call one or more of these routines against the same
prepared statement and column at the same time then the results are
undefined.
If two or more threads call one or more
column metadata interfaces
for the same prepared statement
and result column
at the same time then the results are undefined.
Declared Datatype Of A Query Result
const char *sqlite3_column_decltype(sqlite3_stmt*,int);
const void *sqlite3_column_decltype16(sqlite3_stmt*,int);
The first parameter is a prepared statement
.
If this statement is a SELECT
statement and the Nth column of the
returned result set of that SELECT
is a table column (not an
expression or subquery) then the declared type of the table
column is returned. If the Nth column of the result set is an
expression or subquery, then a NULL pointer is returned.
The returned string is always UTF-8 encoded.
For example, given the database schema:
CREATE TABLE t1(c1 VARIANT);
and the following statement to be compiled:
SELECT c1 + 1, c1 FROM t1;
this routine would return the string "VARIANT" for the second result
column (i==1), and a NULL pointer for the first result column (i==0).
SQLite uses dynamic run-time typing. So just because a column
is declared to contain a particular type does not mean that the
data stored in that column is of the declared type. SQLite is
strongly typed, but the typing is dynamic not static. Type
is associated with individual values, not with the containers
used to hold those values.
Column Names In A Result Set
const char *sqlite3_column_name(sqlite3_stmt*, int N);
const void *sqlite3_column_name16(sqlite3_stmt*, int N);
These routines return the name assigned to a particular column
in the result set of a SELECT
statement. The sqlite3_column_name()
interface returns a pointer to a zero-terminated UTF-8 string
and sqlite3_column_name16() returns a pointer to a zero-terminated
UTF-16 string. The first parameter is the prepared statement
that implements the SELECT
statement. The second parameter is the
column number. The leftmost column is number 0.
The returned string pointer is valid until either the prepared statement
is destroyed by sqlite3_finalize()
or until the statement is automatically
reprepared by the first call to sqlite3_step()
for a particular run
or until the next call to
sqlite3_column_name() or sqlite3_column_name16() on the same column.
If sqlite3_malloc() fails during the processing of either routine
(for example during a conversion from UTF-8 to UTF-16) then a
NULL pointer is returned.
The name of a result column is the value of the "AS" clause for
that column, if there is an AS clause. If there is no AS clause
then the name of the column is unspecified and may change from
one release of SQLite to the next.
Commit And Rollback Notification Callbacks
void *sqlite3_commit_hook(sqlite3*, int(*)(void*), void*);
void *sqlite3_rollback_hook(sqlite3*, void(*)(void *), void*);
The sqlite3_commit_hook() interface registers a callback
function to be invoked whenever a transaction is committed
.
Any callback set by a previous call to sqlite3_commit_hook()
for the same database connection is overridden.
The sqlite3_rollback_hook() interface registers a callback
function to be invoked whenever a transaction is rolled back
.
Any callback set by a previous call to sqlite3_rollback_hook()
for the same database connection is overridden.
The pArg argument is passed through to the callback.
If the callback on a commit hook function returns non-zero,
then the commit is converted into a rollback.
The sqlite3_commit_hook(D,C,P) and sqlite3_rollback_hook(D,C,P) functions
return the P argument from the previous call of the same function
on the same database connection
D, or NULL for
the first call for each function on D.
The commit and rollback hook callbacks are not reentrant.
The callback implementation must not do anything that will modify
the database connection that invoked the callback. Any actions
to modify the database connection must be deferred until after the
completion of the sqlite3_step()
call that triggered the commit
or rollback hook in the first place.
Note that running any other SQL statements, including SELECT statements,
or merely calling sqlite3_prepare_v2()
and sqlite3_step()
will modify
the database connections for the meaning of "modify" in this paragraph.
Registering a NULL function disables the callback.
When the commit hook callback routine returns zero, the COMMIT
operation is allowed to continue normally. If the commit hook
returns non-zero, then the COMMIT
is converted into a ROLLBACK
.
The rollback hook is invoked on a rollback that results from a commit
hook returning non-zero, just as it would be with any other rollback.
For the purposes of this API, a transaction is said to have been
rolled back if an explicit "ROLLBACK" statement is executed, or
an error or constraint causes an implicit rollback to occur.
The rollback callback is not invoked if a transaction is
automatically rolled back because the database connection is closed.
See also the sqlite3_update_hook()
interface.
Run-Time Library Compilation Options Diagnostics
#ifndef SQLITE_OMIT_COMPILEOPTION_DIAGS
int sqlite3_compileoption_used(const char *zOptName);
const char *sqlite3_compileoption_get(int N);
#endif
The sqlite3_compileoption_used() function returns 0 or 1
indicating whether the specified option was defined at
compile time. The SQLITE_ prefix may be omitted from the
option name passed to sqlite3_compileoption_used().
The sqlite3_compileoption_get() function allows iterating
over the list of options that were defined at compile time by
returning the N-th compile time option string. If N is out of range,
sqlite3_compileoption_get() returns a NULL pointer. The SQLITE_
prefix is omitted from any strings returned by
sqlite3_compileoption_get().
Support for the diagnostic functions sqlite3_compileoption_used()
and sqlite3_compileoption_get() may be omitted by specifying the
SQLITE_OMIT_COMPILEOPTION_DIAGS
option at compile time.
See also: SQL functions sqlite_compileoption_used()
and
sqlite_compileoption_get()
and the compile_options pragma
.
Determine If An SQL Statement Is Complete
int sqlite3_complete(const char *sql);
int sqlite3_complete16(const void *sql);
These routines are useful during command-line input to determine if the
currently entered text seems to form a complete SQL statement or
if additional input is needed before sending the text into
SQLite for parsing. These routines return 1 if the input string
appears to be a complete SQL statement. A statement is judged to be
complete if it ends with a semicolon token and is not a prefix of a
well-formed CREATE TRIGGER statement. Semicolons that are embedded within
string literals or quoted identifier names or comments are not
independent tokens (they are part of the token in which they are
embedded) and thus do not count as a statement terminator. Whitespace
and comments that follow the final semicolon are ignored.
These routines return 0 if the statement is incomplete. If a
memory allocation fails, then SQLITE_NOMEM is returned.
These routines do not parse the SQL statements thus
will not detect syntactically incorrect SQL.
If SQLite has not been initialized using sqlite3_initialize()
prior
to invoking sqlite3_complete16() then sqlite3_initialize() is invoked
automatically by sqlite3_complete16(). If that initialization fails,
then the return value from sqlite3_complete16() will be non-zero
regardless of whether or not the input SQL is complete.
The input to sqlite3_complete()
must be a zero-terminated
UTF-8 string.
The input to sqlite3_complete16()
must be a zero-terminated
UTF-16 string in native byte order.
Define New Collating Sequences
int sqlite3_create_collation(
sqlite3*,
const char *zName,
int eTextRep,
void *pArg,
int(*xCompare)(void*,int,const void*,int,const void*)
);
int sqlite3_create_collation_v2(
sqlite3*,
const char *zName,
int eTextRep,
void *pArg,
int(*xCompare)(void*,int,const void*,int,const void*),
void(*xDestroy)(void*)
);
int sqlite3_create_collation16(
sqlite3*,
const void *zName,
int eTextRep,
void *pArg,
int(*xCompare)(void*,int,const void*,int,const void*)
);
These functions add, remove, or modify a collation
associated
with the database connection
specified as the first argument.
The name of the collation is a UTF-8 string
for sqlite3_create_collation() and sqlite3_create_collation_v2()
and a UTF-16 string in native byte order for sqlite3_create_collation16().
Collation names that compare equal according to sqlite3_strnicmp()
are
considered to be the same name.
The third argument (eTextRep) must be one of the constants:
- SQLITE_UTF8
,
- SQLITE_UTF16LE
,
- SQLITE_UTF16BE
,
- SQLITE_UTF16
, or
- SQLITE_UTF16_ALIGNED
.
The eTextRep argument determines the encoding of strings passed
to the collating function callback, xCallback.
The SQLITE_UTF16
and SQLITE_UTF16_ALIGNED
values for eTextRep
force strings to be UTF16 with native byte order.
The SQLITE_UTF16_ALIGNED
value for eTextRep forces strings to begin
on an even byte address.
The fourth argument, pArg, is an application data pointer that is passed
through as the first argument to the collating function callback.
The fifth argument, xCallback, is a pointer to the collating function.
Multiple collating functions can be registered using the same name but
with different eTextRep parameters and SQLite will use whichever
function requires the least amount of data transformation.
If the xCallback argument is NULL then the collating function is
deleted. When all collating functions having the same name are deleted,
that collation is no longer usable.
The collating function callback is invoked with a copy of the pArg
application data pointer and with two strings in the encoding specified
by the eTextRep argument. The collating function must return an
integer that is negative, zero, or positive
if the first string is less than, equal to, or greater than the second,
respectively. A collating function must always return the same answer
given the same inputs. If two or more collating functions are registered
to the same collation name (using different eTextRep values) then all
must give an equivalent answer when invoked with equivalent strings.
The collating function must obey the following properties for all
strings A, B, and C:
- If A==B then B==A.
- If A==B and B==C then A==C.
- If A<B THEN B>A.
- If A<B and B<C then A<C.
If a collating function fails any of the above constraints and that
collating function is registered and used, then the behavior of SQLite
is undefined.
The sqlite3_create_collation_v2() works like sqlite3_create_collation()
with the addition that the xDestroy callback is invoked on pArg when
the collating function is deleted.
Collating functions are deleted when they are overridden by later
calls to the collation creation functions or when the
database connection
is closed using sqlite3_close()
.
The xDestroy callback is not
called if the
sqlite3_create_collation_v2() function fails. Applications that invoke
sqlite3_create_collation_v2() with a non-NULL xDestroy argument should
check the return code and dispose of the application data pointer
themselves rather than expecting SQLite to deal with it for them.
This is different from every other SQLite interface. The inconsistency
is unfortunate but cannot be changed without breaking backwards
compatibility.
See also: sqlite3_collation_needed()
and sqlite3_collation_needed16()
.
