SQLITE源码剖析(3)

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　　 声明：本SQLite源码剖析系列为刘兴(http://deepfuture.iyunv.com/)原创，未经笔者授权，任何人和机构不能转载

/*
** The SQLITE_DEFAULT_MEMSTATUS macro must be defined as either 0 or 1.
** It determines whether or not the features related to
** SQLITE_CONFIG_MEMSTATUS are available by default or not. This value can
** be overridden at runtime using the sqlite3_config() API.
*/
// SQLITE_DEFAULT_MEMSTATUS宏被定义为0或1，在运行时可使
//用sqlite3_config() API修改该值
#if !defined(SQLITE_DEFAULT_MEMSTATUS)
# define SQLITE_DEFAULT_MEMSTATUS 1
#endif

/*
** Exactly one of the following macros must be defined in order to
** specify which memory allocation subsystem to use.
**该宏不一定要被定义，使用SQLITE_SYSTEM_MALLOC标准内存分配系统malloc()还是malloc()的SQLITE_MEMDEBUG调试版本
**     SQLITE_SYSTEM_MALLOC          // Use normal system malloc()
**     SQLITE_MEMDEBUG               // Debugging version of system malloc()
**
** (Historical note:  There used to be several other options, but we've
** pared it down to just these two.)
**
** If none of the above are defined, then set SQLITE_SYSTEM_MALLOC as
** the default.
*/
//SQLITE_SYSTEM_MALLOC和SQLITE_MEMDEBUG不能同时被定义
#if defined(SQLITE_SYSTEM_MALLOC)+defined(SQLITE_MEMDEBUG)>1
# error "At most one of the following compile-time configuration options\
is allows: SQLITE_SYSTEM_MALLOC, SQLITE_MEMDEBUG"
#endif
//默认使用SQLITE_SYSTEM_MALLOC标准
#if defined(SQLITE_SYSTEM_MALLOC)+defined(SQLITE_MEMDEBUG)==0
# define SQLITE_SYSTEM_MALLOC 1
#endif

/*
** If SQLITE_MALLOC_SOFT_LIMIT is not zero, then try to keep the
** sizes of memory allocations below this value where possible.
*/
// SQLITE_MALLOC_SOFT_LIMIT非0,则试图把分配的内存控制在这些值以内
#if !defined(SQLITE_MALLOC_SOFT_LIMIT)
# define SQLITE_MALLOC_SOFT_LIMIT 1024
#endif

/*
** We need to define _XOPEN_SOURCE as follows in order to enable
** recursive mutexes on most Unix systems.  But Mac OS X is different.
** The _XOPEN_SOURCE define causes problems for Mac OS X we are told,
** so it is omitted there.  See ticket #2673.
**，
** Later we learn that _XOPEN_SOURCE is poorly or incorrectly
** implemented on some systems.  So we avoid defining it at all
** if it is already defined or if it is unneeded because we are
** not doing a threadsafe build.  Ticket #2681.
**
** See also ticket #2741.
*/
//在大多数UNIX系统中，我们需要定义_XOPEN_SOURCE允许递归互斥
//对于Mac OS X, _XOPEN_SOURCE导致一些问题发生
#if !defined(_XOPEN_SOURCE) && !defined(__DARWIN__) && !defined(__APPLE__) && SQLITE_THREADSAFE
#  define _XOPEN_SOURCE 500  /* Needed to enable pthread recursive mutexes */
#endif

/*
** The TCL headers are only needed when compiling the TCL bindings.
**TCL(Tool   Command   Language)是一种解释执行的脚本语言。具有良好的跨平台特性和**可扩展性，TCL本身是用C语言实现的，可以很方便的通过C语言进行扩充，增加新的**命令，也可以很方便的把TCL解释器嵌入你的程序中。TCL解释器也是公开源代码的。
**当编译TCL绑定时，才需要TCL头文件
*/
//如果需要绑定TCL，则包括tcl.h
#if defined(SQLITE_TCL) || defined(TCLSH)
# include <tcl.h>
#endif