Linux网络编程IPv4和IPv6的inet_addr、inet_aton、inet_pton等函数小结

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);

参考：http://beej.us/guide/bgnet/output/html/multipage/inet_ntopman.html

=============================================================

IPv4：

IP字符串 ——》 网络字节流

inet_addr、inet_network、inet_aton

程序代码：

#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", ntohl(r2));   //ntohl: 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：

[[e-mail] net]$ gcc -W -o inet_addr inet_addr.c
[[e-mail] 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：

[[e-mail] net]$ gcc -W -o inet_ntoa inet_ntoa.c

[[e-mail] 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

程序代码：

#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：

[[e-mail] net]$ gcc -W -o inet_ptoa inet_ptoa.c
[[e-mail] 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

程序代码：

#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：

[[e-mail] net]$ gcc -W -o inet_ptoa6 inet_ptoa6.c
[[e-mail] net]$ ./inet_ptoa6 i6 0:0:0:0:0:FFFF:204.152.189.116
::ffff:204.152.189.116
[[e-mail] net]$ ./inet_ptoa6 i4 204.152.189.116
204.152.189.116

参考：http://www.kernel.org/doc/man-pages/online/pages/man3/inet_pton.3.html