Register A Virtual Table Implementation
int sqlite3_create_module(
sqlite3 *db, /* SQLite connection to register module with */
const char *zName, /* Name of the module */
const sqlite3_module *p, /* Methods for the module */
void *pClientData /* Client data for xCreate/xConnect */
);
int sqlite3_create_module_v2(
sqlite3 *db, /* SQLite connection to register module with */
const char *zName, /* Name of the module */
const sqlite3_module *p, /* Methods for the module */
void *pClientData, /* Client data for xCreate/xConnect */
void(*xDestroy)(void*) /* Module destructor function */
);
These routines are used to register a new virtual table module
name.
Module names must be registered before
creating a new virtual table
using the module and before using a
preexisting virtual table
for the module.
The module name is registered on the database connection
specified
by the first parameter. The name of the module is given by the
second parameter. The third parameter is a pointer to
the implementation of the virtual table module
. The fourth
parameter is an arbitrary client data pointer that is passed through
into the xCreate
and xConnect
methods of the virtual table module
when a new virtual table is be being created or reinitialized.
The sqlite3_create_module_v2() interface has a fifth parameter which
is a pointer to a destructor for the pClientData. SQLite will
invoke the destructor function (if it is not NULL) when SQLite
no longer needs the pClientData pointer. The destructor will also
be invoked if the call to sqlite3_create_module_v2() fails.
The sqlite3_create_module()
interface is equivalent to sqlite3_create_module_v2() with a NULL
destructor.
Error Codes And Messages
int sqlite3_errcode(sqlite3 *db);
int sqlite3_extended_errcode(sqlite3 *db);
const char *sqlite3_errmsg(sqlite3*);
const void *sqlite3_errmsg16(sqlite3*);
The sqlite3_errcode() interface returns the numeric result code
or
extended result code
for the most recent failed sqlite3_* API call
associated with a database connection
. If a prior API call failed
but the most recent API call succeeded, the return value from
sqlite3_errcode() is undefined. The sqlite3_extended_errcode()
interface is the same except that it always returns the
extended result code
even when extended result codes are
disabled.
The sqlite3_errmsg() and sqlite3_errmsg16() return English-language
text that describes the error, as either UTF-8 or UTF-16 respectively.
Memory to hold the error message string is managed internally.
The application does not need to worry about freeing the result.
However, the error string might be overwritten or deallocated by
subsequent calls to other SQLite interface functions.
When the serialized threading mode
is in use, it might be the
case that a second error occurs on a separate thread in between
the time of the first error and the call to these interfaces.
When that happens, the second error will be reported since these
interfaces always report the most recent result. To avoid
this, each thread can obtain exclusive use of the database connection
D
by invoking sqlite3_mutex_enter
(sqlite3_db_mutex
(D)) before beginning
to use D and invoking sqlite3_mutex_leave
(sqlite3_db_mutex
(D)) after
all calls to the interfaces listed here are completed.
If an interface fails with SQLITE_MISUSE, that means the interface
was invoked incorrectly by the application. In that case, the
error code and message may or may not be set.
Memory Allocation Subsystem
void *sqlite3_malloc(int);
void *sqlite3_realloc(void*, int);
void sqlite3_free(void*);
The SQLite core uses these three routines for all of its own
internal memory allocation needs. "Core" in the previous sentence
does not include operating-system specific VFS implementation. The
Windows VFS uses native malloc() and free() for some operations.
The sqlite3_malloc() routine returns a pointer to a block
of memory at least N bytes in length, where N is the parameter.
If sqlite3_malloc() is unable to obtain sufficient free
memory, it returns a NULL pointer. If the parameter N to
sqlite3_malloc() is zero or negative then sqlite3_malloc() returns
a NULL pointer.
Calling sqlite3_free() with a pointer previously returned
by sqlite3_malloc() or sqlite3_realloc() releases that memory so
that it might be reused. The sqlite3_free() routine is
a no-op if is called with a NULL pointer. Passing a NULL pointer
to sqlite3_free() is harmless. After being freed, memory
should neither be read nor written. Even reading previously freed
memory might result in a segmentation fault or other severe error.
Memory corruption, a segmentation fault, or other severe error
might result if sqlite3_free() is called with a non-NULL pointer that
was not obtained from sqlite3_malloc() or sqlite3_realloc().
The sqlite3_realloc() interface attempts to resize a
prior memory allocation to be at least N bytes, where N is the
second parameter. The memory allocation to be resized is the first
parameter. If the first parameter to sqlite3_realloc()
is a NULL pointer then its behavior is identical to calling
sqlite3_malloc(N) where N is the second parameter to sqlite3_realloc().
If the second parameter to sqlite3_realloc() is zero or
negative then the behavior is exactly the same as calling
sqlite3_free(P) where P is the first parameter to sqlite3_realloc().
sqlite3_realloc() returns a pointer to a memory allocation
of at least N bytes in size or NULL if sufficient memory is unavailable.
If M is the size of the prior allocation, then min(N,M) bytes
of the prior allocation are copied into the beginning of buffer returned
by sqlite3_realloc() and the prior allocation is freed.
If sqlite3_realloc() returns NULL, then the prior allocation
is not freed.
The memory returned by sqlite3_malloc() and sqlite3_realloc()
is always aligned to at least an 8 byte boundary, or to a
4 byte boundary if the SQLITE_4_BYTE_ALIGNED_MALLOC
compile-time
option is used.
In SQLite version 3.5.0 and 3.5.1, it was possible to define
the SQLITE_OMIT_MEMORY_ALLOCATION which would cause the built-in
implementation of these routines to be omitted. That capability
is no longer provided. Only built-in memory allocators can be used.
The Windows OS interface layer calls
the system malloc() and free() directly when converting
filenames between the UTF-8 encoding used by SQLite
and whatever filename encoding is used by the particular Windows
installation. Memory allocation errors are detected, but
they are reported back as SQLITE_CANTOPEN
or
SQLITE_IOERR
rather than SQLITE_NOMEM
.
The pointer arguments to sqlite3_free()
and sqlite3_realloc()
must be either NULL or else pointers obtained from a prior
invocation of sqlite3_malloc()
or sqlite3_realloc()
that have
not yet been released.
The application must not read or write any part of
a block of memory after it has been released using
sqlite3_free()
or sqlite3_realloc()
.
Convenience Routines For Running Queries
int sqlite3_get_table(
sqlite3 *db, /* An open database */
const char *zSql, /* SQL to be evaluated */
char ***pazResult, /* Results of the query */
int *pnRow, /* Number of result rows written here */
int *pnColumn, /* Number of result columns written here */
char **pzErrmsg /* Error msg written here */
);
void sqlite3_free_table(char **result);
This is a legacy interface that is preserved for backwards compatibility.
Use of this interface is not recommended.
Definition: A result table
is memory data structure created by the
sqlite3_get_table()
interface. A result table records the
complete query results from one or more queries.
The table conceptually has a number of rows and columns. But
these numbers are not part of the result table itself. These
numbers are obtained separately. Let N be the number of rows
and M be the number of columns.
A result table is an array of pointers to zero-terminated UTF-8 strings.
There are (N+1)*M elements in the array. The first M pointers point
to zero-terminated strings that contain the names of the columns.
The remaining entries all point to query results. NULL values result
in NULL pointers. All other values are in their UTF-8 zero-terminated
string representation as returned by sqlite3_column_text()
.
A result table might consist of one or more memory allocations.
It is not safe to pass a result table directly to sqlite3_free()
.
A result table should be deallocated using sqlite3_free_table()
.
As an example of the result table format, suppose a query result
is as follows:
Name | Age
-----------------------
Alice | 43
Bob | 28
Cindy | 21
There are two column (M==2) and three rows (N==3). Thus the
result table has 8 entries. Suppose the result table is stored
in an array names azResult. Then azResult holds this content:
azResult[0] = "Name";
azResult[1] = "Age";
azResult[2] = "Alice";
azResult[3] = "43";
azResult[4] = "Bob";
azResult[5] = "28";
azResult[6] = "Cindy";
azResult[7] = "21";
The sqlite3_get_table() function evaluates one or more
semicolon-separated SQL statements in the zero-terminated UTF-8
string of its 2nd parameter and returns a result table to the
pointer given in its 3rd parameter.
After the application has finished with the result from sqlite3_get_table(),
it must pass the result table pointer to sqlite3_free_table() in order to
release the memory that was malloced. Because of the way the
sqlite3_malloc()
happens within sqlite3_get_table(), the calling
function must not try to call sqlite3_free()
directly. Only
sqlite3_free_table()
is able to release the memory properly and safely.
The sqlite3_get_table() interface is implemented as a wrapper around
sqlite3_exec()
. The sqlite3_get_table() routine does not have access
to any internal data structures of SQLite. It uses only the public
interface defined here. As a consequence, errors that occur in the
wrapper layer outside of the internal sqlite3_exec()
call are not
reflected in subsequent calls to sqlite3_errcode()
or
sqlite3_errmsg()
.
Function Auxiliary Data
void *sqlite3_get_auxdata(sqlite3_context*, int N);
void sqlite3_set_auxdata(sqlite3_context*, int N, void*, void (*)(void*));
The following two functions may be used by scalar SQL functions to
associate metadata with argument values. If the same value is passed to
multiple invocations of the same SQL function during query execution, under
some circumstances the associated metadata may be preserved. This may
be used, for example, to add a regular-expression matching scalar
function. The compiled version of the regular expression is stored as
metadata associated with the SQL value passed as the regular expression
pattern. The compiled regular expression can be reused on multiple
invocations of the same function so that the original pattern string
does not need to be recompiled on each invocation.
The sqlite3_get_auxdata() interface returns a pointer to the metadata
associated by the sqlite3_set_auxdata() function with the Nth argument
value to the application-defined function. If no metadata has been ever
been set for the Nth argument of the function, or if the corresponding
function parameter has changed since the meta-data was set,
then sqlite3_get_auxdata() returns a NULL pointer.
The sqlite3_set_auxdata() interface saves the metadata
pointed to by its 3rd parameter as the metadata for the N-th
argument of the application-defined function. Subsequent
calls to sqlite3_get_auxdata() might return this data, if it has
not been destroyed.
