转载 http://blog.csdn.net/ithomer/article/details/6100734

知识背景：

210.25.132.181属于IP地址的ASCII表示法，也就是字符串形式。英语叫做IPv4 numbers-and-dots notation。
如果把210.25.132.181转换为整数形式，是3524887733，这个就是整数形式的IP地址。英语叫做binary data。（其实binary是二进制的意思）
详细介绍，请参考： 网络字节序与主机字节序的转换

问题所在：

如何在字符串形式的IP和整数形式的IP之间转换呢？

转换函数：

int inet_aton(const char *cp, struct in_addr *inp);
in_addr_t inet_addr(const char *cp);
in_addr_t inet_network(const char *cp);
int inet_pton(int af, const char *src, void *dst);
const char *inet_ntop(int af, const void *src, char *dst, socklen_t cnt);

IPv4：

IP字符串 ——》 网络字节流
inet_addr、inet_network、inet_aton

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>
#include <netinet/in.h>
#include <sys/socket.h>
#include <sys/types.h>

int main()
{
    char ip[] = "192.168.0.74";
    long r1, r2, r3;  //long
    struct in_addr addr;

    r1 = inet_addr(ip); //返回网络字节序
    if(-1 == r1){
        printf("inet_addr return -1/n");
    }else{
        printf("inet_addr ip: %ld/n", r1);
    }
    
    r2 = inet_network(ip);    //返回主机字节序
    if(-1 == r2){
        printf("inet_addr return -1/n");
    }else{
        printf("inet_network ip: %ld/n", r2); 
        printf("inet_network ip: %ld/n", htonl(r2));   //htonl: 主机字节序 ——> 网络字节序
    }
    
    r3 = inet_aton(ip, &addr);  //返回网络字节序
    if(0 == r3){
        printf("inet_aton return -1/n");
    }else{
        printf("inet_aton ip: %ld/n", addr.s_addr);
    }

/*****  批量注释的一种方法  *****/
#if 0  
    r3 = inet_aton(ip, addr);
    if(0 == r3){
        printf("inet_aton return -1/n");
    }else{
        printf("inet_aton ip: %ld/n", ntohl(addr.s_addr));
    }
#endif

    return 0;
}

运行结果：

[work@db-testing-com06-vm3.db01.baidu.com net]$ gcc -W -o inet_addr inet_addr.c 
[work@db-testing-com06-vm3.db01.baidu.com net]$ ./inet_addr                     
inet_addr ip: 1241557184
inet_network ip: -1062731702
inet_network ip: 1241557184
inet_aton ip: 1241557184

IP字符串 《——》 网络字节流
inet_addr、inet_aton、inet_ntoa

程序代码：

#include <stdio.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <string.h>
int main(int argc, char *argv[])
{
    char ip1[] = "192.168.0.74";
    char ip2[] = "211.100.21.179";
    struct in_addr addr1, addr2;
    long l1, l2;
    l1 = inet_addr(ip1);   //IP字符串——》网络字节
    l2 = inet_addr(ip2);
    printf("IP1: %s/nIP2: %s/n", ip1, ip2);
    printf("Addr1: %ld/nAddr2: %ld/n", l1, l2);
    
    memcpy(&addr1, &l1, 4); //复制4个字节大小
    memcpy(&addr2, &l2, 4);
    printf("%s <--> %s/n", inet_ntoa(addr1), inet_ntoa(addr2)); //注意：printf函数自右向左求值、覆盖
    printf("%s/n", inet_ntoa(addr1)); //网络字节 ——》IP字符串
    printf("%s/n", inet_ntoa(addr2));
    return 0;
}

运行结果：

[work@db-testing-com06-vm3.db01.baidu.com net]$ gcc -W -o inet_ntoa inet_ntoa.c 
[work@db-testing-com06-vm3.db01.baidu.com net]$ ./inet_ntoa                                      
IP1: 192.168.0.74
IP2: 211.100.21.179
Addr1: 1241557184
Addr2: 3004523731
192.168.0.74 <--> 192.168.0.74
192.168.0.74
211.100.21.179

IPv6：

IPv4 字符串 《——》网络字节流
inet_pton、inet_ntop

#include <stdio.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <arpa/inet.h>

int main()
{
    char ip[] = "192.168.0.74"; 
    struct in_addr addr;
    
    int ret = inet_pton(AF_INET, ip, (void *)&addr);   //IP字符串 ——》网络字节流
    if(0 == ret){
        printf("inet_pton error, return 0/n");
        return -1;
    }else{
        printf("inet_pton ip: %ld/n", addr.s_addr);
        printf("inet_pton ip: 0x%x/n", addr.s_addr);
    }

    const char *pstr = inet_ntop(AF_INET, (void *)&addr, ip, 128);  //网络字节流 ——》IP字符串
    if(NULL == pstr){
        printf("inet_ntop error, return NULL/n");
        return -1;
    }else{
        printf("inet_ntop ip: %s/n", ip);
    }
    
    return 0;
}

运行结果：

[work@db-testing-com06-vm3.db01.baidu.com net]$ gcc -W -o inet_ptoa inet_ptoa.c 
[work@db-testing-com06-vm3.db01.baidu.com net]$ ./inet_ptoa                     
inet_pton ip: 1241557184
inet_pton ip: 0x4a00a8c0
inet_ntop ip: 192.168.0.74

IPv6 字符串 《——》网络字节流
inet_pton、inet_ntop

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <arpa/inet.h>

int 
main(int argc, char **argv)
{
    unsigned char buf[sizeof(struct in6_addr)];
    int domain, s;
    char str[INET6_ADDRSTRLEN];

    if(argc != 3){
        fprintf(stderr, "usage: %s {i4|i6|<num>} string/n", argv[0]);
        exit(EXIT_FAILURE);
    }

    domain = (strcmp(argv[1], "i4") == 0) ? AF_INET:(strcmp(argv[1], "i6") == 0) ? AF_INET6 : atoi(argv[1]);
    
    //IP字符串 ——》网络字节流
    s = inet_pton(domain, argv[2], buf);
    if(s<=0){
        if(0 == s)
            fprintf(stderr, "Not in presentation format/n");
        else
            perror("inet_pton");
        exit(EXIT_FAILURE);
    }

    //网络字节流 ——》IP字符串
    if(inet_ntop(domain, buf, str, INET6_ADDRSTRLEN) == NULL){  
        perror("inet ntop/n");
        exit(EXIT_FAILURE);
    }

    printf("%s/n", str);
    exit(EXIT_SUCCESS);
}

运行结果：

[work@db-testing-com06-vm3.db01.baidu.com net]$ gcc -W -o inet_ptoa6 inet_ptoa6.c                               
[work@db-testing-com06-vm3.db01.baidu.com net]$ ./inet_ptoa6 i6 0:0:0:0:0:FFFF:204.152.189.116   
::ffff:204.152.189.116
[work@db-testing-com06-vm3.db01.baidu.com net]$ ./inet_ptoa6 i4 204.152.189.116               
204.152.189.116