inet_ntoa在64位机器上出错

5544992

　　inet_ntoa用法如下：
　　char *inet_ntoa(struct in_addr in);就是将struct in_addr结构转换为IP地址的形式，struct in_addr这个结构应该不陌生吧，它的定义如下：
　　

struct in_addr{
unsigned long s_addr;
}
struct sockaddr_in {
short int sin_family;
unsigned short int sin_port;
struct in_addr sin_addr;
unsigned char sin_zero[8];
};
　　在服务器端使用accept函数之后，会得到客户端连接的struct sockaddr结构，然后将其转换成struct sockaddr_in结构，此时可以在服务器端得到客户端连接的IP和端口数据。
　　这时用这个函数有一个问题是：如果在64位的机器上，使用
　　char* tmp = inet_ntoa(sin->sin_addr);之后，对tmp进行操作，会出现断错误，但在32位机器上没有问题，原因是64位时inet_ntoa返回值是一个整型。


　　在网上找的两种解决办法：
　　

• 在使用的文件中，引用#include <arpa/inet.h>头文件。
  
• 直接使用inet_ntop函数。
  

　　
　　inet_ntop的说明如下：
　　NAME
inet_ntop - Parse network address structures
SYNOPSIS
#include <sys/types.h>
#include <sys/socket.h>
#include <arpa/inet.h>
const char *inet_ntop(int af, const void *src,
char *dst, socklen_t cnt);
DESCRIPTION
This  function converts the network address structure src in the af address family into a char-
acter string, which is copied to a character buffer dst, which is cnt bytes long.
inet_ntop(3)  extends  the  inet_ntoa(3)  function  to  support  multiple   address   families,
inet_ntoa(3)  is  now  considered  to  be  deprecated  in favor of inet_ntop(3).  The following
address families are currently supported:
AF_INET
src points to a struct in_addr (network byte order format) which is converted to an IPv4
network address in the dotted-quad format, &quot;ddd.ddd.ddd.ddd&quot;.  The buffer dst must be at
least INET_ADDRSTRLEN bytes long.
AF_INET6
src points to a struct in6_addr (network byte order format) which is converted to a rep-
resentation of this address in the most appropriate IPv6 network address format for this
address.  The buffer dst must be at least INET6_ADDRSTRLEN bytes long.
RETURN VALUE
inet_ntop() returns a non-null pointer to dst.  NULL is returned if there was  an  error,  with
errno set to EAFNOSUPPORT if af was not set to a valid address family, or to ENOSPC if the con-
verted address string would exceed the size of dst given by the cnt argument.
CONFORMING TO
POSIX.1-2001.  Note that RFC 2553 defines a prototype where the last parameter cnt is  of  type
size_t.  Many systems follow RFC 2553.  Glibc 2.0 and 2.1 have size_t, but 2.2 has socklen_t.