If it is not NULL, SQLite will invoke the destructor
function given by the 4th parameter to sqlite3_set_auxdata() on
the metadata when the corresponding function parameter changes
or when the SQL statement completes, whichever comes first.
SQLite is free to call the destructor and drop metadata on any
parameter of any function at any time. The only guarantee is that
the destructor will be called before the metadata is dropped.
In practice, metadata is preserved between function calls for
expressions that are constant at compile time. This includes literal
values and parameters
.
These routines must be called from the same thread in which
the SQL function is running.
Initialize The SQLite Library
int sqlite3_initialize(void);
int sqlite3_shutdown(void);
int sqlite3_os_init(void);
int sqlite3_os_end(void);
The sqlite3_initialize() routine initializes the
SQLite library. The sqlite3_shutdown() routine
deallocates any resources that were allocated by sqlite3_initialize().
These routines are designed to aid in process initialization and
shutdown on embedded systems. Workstation applications using
SQLite normally do not need to invoke either of these routines.
A call to sqlite3_initialize() is an "effective" call if it is
the first time sqlite3_initialize() is invoked during the lifetime of
the process, or if it is the first time sqlite3_initialize() is invoked
following a call to sqlite3_shutdown(). Only an effective call
of sqlite3_initialize() does any initialization. All other calls
are harmless no-ops.
A call to sqlite3_shutdown() is an "effective" call if it is the first
call to sqlite3_shutdown() since the last sqlite3_initialize(). Only
an effective call to sqlite3_shutdown() does any deinitialization.
All other valid calls to sqlite3_shutdown() are harmless no-ops.
The sqlite3_initialize() interface is threadsafe, but sqlite3_shutdown()
is not. The sqlite3_shutdown() interface must only be called from a
single thread. All open database connections
must be closed and all
other SQLite resources must be deallocated prior to invoking
sqlite3_shutdown().
Among other things, sqlite3_initialize() will invoke
sqlite3_os_init(). Similarly, sqlite3_shutdown()
will invoke sqlite3_os_end().
The sqlite3_initialize() routine returns SQLITE_OK
on success.
If for some reason, sqlite3_initialize() is unable to initialize
the library (perhaps it is unable to allocate a needed resource such
as a mutex) it returns an error code
other than SQLITE_OK
.
The sqlite3_initialize() routine is called internally by many other
SQLite interfaces so that an application usually does not need to
invoke sqlite3_initialize() directly. For example, sqlite3_open()
calls sqlite3_initialize() so the SQLite library will be automatically
initialized when sqlite3_open()
is called if it has not be initialized
already. However, if SQLite is compiled with the SQLITE_OMIT_AUTOINIT
compile-time option, then the automatic calls to sqlite3_initialize()
are omitted and the application must call sqlite3_initialize() directly
prior to using any other SQLite interface. For maximum portability,
it is recommended that applications always invoke sqlite3_initialize()
directly prior to using any other SQLite interface. Future releases
of SQLite may require this. In other words, the behavior exhibited
when SQLite is compiled with SQLITE_OMIT_AUTOINIT
might become the
default behavior in some future release of SQLite.
The sqlite3_os_init() routine does operating-system specific
initialization of the SQLite library. The sqlite3_os_end()
routine undoes the effect of sqlite3_os_init(). Typical tasks
performed by these routines include allocation or deallocation
of static resources, initialization of global variables,
setting up a default sqlite3_vfs
module, or setting up
a default configuration using sqlite3_config()
.
The application should never invoke either sqlite3_os_init()
or sqlite3_os_end() directly. The application should only invoke
sqlite3_initialize() and sqlite3_shutdown(). The sqlite3_os_init()
interface is called automatically by sqlite3_initialize() and
sqlite3_os_end() is called by sqlite3_shutdown(). Appropriate
implementations for sqlite3_os_init() and sqlite3_os_end()
are built into SQLite when it is compiled for Unix, Windows, or OS/2.
When built for other platforms
(using the SQLITE_OS_OTHER=1
compile-time
option) the application must supply a suitable implementation for
sqlite3_os_init() and sqlite3_os_end(). An application-supplied
implementation of sqlite3_os_init() or sqlite3_os_end()
must return SQLITE_OK
on success and some other error code
upon
failure.
Run-Time Library Version Numbers
SQLITE_EXTERN const char sqlite3_version[];
const char *sqlite3_libversion(void);
const char *sqlite3_sourceid(void);
int sqlite3_libversion_number(void);
These interfaces provide the same information as the SQLITE_VERSION
,
SQLITE_VERSION_NUMBER
, and SQLITE_SOURCE_ID
C preprocessor macros
but are associated with the library instead of the header file. Cautious
programmers might include assert() statements in their application to
verify that values returned by these interfaces match the macros in
the header, and thus insure that the application is
compiled with matching library and header files.
assert( sqlite3_libversion_number()==SQLITE_VERSION_NUMBER );
assert( strcmp(sqlite3_sourceid(),SQLITE_SOURCE_ID)==0 );
assert( strcmp(sqlite3_libversion(),SQLITE_VERSION)==0 );
The sqlite3_version[] string constant contains the text of SQLITE_VERSION
macro. The sqlite3_libversion() function returns a pointer to the
to the sqlite3_version[] string constant. The sqlite3_libversion()
function is provided for use in DLLs since DLL users usually do not have
direct access to string constants within the DLL. The
sqlite3_libversion_number() function returns an integer equal to
SQLITE_VERSION_NUMBER
. The sqlite3_sourceid() function returns
a pointer to a string constant whose value is the same as the
SQLITE_SOURCE_ID
C preprocessor macro.
See also: sqlite_version()
and sqlite_source_id()
.
Memory Allocator Statistics
sqlite3_int64 sqlite3_memory_used(void);
sqlite3_int64 sqlite3_memory_highwater(int resetFlag);
SQLite provides these two interfaces for reporting on the status
of the sqlite3_malloc()
, sqlite3_free()
, and sqlite3_realloc()
routines, which form the built-in memory allocation subsystem.
The sqlite3_memory_used()
routine returns the number of bytes
of memory currently outstanding (malloced but not freed).
The sqlite3_memory_highwater()
routine returns the maximum
value of sqlite3_memory_used()
since the high-water mark
was last reset. The values returned by sqlite3_memory_used()
and
sqlite3_memory_highwater()
include any overhead
added by SQLite in its implementation of sqlite3_malloc()
,
but not overhead added by the any underlying system library
routines that sqlite3_malloc()
may call.
The memory high-water mark is reset to the current value of
sqlite3_memory_used()
if and only if the parameter to
sqlite3_memory_highwater()
is true. The value returned
by sqlite3_memory_highwater(1)
is the high-water mark
prior to the reset.
Formatted String Printing Functions
char *sqlite3_mprintf(const char*,...);
char *sqlite3_vmprintf(const char*, va_list);
char *sqlite3_snprintf(int,char*,const char*, ...);
char *sqlite3_vsnprintf(int,char*,const char*, va_list);
These routines are work-alikes of the "printf()" family of functions
from the standard C library.
The sqlite3_mprintf() and sqlite3_vmprintf() routines write their
results into memory obtained from sqlite3_malloc()
.
The strings returned by these two routines should be
released by sqlite3_free()
. Both routines return a
NULL pointer if sqlite3_malloc()
is unable to allocate enough
memory to hold the resulting string.
The sqlite3_snprintf() routine is similar to "snprintf()" from
the standard C library. The result is written into the
buffer supplied as the second parameter whose size is given by
the first parameter. Note that the order of the
first two parameters is reversed from snprintf(). This is an
historical accident that cannot be fixed without breaking
backwards compatibility. Note also that sqlite3_snprintf()
returns a pointer to its buffer instead of the number of
characters actually written into the buffer. We admit that
the number of characters written would be a more useful return
value but we cannot change the implementation of sqlite3_snprintf()
now without breaking compatibility.
As long as the buffer size is greater than zero, sqlite3_snprintf()
guarantees that the buffer is always zero-terminated. The first
parameter "n" is the total size of the buffer, including space for
the zero terminator. So the longest string that can be completely
written will be n-1 characters.
The sqlite3_vsnprintf() routine is a varargs version of sqlite3_snprintf().
These routines all implement some additional formatting
options that are useful for constructing SQL statements.
All of the usual printf() formatting options apply. In addition, there
is are "%q", "%Q", and "%z" options.
The %q option works like %s in that it substitutes a nul-terminated
string from the argument list. But %q also doubles every '\'' character.
%q is designed for use inside a string literal. By doubling each '\''
character it escapes that character and allows it to be inserted into
the string.
For example, assume the string variable zText contains text as follows:
char *zText = "It's a happy day!";
One can use this text in an SQL statement as follows:
char *zSQL = sqlite3_mprintf("INSERT INTO table VALUES('%q')", zText);
sqlite3_exec(db, zSQL, 0, 0, 0);
sqlite3_free(zSQL);
Because the %q format string is used, the '\'' character in zText
is escaped and the SQL generated is as follows:
INSERT INTO table1 VALUES('It''s a happy day!')
This is correct. Had we used %s instead of %q, the generated SQL
would have looked like this:
INSERT INTO table1 VALUES('It's a happy day!');
This second example is an SQL syntax error. As a general rule you should
always use %q instead of %s when inserting text into a string literal.
The %Q option works like %q except it also adds single quotes around
the outside of the total string. Additionally, if the parameter in the
argument list is a NULL pointer, %Q substitutes the text "NULL" (without
single quotes). So, for example, one could say:
char *zSQL = sqlite3_mprintf("INSERT INTO table VALUES(%Q)", zText);
sqlite3_exec(db, zSQL, 0, 0, 0);
sqlite3_free(zSQL);
The code above will render a correct SQL statement in the zSQL
variable even if the zText variable is a NULL pointer.
The "%z" formatting option works like "%s" but with the
addition that after the string has been read and copied into
the result, sqlite3_free()
is called on the input string.
Mutexes
sqlite3_mutex *sqlite3_mutex_alloc(int);
void sqlite3_mutex_free(sqlite3_mutex*);
void sqlite3_mutex_enter(sqlite3_mutex*);
int sqlite3_mutex_try(sqlite3_mutex*);
void sqlite3_mutex_leave(sqlite3_mutex*);
The SQLite core uses these routines for thread
synchronization. Though they are intended for internal
use by SQLite, code that links against SQLite is
permitted to use any of these routines.
