inet_addr()和IN_ADDR

1、inet_addr()的功能是将一个点分十进制的IPv4转换成一个长整数型数（u_long类型）

原文：The Windows Sockets inet_addr function converts a string containing an (Ipv4) Internet Protocol dotted address into a proper address for the IN_ADDR structure.

定义：unsigned long inet_addr(const char FAR *cp );

       例如：unsigned long IP = ntohl(inet_addr(192.168.0.77));

2、也可以这样使用：IN_ADDR 定义如下：

//
// IPv4 Internet address
// This is an 'on-wire' format structure.
//
typedef struct in_addr {
        union {
                struct { UCHAR s_b1,s_b2,s_b3,s_b4; } S_un_b;
                struct { USHORT s_w1,s_w2; } S_un_w;
                ULONG S_addr;
        } S_un;
#define s_addr  S_un.S_addr /* can be used for most tcp & ip code */
#define s_host  S_un.S_un_b.s_b2    // host on imp
#define s_net   S_un.S_un_b.s_b1    // network
#define s_imp   S_un.S_un_w.s_w2    // imp
#define s_impno S_un.S_un_b.s_b4    // imp #
#define s_lh    S_un.S_un_b.s_b3    // logical host
} IN_ADDR, *PIN_ADDR, FAR *LPIN_ADDR;

3、相互转换

#include <Winsock2.h>

#include <stdio.h>

int main()

{

in_addr ipAddr;

ipAddr.S_un.S_addr = inet_addr("127.0.0.1"); //将字符串形式的IP地址转换为按网络字节顺序的整形值

printf("\n%u", ipAddr.S_un);

return 0;

}