The SQLite source code contains multiple implementations
of these mutex routines. An appropriate implementation
is selected automatically at compile-time. The following
implementations are available in the SQLite core:
- SQLITE_MUTEX_OS2
- SQLITE_MUTEX_PTHREADS
- SQLITE_MUTEX_W32
- SQLITE_MUTEX_NOOP
The SQLITE_MUTEX_NOOP implementation is a set of routines
that does no real locking and is appropriate for use in
a single-threaded application. The SQLITE_MUTEX_OS2,
SQLITE_MUTEX_PTHREADS, and SQLITE_MUTEX_W32 implementations
are appropriate for use on OS/2, Unix, and Windows.
If SQLite is compiled with the SQLITE_MUTEX_APPDEF preprocessor
macro defined (with "-DSQLITE_MUTEX_APPDEF=1"), then no mutex
implementation is included with the library. In this case the
application must supply a custom mutex implementation using the
SQLITE_CONFIG_MUTEX
option of the sqlite3_config() function
before calling sqlite3_initialize() or any other public sqlite3_
function that calls sqlite3_initialize().
The sqlite3_mutex_alloc() routine allocates a new
mutex and returns a pointer to it. If it returns NULL
that means that a mutex could not be allocated. SQLite
will unwind its stack and return an error. The argument
to sqlite3_mutex_alloc() is one of these integer constants:
- SQLITE_MUTEX_FAST
- SQLITE_MUTEX_RECURSIVE
- SQLITE_MUTEX_STATIC_MASTER
- SQLITE_MUTEX_STATIC_MEM
- SQLITE_MUTEX_STATIC_MEM2
- SQLITE_MUTEX_STATIC_PRNG
- SQLITE_MUTEX_STATIC_LRU
- SQLITE_MUTEX_STATIC_LRU2
The first two constants (SQLITE_MUTEX_FAST and SQLITE_MUTEX_RECURSIVE)
cause sqlite3_mutex_alloc() to create
a new mutex. The new mutex is recursive when SQLITE_MUTEX_RECURSIVE
is used but not necessarily so when SQLITE_MUTEX_FAST is used.
The mutex implementation does not need to make a distinction
between SQLITE_MUTEX_RECURSIVE and SQLITE_MUTEX_FAST if it does
not want to. SQLite will only request a recursive mutex in
cases where it really needs one. If a faster non-recursive mutex
implementation is available on the host platform, the mutex subsystem
might return such a mutex in response to SQLITE_MUTEX_FAST.
The other allowed parameters to sqlite3_mutex_alloc() (anything other
than SQLITE_MUTEX_FAST and SQLITE_MUTEX_RECURSIVE) each return
a pointer to a static preexisting mutex. Six static mutexes are
used by the current version of SQLite. Future versions of SQLite
may add additional static mutexes. Static mutexes are for internal
use by SQLite only. Applications that use SQLite mutexes should
use only the dynamic mutexes returned by SQLITE_MUTEX_FAST or
SQLITE_MUTEX_RECURSIVE.
Note that if one of the dynamic mutex parameters (SQLITE_MUTEX_FAST
or SQLITE_MUTEX_RECURSIVE) is used then sqlite3_mutex_alloc()
returns a different mutex on every call. But for the static
mutex types, the same mutex is returned on every call that has
the same type number.
The sqlite3_mutex_free() routine deallocates a previously
allocated dynamic mutex. SQLite is careful to deallocate every
dynamic mutex that it allocates. The dynamic mutexes must not be in
use when they are deallocated. Attempting to deallocate a static
mutex results in undefined behavior. SQLite never deallocates
a static mutex.
The sqlite3_mutex_enter() and sqlite3_mutex_try() routines attempt
to enter a mutex. If another thread is already within the mutex,
sqlite3_mutex_enter() will block and sqlite3_mutex_try() will return
SQLITE_BUSY. The sqlite3_mutex_try() interface returns SQLITE_OK
upon successful entry. Mutexes created using
SQLITE_MUTEX_RECURSIVE can be entered multiple times by the same thread.
In such cases the,
mutex must be exited an equal number of times before another thread
can enter. If the same thread tries to enter any other
kind of mutex more than once, the behavior is undefined.
SQLite will never exhibit
such behavior in its own use of mutexes.
Some systems (for example, Windows 95) do not support the operation
implemented by sqlite3_mutex_try(). On those systems, sqlite3_mutex_try()
will always return SQLITE_BUSY. The SQLite core only ever uses
sqlite3_mutex_try() as an optimization so this is acceptable behavior.
The sqlite3_mutex_leave() routine exits a mutex that was
previously entered by the same thread. The behavior
is undefined if the mutex is not currently entered by the
calling thread or is not currently allocated. SQLite will
never do either.
If the argument to sqlite3_mutex_enter(), sqlite3_mutex_try(), or
sqlite3_mutex_leave() is a NULL pointer, then all three routines
behave as no-ops.
See also: sqlite3_mutex_held()
and sqlite3_mutex_notheld()
.
Mutex Verification Routines
#ifndef NDEBUG
int sqlite3_mutex_held(sqlite3_mutex*);
int sqlite3_mutex_notheld(sqlite3_mutex*);
#endif
The sqlite3_mutex_held() and sqlite3_mutex_notheld() routines
are intended for use inside assert() statements. The SQLite core
never uses these routines except inside an assert() and applications
are advised to follow the lead of the core. The SQLite core only
provides implementations for these routines when it is compiled
with the SQLITE_DEBUG flag. External mutex implementations
are only required to provide these routines if SQLITE_DEBUG is
defined and if NDEBUG is not defined.
These routines should return true if the mutex in their argument
is held or not held, respectively, by the calling thread.
The implementation is not required to provide versions of these
routines that actually work. If the implementation does not provide working
versions of these routines, it should at least provide stubs that always
return true so that one does not get spurious assertion failures.
If the argument to sqlite3_mutex_held() is a NULL pointer then
the routine should return 1. This seems counter-intuitive since
clearly the mutex cannot be held if it does not exist. But
the reason the mutex does not exist is because the build is not
using mutexes. And we do not want the assert() containing the
call to sqlite3_mutex_held() to fail, so a non-zero return is
the appropriate thing to do. The sqlite3_mutex_notheld()
interface should also return 1 when given a NULL pointer.
Opening A New Database Connection
int sqlite3_open(
const char *filename, /* Database filename (UTF-8) */
sqlite3 **ppDb /* OUT: SQLite db handle */
);
int sqlite3_open16(
const void *filename, /* Database filename (UTF-16) */
sqlite3 **ppDb /* OUT: SQLite db handle */
);
int sqlite3_open_v2(
const char *filename, /* Database filename (UTF-8) */
sqlite3 **ppDb, /* OUT: SQLite db handle */
int flags, /* Flags */
const char *zVfs /* Name of VFS module to use */
);
These routines open an SQLite database file as specified by the
filename argument. The filename argument is interpreted as UTF-8 for
sqlite3_open() and sqlite3_open_v2() and as UTF-16 in the native byte
order for sqlite3_open16(). A database connection
handle is usually
returned in *ppDb, even if an error occurs. The only exception is that
if SQLite is unable to allocate memory to hold the sqlite3
object,
a NULL will be written into *ppDb instead of a pointer to the sqlite3
object. If the database is opened (and/or created) successfully, then
SQLITE_OK
is returned. Otherwise an error code
is returned. The
sqlite3_errmsg()
or sqlite3_errmsg16()
routines can be used to obtain
an English language description of the error following a failure of any
of the sqlite3_open() routines.
The default encoding for the database will be UTF-8 if
sqlite3_open() or sqlite3_open_v2() is called and
UTF-16 in the native byte order if sqlite3_open16() is used.
Whether or not an error occurs when it is opened, resources
associated with the database connection
handle should be released by
passing it to sqlite3_close()
when it is no longer required.
The sqlite3_open_v2() interface works like sqlite3_open()
except that it accepts two additional parameters for additional control
over the new database connection. The flags parameter to
sqlite3_open_v2() can take one of
the following three values, optionally combined with the
SQLITE_OPEN_NOMUTEX
, SQLITE_OPEN_FULLMUTEX
, SQLITE_OPEN_SHAREDCACHE
,
SQLITE_OPEN_PRIVATECACHE
, and/or SQLITE_OPEN_URI
flags:
SQLITE_OPEN_READONLY
The database is opened in read-only mode. If the database does not
already exist, an error is returned.
SQLITE_OPEN_READWRITE
The database is opened for reading and writing if possible, or reading
only if the file is write protected by the operating system. In either
case the database must already exist, otherwise an error is returned.
SQLITE_OPEN_READWRITE
| SQLITE_OPEN_CREATE
The database is opened for reading and writing, and is created if
it does not already exist. This is the behavior that is always used for
sqlite3_open() and sqlite3_open16(). If the 3rd parameter to sqlite3_open_v2() is not one of the
combinations shown above optionally combined with other
SQLITE_OPEN_* bits
then the behavior is undefined.
If the SQLITE_OPEN_NOMUTEX
flag is set, then the database connection
opens in the multi-thread threading mode
as long as the single-thread
mode has not been set at compile-time or start-time. If the
SQLITE_OPEN_FULLMUTEX
flag is set then the database connection opens
in the serialized threading mode
unless single-thread was
previously selected at compile-time or start-time.
The SQLITE_OPEN_SHAREDCACHE
flag causes the database connection to be
eligible to use shared cache mode
, regardless of whether or not shared
cache is enabled using sqlite3_enable_shared_cache()
. The
SQLITE_OPEN_PRIVATECACHE
flag causes the database connection to not
participate in shared cache mode
even if it is enabled.
The fourth parameter to sqlite3_open_v2() is the name of the
sqlite3_vfs
object that defines the operating system interface that
the new database connection should use. If the fourth parameter is
a NULL pointer then the default sqlite3_vfs
object is used.
If the filename is ":memory:", then a private, temporary in-memory database
is created for the connection. This in-memory database will vanish when
the database connection is closed. Future versions of SQLite might
make use of additional special filenames that begin with the ":" character.
It is recommended that when a database filename actually does begin with
a ":" character you should prefix the filename with a pathname such as
"./" to avoid ambiguity.
If the filename is an empty string, then a private, temporary
on-disk database will be created. This private database will be
automatically deleted as soon as the database connection is closed.
URI Filenames
If URI filename
interpretation is enabled, and the filename argument
begins with "file:", then the filename is interpreted as a URI. URI
filename interpretation is enabled if the SQLITE_OPEN_URI
flag is
set in the fourth argument to sqlite3_open_v2(), or if it has
been enabled globally using the SQLITE_CONFIG_URI
option with the
sqlite3_config()
method or by the SQLITE_USE_URI
compile-time option.
As of SQLite version 3.7.7, URI filename interpretation is turned off
by default, but future releases of SQLite might enable URI filename
interpretation by default. See "URI filenames
" for additional
information.
URI filenames are parsed according to RFC 3986. If the URI contains an
authority, then it must be either an empty string or the string
"localhost". If the authority is not an empty string or "localhost", an
error is returned to the caller. The fragment component of a URI, if
present, is ignored.
SQLite uses the path component of the URI as the name of the disk file
which contains the database. If the path begins with a '/' character,
then it is interpreted as an absolute path. If the path does not begin
with a '/' (meaning that the authority section is omitted from the URI)
then the path is interpreted as a relative path.
On windows, the first component of an absolute path
is a drive specification (e.g. "C:").
The query component of a URI may contain parameters that are interpreted
either by SQLite itself, or by a custom VFS implementation
.
SQLite interprets the following three query parameters:
- vfs
: The "vfs" parameter may be used to specify the name of
a VFS object that provides the operating system interface that should
be used to access the database file on disk. If this option is set to
an empty string the default VFS object is used. Specifying an unknown
VFS is an error. If sqlite3_open_v2() is used and the vfs option is
present, then the VFS specified by the option takes precedence over
the value passed as the fourth parameter to sqlite3_open_v2().
- mode
: The mode parameter may be set to either "ro", "rw" or
"rwc". Attempting to set it to any other value is an error.
If "ro" is specified, then the database is opened for read-only
access, just as if the SQLITE_OPEN_READONLY
flag had been set in the
third argument to sqlite3_prepare_v2(). If the mode option is set to
"rw", then the database is opened for read-write (but not create)
access, as if SQLITE_OPEN_READWRITE (but not SQLITE_OPEN_CREATE) had
been set. Value "rwc" is equivalent to setting both
SQLITE_OPEN_READWRITE and SQLITE_OPEN_CREATE. If sqlite3_open_v2() is
used, it is an error to specify a value for the mode parameter that is
less restrictive than that specified by the flags passed as the third
parameter.
- cache
: The cache parameter may be set to either "shared" or
"private". Setting it to "shared" is equivalent to setting the
SQLITE_OPEN_SHAREDCACHE bit in the flags argument passed to
sqlite3_open_v2(). Setting the cache parameter to "private" is
equivalent to setting the SQLITE_OPEN_PRIVATECACHE bit.
If sqlite3_open_v2() is used and the "cache" parameter is present in
a URI filename, its value overrides any behaviour requested by setting
SQLITE_OPEN_PRIVATECACHE or SQLITE_OPEN_SHAREDCACHE flag.
Specifying an unknown parameter in the query component of a URI is not an
error. Future versions of SQLite might understand additional query
parameters. See "query parameters with special meaning to SQLite
" for
additional information.
URI filename examples
URI filenames
Results
file:data.db
Open the file "data.db" in the current directory.
file:/home/fred/data.db
file:///home/fred/data.db
file://localhost/home/fred/data.db
Open the database file "/home/fred/data.db".
file://darkstar/home/fred/data.db
An error. "darkstar" is not a recognized authority.
file:///C:/Documents%20and%20Settings/fred/Desktop/data.db
Windows only: Open the file "data.db" on fred's desktop on drive
C:. Note that the %20 escaping in this example is not strictly
necessary - space characters can be used literally
in URI filenames.
file:data.db?mode=ro&cache=private
Open file "data.db" in the current directory for read-only access.
Regardless of whether or not shared-cache mode is enabled by
default, use a private cache.
file:/home/fred/data.db?vfs=unix-nolock
Open file "/home/fred/data.db". Use the special VFS "unix-nolock".
file:data.db?mode=readonly
An error. "readonly" is not a valid option for the "mode" parameter.
URI hexadecimal escape sequences (%HH) are supported within the path and
query components of a URI. A hexadecimal escape sequence consists of a
percent sign - "%" - followed by exactly two hexadecimal digits
specifying an octet value. Before the path or query components of a
URI filename are interpreted, they are encoded using UTF-8 and all
hexadecimal escape sequences replaced by a single byte containing the
corresponding octet. If this process generates an invalid UTF-8 encoding,
the results are undefined.
Note to Windows users:
The encoding used for the filename argument
of sqlite3_open() and sqlite3_open_v2() must be UTF-8, not whatever
codepage is currently defined. Filenames containing international
characters must be converted to UTF-8 prior to passing them into
sqlite3_open() or sqlite3_open_v2().
Tracing And Profiling Functions
void *sqlite3_trace(sqlite3*, void(*xTrace)(void*,const char*), void*);
void *sqlite3_profile(sqlite3*,
void(*xProfile)(void*,const char*,sqlite3_uint64), void*);
These routines register callback functions that can be used for
tracing and profiling the execution of SQL statements.
The callback function registered by sqlite3_trace() is invoked at
various times when an SQL statement is being run by sqlite3_step()
.
The sqlite3_trace() callback is invoked with a UTF-8 rendering of the
SQL statement text as the statement first begins executing.
Additional sqlite3_trace() callbacks might occur
as each triggered subprogram is entered. The callbacks for triggers
contain a UTF-8 SQL comment that identifies the trigger.
The callback function registered by sqlite3_profile() is invoked
as each SQL statement finishes. The profile callback contains
the original statement text and an estimate of wall-clock time
of how long that statement took to run. The profile callback
time is in units of nanoseconds, however the current implementation
is only capable of millisecond resolution so the six least significant
digits in the time are meaningless. Future versions of SQLite
might provide greater resolution on the profiler callback. The
sqlite3_profile() function is considered experimental and is
subject to change in future versions of SQLite.
Setting The Result Of An SQL Function
void sqlite3_result_blob(sqlite3_context*, const void*, int, void(*)(void*));
void sqlite3_result_double(sqlite3_context*, double);
void sqlite3_result_error(sqlite3_context*, const char*, int);
void sqlite3_result_error16(sqlite3_context*, const void*, int);
void sqlite3_result_error_toobig(sqlite3_context*);
void sqlite3_result_error_nomem(sqlite3_context*);
void sqlite3_result_error_code(sqlite3_context*, int);
void sqlite3_result_int(sqlite3_context*, int);
void sqlite3_result_int64(sqlite3_context*, sqlite3_int64);
void sqlite3_result_null(sqlite3_context*);
void sqlite3_result_text(sqlite3_context*, const char*, int, void(*)(void*));
void sqlite3_result_text16(sqlite3_context*, const void*, int, void(*)(void*));
void sqlite3_result_text16le(sqlite3_context*, const void*, int,void(*)(void*));
void sqlite3_result_text16be(sqlite3_context*, const void*, int,void(*)(void*));
void sqlite3_result_value(sqlite3_context*, sqlite3_value*);
void sqlite3_result_zeroblob(sqlite3_context*, int n);
These routines are used by the xFunc or xFinal callbacks that
implement SQL functions and aggregates. See
sqlite3_create_function()
and sqlite3_create_function16()
for additional information.
These functions work very much like the parameter binding
family of
functions used to bind values to host parameters in prepared statements.
Refer to the SQL parameter
documentation for additional information.
The sqlite3_result_blob() interface sets the result from
an application-defined function to be the BLOB whose content is pointed
to by the second parameter and which is N bytes long where N is the
third parameter.
The sqlite3_result_zeroblob() interfaces set the result of
the application-defined function to be a BLOB containing all zero
bytes and N bytes in size, where N is the value of the 2nd parameter.
The sqlite3_result_double() interface sets the result from
an application-defined function to be a floating point value specified
by its 2nd argument.
The sqlite3_result_error() and sqlite3_result_error16() functions
cause the implemented SQL function to throw an exception.
SQLite uses the string pointed to by the
2nd parameter of sqlite3_result_error() or sqlite3_result_error16()
as the text of an error message. SQLite interprets the error
message string from sqlite3_result_error() as UTF-8. SQLite
interprets the string from sqlite3_result_error16() as UTF-16 in native
byte order. If the third parameter to sqlite3_result_error()
or sqlite3_result_error16() is negative then SQLite takes as the error
message all text up through the first zero character.
If the third parameter to sqlite3_result_error() or
sqlite3_result_error16() is non-negative then SQLite takes that many
bytes (not characters) from the 2nd parameter as the error message.
The sqlite3_result_error() and sqlite3_result_error16()
routines make a private copy of the error message text before
they return. Hence, the calling function can deallocate or
modify the text after they return without harm.
The sqlite3_result_error_code() function changes the error code
returned by SQLite as a result of an error in a function. By default,
the error code is SQLITE_ERROR. A subsequent call to sqlite3_result_error()
or sqlite3_result_error16() resets the error code to SQLITE_ERROR.
The sqlite3_result_toobig() interface causes SQLite to throw an error
indicating that a string or BLOB is too long to represent.
The sqlite3_result_nomem() interface causes SQLite to throw an error
indicating that a memory allocation failed.
The sqlite3_result_int() interface sets the return value
of the application-defined function to be the 32-bit signed integer
value given in the 2nd argument.
The sqlite3_result_int64() interface sets the return value
of the application-defined function to be the 64-bit signed integer
value given in the 2nd argument.
The sqlite3_result_null() interface sets the return value
of the application-defined function to be NULL.
The sqlite3_result_text(), sqlite3_result_text16(),
sqlite3_result_text16le(), and sqlite3_result_text16be() interfaces
set the return value of the application-defined function to be
a text string which is represented as UTF-8, UTF-16 native byte order,
UTF-16 little endian, or UTF-16 big endian, respectively.
SQLite takes the text result from the application from
the 2nd parameter of the sqlite3_result_text* interfaces.
If the 3rd parameter to the sqlite3_result_text* interfaces
is negative, then SQLite takes result text from the 2nd parameter
through the first zero character.
If the 3rd parameter to the sqlite3_result_text* interfaces
is non-negative, then as many bytes (not characters) of the text
pointed to by the 2nd parameter are taken as the application-defined
function result. If the 3rd parameter is non-negative, then it
must be the byte offset into the string where the NUL terminator would
appear if the string where NUL terminated. If any NUL characters occur
in the string at a byte offset that is less than the value of the 3rd
parameter, then the resulting string will contain embedded NULs and the
result of expressions operating on strings with embedded NULs is undefined.
If the 4th parameter to the sqlite3_result_text* interfaces
or sqlite3_result_blob is a non-NULL pointer, then SQLite calls that
function as the destructor on the text or BLOB result when it has
finished using that result.
If the 4th parameter to the sqlite3_result_text* interfaces or to
sqlite3_result_blob is the special constant SQLITE_STATIC, then SQLite
assumes that the text or BLOB result is in constant space and does not
copy the content of the parameter nor call a destructor on the content
when it has finished using that result.
If the 4th parameter to the sqlite3_result_text* interfaces
or sqlite3_result_blob is the special constant SQLITE_TRANSIENT
then SQLite makes a copy of the result into space obtained from
from sqlite3_malloc()
before it returns.
The sqlite3_result_value() interface sets the result of
the application-defined function to be a copy the
unprotected sqlite3_value
object specified by the 2nd parameter. The
sqlite3_result_value() interface makes a copy of the sqlite3_value
so that the sqlite3_value
specified in the parameter may change or
be deallocated after sqlite3_result_value() returns without harm.
A protected sqlite3_value
object may always be used where an
unprotected sqlite3_value
object is required, so either
kind of sqlite3_value
object can be used with this interface.
If these routines are called from within the different thread
than the one containing the application-defined function that received
the sqlite3_context
pointer, the results are undefined.
Obtain Values For URI Parameters
const char *sqlite3_uri_parameter(const char *zFilename, const char *zParam);
int sqlite3_uri_boolean(const char *zFile, const char *zParam, int bDefault);
sqlite3_int64 sqlite3_uri_int64(const char*, const char*, sqlite3_int64);
These are utility routines, useful to VFS implementations, that check
to see if a database file was a URI that contained a specific query
parameter, and if so obtains the value of that query parameter.
If F is the database filename pointer passed into the xOpen() method of
a VFS implementation when the flags parameter to xOpen() has one or
more of the SQLITE_OPEN_URI
or SQLITE_OPEN_MAIN_DB
bits set and
P is the name of the query parameter, then
sqlite3_uri_parameter(F,P) returns the value of the P
parameter if it exists or a NULL pointer if P does not appear as a
query parameter on F. If P is a query parameter of F
has no explicit value, then sqlite3_uri_parameter(F,P) returns
a pointer to an empty string.
The sqlite3_uri_boolean(F,P,B) routine assumes that P is a boolean
parameter and returns true (1) or false (0) according to the value
of P. The value of P is true if it is "yes" or "true" or "on" or
a non-zero number and is false otherwise. If P is not a query parameter
on F then sqlite3_uri_boolean(F,P,B) returns (B!=0).
The sqlite3_uri_int64(F,P,D) routine converts the value of P into a
64-bit signed integer and returns that integer, or D if P does not
exist. If the value of P is something other than an integer, then
zero is returned.
If F is a NULL pointer, then sqlite3_uri_parameter(F,P) returns NULL and
sqlite3_uri_boolean(F,P,B) returns B. If F is not a NULL pointer and
is not a database file pathname pointer that SQLite passed into the xOpen
VFS method, then the behavior of this routine is undefined and probably
undesirable.
Obtaining SQL Function Parameter Values
const void *sqlite3_value_blob(sqlite3_value*);
int sqlite3_value_bytes(sqlite3_value*);
int sqlite3_value_bytes16(sqlite3_value*);
double sqlite3_value_double(sqlite3_value*);
int sqlite3_value_int(sqlite3_value*);
sqlite3_int64 sqlite3_value_int64(sqlite3_value*);
const unsigned char *sqlite3_value_text(sqlite3_value*);
const void *sqlite3_value_text16(sqlite3_value*);
const void *sqlite3_value_text16le(sqlite3_value*);
const void *sqlite3_value_text16be(sqlite3_value*);
int sqlite3_value_type(sqlite3_value*);
int sqlite3_value_numeric_type(sqlite3_value*);
The C-language implementation of SQL functions and aggregates uses
this set of interface routines to access the parameter values on
the function or aggregate.
The xFunc (for scalar functions) or xStep (for aggregates) parameters
to sqlite3_create_function()
and sqlite3_create_function16()
define callbacks that implement the SQL functions and aggregates.
The 3rd parameter to these callbacks is an array of pointers to
protected sqlite3_value
objects. There is one sqlite3_value
object for
each parameter to the SQL function. These routines are used to
extract values from the sqlite3_value
objects.
These routines work only with protected sqlite3_value
objects.
Any attempt to use these routines on an unprotected sqlite3_value
object results in undefined behavior.
These routines work just like the corresponding column access functions
except that these routines take a single protected sqlite3_value
object
pointer instead of a sqlite3_stmt*
pointer and an integer column number.
The sqlite3_value_text16() interface extracts a UTF-16 string
in the native byte-order of the host machine. The
sqlite3_value_text16be() and sqlite3_value_text16le() interfaces
extract UTF-16 strings as big-endian and little-endian respectively.
The sqlite3_value_numeric_type() interface attempts to apply
numeric affinity to the value. This means that an attempt is
made to convert the value to an integer or floating point. If
such a conversion is possible without loss of information (in other
words, if the value is a string that looks like a number)
then the conversion is performed. Otherwise no conversion occurs.
The datatype
after conversion is returned.
Please pay particular attention to the fact that the pointer returned
from sqlite3_value_blob()
, sqlite3_value_text()
, or
sqlite3_value_text16()
can be invalidated by a subsequent call to
sqlite3_value_bytes()
, sqlite3_value_bytes16()
, sqlite3_value_text()
,
or sqlite3_value_text16()
.
These routines must be called from the same thread as
the SQL function that supplied the sqlite3_value*
parameters.
Virtual File System Objects
sqlite3_vfs *sqlite3_vfs_find(const char *zVfsName);
int sqlite3_vfs_register(sqlite3_vfs*, int makeDflt);
int sqlite3_vfs_unregister(sqlite3_vfs*);
A virtual filesystem (VFS) is an sqlite3_vfs
object
that SQLite uses to interact
with the underlying operating system. Most SQLite builds come with a
single default VFS that is appropriate for the host computer.
New VFSes can be registered and existing VFSes can be unregistered.
The following interfaces are provided.
The sqlite3_vfs_find() interface returns a pointer to a VFS given its name.
Names are case sensitive.
Names are zero-terminated UTF-8 strings.
If there is no match, a NULL pointer is returned.
If zVfsName is NULL then the default VFS is returned.
New VFSes are registered with sqlite3_vfs_register().
Each new VFS becomes the default VFS if the makeDflt flag is set.
The same VFS can be registered multiple times without injury.
To make an existing VFS into the default VFS, register it again
with the makeDflt flag set. If two different VFSes with the
same name are registered, the behavior is undefined. If a
VFS is registered with a name that is NULL or an empty string,
then the behavior is undefined.
Unregister a VFS with the sqlite3_vfs_unregister() interface.
If the default VFS is unregistered, another VFS is chosen as
the default. The choice for the new VFS is arbitrary.
Binding Values To Prepared Statements
int sqlite3_bind_blob(sqlite3_stmt*, int, const void*, int n, void(*)(void*));
int sqlite3_bind_double(sqlite3_stmt*, int, double);
int sqlite3_bind_int(sqlite3_stmt*, int, int);
int sqlite3_bind_int64(sqlite3_stmt*, int, sqlite3_int64);
int sqlite3_bind_null(sqlite3_stmt*, int);
int sqlite3_bind_text(sqlite3_stmt*, int, const char*, int n, void(*)(void*));
int sqlite3_bind_text16(sqlite3_stmt*, int, const void*, int, void(*)(void*));
int sqlite3_bind_value(sqlite3_stmt*, int, const sqlite3_value*);
int sqlite3_bind_zeroblob(sqlite3_stmt*, int, int n);
In the SQL statement text input to sqlite3_prepare_v2()
and its variants,
literals may be replaced by a parameter
that matches one of following
templates:
In the templates above, NNN represents an integer literal,
and VVV represents an alphanumeric identifier. The values of these
parameters (also called "host parameter names" or "SQL parameters")
can be set using the sqlite3_bind_*() routines defined here.
The first argument to the sqlite3_bind_*() routines is always
a pointer to the sqlite3_stmt
object returned from
sqlite3_prepare_v2()
or its variants.
The second argument is the index of the SQL parameter to be set.
The leftmost SQL parameter has an index of 1. When the same named
SQL parameter is used more than once, second and subsequent
occurrences have the same index as the first occurrence.
The index for named parameters can be looked up using the
sqlite3_bind_parameter_index()
API if desired. The index
for "?NNN" parameters is the value of NNN.
The NNN value must be between 1 and the sqlite3_limit()
parameter SQLITE_LIMIT_VARIABLE_NUMBER
(default value: 999).
The third argument is the value to bind to the parameter.
In those routines that have a fourth argument, its value is the
number of bytes in the parameter. To be clear: the value is the
number of bytes
in the value, not the number of characters.
If the fourth parameter is negative, the length of the string is
the number of bytes up to the first zero terminator.
If a non-negative fourth parameter is provided to sqlite3_bind_text()
or sqlite3_bind_text16() then that parameter must be the byte offset
where the NUL terminator would occur assuming the string were NUL
terminated. If any NUL characters occur at byte offsets less than
the value of the fourth parameter then the resulting string value will
contain embedded NULs. The result of expressions involving strings
with embedded NULs is undefined.
The fifth argument to sqlite3_bind_blob(), sqlite3_bind_text(), and
sqlite3_bind_text16() is a destructor used to dispose of the BLOB or
string after SQLite has finished with it. The destructor is called
to dispose of the BLOB or string even if the call to sqlite3_bind_blob(),
sqlite3_bind_text(), or sqlite3_bind_text16() fails.
If the fifth argument is
the special value SQLITE_STATIC
, then SQLite assumes that the
information is in static, unmanaged space and does not need to be freed.
If the fifth argument has the value SQLITE_TRANSIENT
, then
SQLite makes its own private copy of the data immediately, before
the sqlite3_bind_*() routine returns.
The sqlite3_bind_zeroblob() routine binds a BLOB of length N that
is filled with zeroes. A zeroblob uses a fixed amount of memory
(just an integer to hold its size) while it is being processed.
Zeroblobs are intended to serve as placeholders for BLOBs whose
content is later written using
incremental BLOB I/O
routines.
A negative value for the zeroblob results in a zero-length BLOB.
If any of the sqlite3_bind_*() routines are called with a NULL pointer
for the prepared statement
or with a prepared statement for which
sqlite3_step()
has been called more recently than sqlite3_reset()
,
then the call will return SQLITE_MISUSE
. If any sqlite3_bind_()
routine is passed a prepared statement
that has been finalized, the
result is undefined and probably harmful.
Bindings are not cleared by the sqlite3_reset()
routine.
Unbound parameters are interpreted as NULL.
The sqlite3_bind_* routines return SQLITE_OK
on success or an
error code
if anything goes wrong.
SQLITE_RANGE
is returned if the parameter
index is out of range. SQLITE_NOMEM
is returned if malloc() fails.
See also: sqlite3_bind_parameter_count()
,
sqlite3_bind_parameter_name()
, and sqlite3_bind_parameter_index()
.
Compiling An SQL Statement
int sqlite3_prepare(
sqlite3 *db, /* Database handle */
const char *zSql, /* SQL statement, UTF-8 encoded */
int nByte, /* Maximum length of zSql in bytes. */
sqlite3_stmt **ppStmt, /* OUT: Statement handle */
const char **pzTail /* OUT: Pointer to unused portion of zSql */
);
int sqlite3_prepare_v2(
sqlite3 *db, /* Database handle */
const char *zSql, /* SQL statement, UTF-8 encoded */
int nByte, /* Maximum length of zSql in bytes. */
sqlite3_stmt **ppStmt, /* OUT: Statement handle */
const char **pzTail /* OUT: Pointer to unused portion of zSql */
);
int sqlite3_prepare16(
sqlite3 *db, /* Database handle */
const void *zSql, /* SQL statement, UTF-16 encoded */
int nByte, /* Maximum length of zSql in bytes. */
sqlite3_stmt **ppStmt, /* OUT: Statement handle */
const void **pzTail /* OUT: Pointer to unused portion of zSql */
);
int sqlite3_prepare16_v2(
sqlite3 *db, /* Database handle */
const void *zSql, /* SQL statement, UTF-16 encoded */
int nByte, /* Maximum length of zSql in bytes. */
sqlite3_stmt **ppStmt, /* OUT: Statement handle */
const void **pzTail /* OUT: Pointer to unused portion of zSql */
);
To execute an SQL query, it must first be compiled into a byte-code
program using one of these routines.
The first argument, "db", is a database connection
obtained from a
prior successful call to sqlite3_open()
, sqlite3_open_v2()
or
sqlite3_open16()
. The database connection must not have been closed.
The second argument, "zSql", is the statement to be compiled, encoded
as either UTF-8 or UTF-16. The sqlite3_prepare() and sqlite3_prepare_v2()
interfaces use UTF-8, and sqlite3_prepare16() and sqlite3_prepare16_v2()
use UTF-16.
If the nByte argument is less than zero, then zSql is read up to the
first zero terminator. If nByte is non-negative, then it is the maximum
number of bytes read from zSql. When nByte is non-negative, the
zSql string ends at either the first '\000' or '\u0000' character or
the nByte-th byte, whichever comes first. If the caller knows
that the supplied string is nul-terminated, then there is a small
performance advantage to be gained by passing an nByte parameter that
is equal to the number of bytes in the input string including
the nul-terminator bytes as this saves SQLite from having to
make a copy of the input string.
If pzTail is not NULL then *pzTail is made to point to the first byte
past the end of the first SQL statement in zSql. These routines only
compile the first statement in zSql, so *pzTail is left pointing to
what remains uncompiled.
*ppStmt is left pointing to a compiled prepared statement
that can be
executed using sqlite3_step()
. If there is an error, *ppStmt is set
to NULL. If the input text contains no SQL (if the input is an empty
string or a comment) then *ppStmt is set to NULL.
The calling procedure is responsible for deleting the compiled
SQL statement using sqlite3_finalize()
after it has finished with it.
ppStmt may not be NULL.
On success, the sqlite3_prepare() family of routines return SQLITE_OK
;
otherwise an error code
is returned.
The sqlite3_prepare_v2() and sqlite3_prepare16_v2() interfaces are
recommended for all new programs. The two older interfaces are retained
for backwards compatibility, but their use is discouraged.
In the "v2" interfaces, the prepared statement
that is returned (the sqlite3_stmt
object) contains a copy of the
original SQL text. This causes the sqlite3_step()
interface to
behave differently in three ways:
If the database schema changes, instead of returning SQLITE_SCHEMA
as it
always used to do, sqlite3_step()
will automatically recompile the SQL
statement and try to run it again.
When an error occurs, sqlite3_step()
will return one of the detailed
error codes
or extended error codes
. The legacy behavior was that
sqlite3_step()
would only return a generic SQLITE_ERROR
result code
and the application would have to make a second call to sqlite3_reset()
in order to find the underlying cause of the problem. With the "v2" prepare
interfaces, the underlying reason for the error is returned immediately.
If the specific value bound to host parameter
in the
WHERE clause might influence the choice of query plan for a statement,
then the statement will be automatically recompiled, as if there had been
a schema change, on the first sqlite3_step()
call following any change
to the bindings
of that parameter
.
The specific value of WHERE-clause parameter
might influence the
choice of query plan if the parameter is the left-hand side of a LIKE
or GLOB
operator or if the parameter is compared to an indexed column
and the SQLITE_ENABLE_STAT3
compile-time option is enabled.
the
Create Or Redefine SQL Functions
int sqlite3_create_function(
sqlite3 *db,
const char *zFunctionName,
int nArg,
int eTextRep,
void *pApp,
void (*xFunc)(sqlite3_context*,int,sqlite3_value**),
void (*xStep)(sqlite3_context*,int,sqlite3_value**),
void (*xFinal)(sqlite3_context*)
);
int sqlite3_create_function16(
sqlite3 *db,
const void *zFunctionName,
int nArg,
int eTextRep,
void *pApp,
void (*xFunc)(sqlite3_context*,int,sqlite3_value**),
void (*xStep)(sqlite3_context*,int,sqlite3_value**),
void (*xFinal)(sqlite3_context*)
);
int sqlite3_create_function_v2(
sqlite3 *db,
const char *zFunctionName,
int nArg,
int eTextRep,
void *pApp,
void (*xFunc)(sqlite3_context*,int,sqlite3_value**),
void (*xStep)(sqlite3_context*,int,sqlite3_value**),
void (*xFinal)(sqlite3_context*),
void(*xDestroy)(void*)
);
These functions (collectively known as "function creation routines")
are used to add SQL functions or aggregates or to redefine the behavior
of existing SQL functions or aggregates. The only differences between
these routines are the text encoding expected for
the second parameter (the name of the function being created)
and the presence or absence of a destructor callback for
the application data pointer.
The first parameter is the database connection
to which the SQL
function is to be added. If an application uses more than one database
connection then application-defined SQL functions must be added
to each database connection separately.
The second parameter is the name of the SQL function to be created or
redefined. The length of the name is limited to 255 bytes in a UTF-8
representation, exclusive of the zero-terminator. Note that the name
length limit is in UTF-8 bytes, not characters nor UTF-16 bytes.
Any attempt to create a function with a longer name
will result in SQLITE_MISUSE
being returned.
The third parameter (nArg)
is the number of arguments that the SQL function or
aggregate takes. If this parameter is -1, then the SQL function or
aggregate may take any number of arguments between 0 and the limit
set by sqlite3_limit
(SQLITE_LIMIT_FUNCTION_ARG
). If the third
parameter is less than -1 or greater than 127 then the behavior is
undefined.
The fourth parameter, eTextRep, specifies what
text encoding
this SQL function prefers for
its parameters. Every SQL function implementation must be able to work
with UTF-8, UTF-16le, or UTF-16be. But some implementations may be
more efficient with one encoding than another. An application may
invoke sqlite3_create_function() or sqlite3_create_function16() multiple
times with the same function but with different values of eTextRep.
When multiple implementations of the same function are available, SQLite
will pick the one that involves the least amount of data conversion.
If there is only a single implementation which does not care what text
encoding is used, then the fourth argument should be SQLITE_ANY
.
The fifth parameter is an arbitrary pointer. The implementation of the
function can gain access to this pointer using sqlite3_user_data()
.
The sixth, seventh and eighth parameters, xFunc, xStep and xFinal, are
pointers to C-language functions that implement the SQL function or
aggregate. A scalar SQL function requires an implementation of the xFunc
callback only; NULL pointers must be passed as the xStep and xFinal
parameters. An aggregate SQL function requires an implementation of xStep
and xFinal and NULL pointer must be passed for xFunc. To delete an existing
SQL function or aggregate, pass NULL pointers for all three function
callbacks.
If the ninth parameter to sqlite3_create_function_v2() is not NULL,
then it is destructor for the application data pointer.
The destructor is invoked when the function is deleted, either by being
overloaded or when the database connection closes.
The destructor is also invoked if the call to
sqlite3_create_function_v2() fails.
When the destructor callback of the tenth parameter is invoked, it
is passed a single argument which is a copy of the application data
pointer which was the fifth parameter to sqlite3_create_function_v2().
It is permitted to register multiple implementations of the same
functions with the same name but with either differing numbers of
arguments or differing preferred text encodings. SQLite will use
the implementation that most closely matches the way in which the
SQL function is used. A function implementation with a non-negative
nArg parameter is a better match than a function implementation with
a negative nArg. A function where the preferred text encoding
matches the database encoding is a better
match than a function where the encoding is different.
A function where the encoding difference is between UTF16le and UTF16be
is a closer match than a function where the encoding difference is
between UTF8 and UTF16.
Built-in functions may be overloaded by new application-defined functions.
An application-defined function is permitted to call other
SQLite interfaces. However, such calls must not
close the database connection nor finalize or reset the prepared
statement in which the function is running.
Test For Auto-Commit Mode
int sqlite3_get_autocommit(sqlite3*);
The sqlite3_get_autocommit() interface returns non-zero or
zero if the given database connection is or is not in autocommit mode,
respectively. Autocommit mode is on by default.
Autocommit mode is disabled by a BEGIN
statement.
Autocommit mode is re-enabled by a COMMIT
or ROLLBACK
.
If certain kinds of errors occur on a statement within a multi-statement
transaction (errors including SQLITE_FULL
, SQLITE_IOERR
,
SQLITE_NOMEM
, SQLITE_BUSY
, and SQLITE_INTERRUPT
) then the
transaction might be rolled back automatically. The only way to
find out whether SQLite automatically rolled back the transaction after
an error is to use this function.
If another thread changes the autocommit status of the database
connection while this routine is running, then the return value
is undefined.
Result Values From A Query
const void *sqlite3_column_blob(sqlite3_stmt*, int iCol);
int sqlite3_column_bytes(sqlite3_stmt*, int iCol);
int sqlite3_column_bytes16(sqlite3_stmt*, int iCol);
double sqlite3_column_double(sqlite3_stmt*, int iCol);
int sqlite3_column_int(sqlite3_stmt*, int iCol);
sqlite3_int64 sqlite3_column_int64(sqlite3_stmt*, int iCol);
const unsigned char *sqlite3_column_text(sqlite3_stmt*, int iCol);
const void *sqlite3_column_text16(sqlite3_stmt*, int iCol);
int sqlite3_column_type(sqlite3_stmt*, int iCol);
sqlite3_value *sqlite3_column_value(sqlite3_stmt*, int iCol);
These routines form the "result set" interface.
These routines return information about a single column of the current
result row of a query. In every case the first argument is a pointer
to the prepared statement
that is being evaluated (the sqlite3_stmt*
that was returned from sqlite3_prepare_v2()
or one of its variants)
and the second argument is the index of the column for which information
should be returned. The leftmost column of the result set has the index 0.
The number of columns in the result can be determined using
sqlite3_column_count()
.
If the SQL statement does not currently point to a valid row, or if the
column index is out of range, the result is undefined.
These routines may only be called when the most recent call to
sqlite3_step()
has returned SQLITE_ROW
and neither
sqlite3_reset()
nor sqlite3_finalize()
have been called subsequently.
If any of these routines are called after sqlite3_reset()
or
sqlite3_finalize()
or after sqlite3_step()
has returned
something other than SQLITE_ROW
, the results are undefined.
If sqlite3_step()
or sqlite3_reset()
or sqlite3_finalize()
are called from a different thread while any of these routines
are pending, then the results are undefined.
The sqlite3_column_type() routine returns the
datatype code
for the initial data type
of the result column. The returned value is one of SQLITE_INTEGER
,
SQLITE_FLOAT
, SQLITE_TEXT
, SQLITE_BLOB
, or SQLITE_NULL
. The value
returned by sqlite3_column_type() is only meaningful if no type
conversions have occurred as described below. After a type conversion,
the value returned by sqlite3_column_type() is undefined. Future
versions of SQLite may change the behavior of sqlite3_column_type()
following a type conversion.
If the result is a BLOB or UTF-8 string then the sqlite3_column_bytes()
routine returns the number of bytes in that BLOB or string.
If the result is a UTF-16 string, then sqlite3_column_bytes() converts
the string to UTF-8 and then returns the number of bytes.
If the result is a numeric value then sqlite3_column_bytes() uses
sqlite3_snprintf()
to convert that value to a UTF-8 string and returns
the number of bytes in that string.
If the result is NULL, then sqlite3_column_bytes() returns zero.
If the result is a BLOB or UTF-16 string then the sqlite3_column_bytes16()
routine returns the number of bytes in that BLOB or string.
If the result is a UTF-8 string, then sqlite3_column_bytes16() converts
the string to UTF-16 and then returns the number of bytes.
If the result is a numeric value then sqlite3_column_bytes16() uses
sqlite3_snprintf()
to convert that value to a UTF-16 string and returns
the number of bytes in that string.
If the result is NULL, then sqlite3_column_bytes16() returns zero.
The values returned by sqlite3_column_bytes()
and
sqlite3_column_bytes16()
do not include the zero terminators at the end
of the string. For clarity: the values returned by
sqlite3_column_bytes()
and sqlite3_column_bytes16()
are the number of
bytes in the string, not the number of characters.
Strings returned by sqlite3_column_text() and sqlite3_column_text16(),
even empty strings, are always zero-terminated. The return
value from sqlite3_column_blob() for a zero-length BLOB is a NULL pointer.
The object returned by sqlite3_column_value()
is an
unprotected sqlite3_value
object. An unprotected sqlite3_value object
may only be used with sqlite3_bind_value()
and sqlite3_result_value()
.
If the unprotected sqlite3_value
object returned by
sqlite3_column_value()
is used in any other way, including calls
to routines like sqlite3_value_int()
, sqlite3_value_text()
,
or sqlite3_value_bytes()
, then the behavior is undefined.
These routines attempt to convert the value where appropriate. For
example, if the internal representation is FLOAT and a text result
is requested, sqlite3_snprintf()
is used internally to perform the
conversion automatically. The following table details the conversions
that are applied:
Internal
Type
Requested
Type
Conversion
NULL
INTEGER
Result is 0
NULL
FLOAT
Result is 0.0
NULL
TEXT
Result is NULL pointer
NULL
BLOB
Result is NULL pointer
INTEGER
FLOAT
Convert from integer to float
INTEGER
TEXT
ASCII rendering of the integer
INTEGER
BLOB
Same as INTEGER->TEXT
FLOAT
INTEGER
Convert from float to integer
FLOAT
TEXT
ASCII rendering of the float
FLOAT
BLOB
Same as FLOAT->TEXT
TEXT
INTEGER
Use atoi()
TEXT
FLOAT
Use atof()
TEXT
BLOB
No change
BLOB
INTEGER
Convert to TEXT then use atoi()
BLOB
FLOAT
Convert to TEXT then use atof()
BLOB
TEXT
Add a zero terminator if needed
The table above makes reference to standard C library functions atoi()
and atof(). SQLite does not really use these functions. It has its
own equivalent internal routines. The atoi() and atof() names are
used in the table for brevity and because they are familiar to most
C programmers.
Note that when type conversions occur, pointers returned by prior
calls to sqlite3_column_blob(), sqlite3_column_text(), and/or
sqlite3_column_text16() may be invalidated.
Type conversions and pointer invalidations might occur
in the following cases:
- The initial content is a BLOB and sqlite3_column_text() or
sqlite3_column_text16() is called. A zero-terminator might
need to be added to the string.
- The initial content is UTF-8 text and sqlite3_column_bytes16() or
sqlite3_column_text16() is called. The content must be converted
to UTF-16.
- The initial content is UTF-16 text and sqlite3_column_bytes() or
sqlite3_column_text() is called. The content must be converted
to UTF-8.
Conversions between UTF-16be and UTF-16le are always done in place and do
not invalidate a prior pointer, though of course the content of the buffer
that the prior pointer references will have been modified. Other kinds
of conversion are done in place when it is possible, but sometimes they
are not possible and in those cases prior pointers are invalidated.
The safest and easiest to remember policy is to invoke these routines
in one of the following ways:
- sqlite3_column_text() followed by sqlite3_column_bytes()
- sqlite3_column_blob() followed by sqlite3_column_bytes()
- sqlite3_column_text16() followed by sqlite3_column_bytes16()
In other words, you should call sqlite3_column_text(),
sqlite3_column_blob(), or sqlite3_column_text16() first to force the result
into the desired format, then invoke sqlite3_column_bytes() or
sqlite3_column_bytes16() to find the size of the result. Do not mix calls
to sqlite3_column_text() or sqlite3_column_blob() with calls to
sqlite3_column_bytes16(), and do not mix calls to sqlite3_column_text16()
with calls to sqlite3_column_bytes().
The pointers returned are valid until a type conversion occurs as
described above, or until sqlite3_step()
or sqlite3_reset()
or
sqlite3_finalize()
is called. The memory space used to hold strings
and BLOBs is freed automatically. Do not
pass the pointers returned
sqlite3_column_blob()
, sqlite3_column_text()
, etc. into
sqlite3_free()
.
If a memory allocation error occurs during the evaluation of any
of these routines, a default value is returned. The default value
is either the integer 0, the floating point number 0.0, or a NULL
pointer. Subsequent calls to sqlite3_errcode()
will return
SQLITE_NOMEM
.
Enable Or Disable Shared Pager Cache
int sqlite3_enable_shared_cache(int);
This routine enables or disables the sharing of the database cache
and schema data structures between connections
to the same database. Sharing is enabled if the argument is true
and disabled if the argument is false.
Cache sharing is enabled and disabled for an entire process.
This is a change as of SQLite version 3.5.0. In prior versions of SQLite,
sharing was enabled or disabled for each thread separately.
The cache sharing mode set by this interface effects all subsequent
calls to sqlite3_open()
, sqlite3_open_v2()
, and sqlite3_open16()
.
Existing database connections continue use the sharing mode
that was in effect at the time they were opened.
This routine returns SQLITE_OK
if shared cache was enabled or disabled
successfully. An error code
is returned otherwise.
Shared cache is disabled by default. But this might change in
future releases of SQLite. Applications that care about shared
cache setting should set it explicitly.
See Also: SQLite Shared-Cache Mode |
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