擷取IP地址函數（本地、網域名稱轉換）

/* GetIp.c -- Get Local or remote Ip address by domain name* */

#include <sys/socket.h>
#include <sys/ioctl.h>
#include <net/if.h>
#include <netdb.h>
#include <string.h>
#include <errno.h>
#define h_addr h_addr_list[0]

char *
GetIp(char *dn_or_ip)
{
        struct sockaddr_in addr;
        struct hostent *host;
        struct ifreq req;
        int sock;

        if (dn_or_ip == NULL) return NULL;

        if (strcmp(dn_or_ip, "localhost") == 0) {
                sock = socket(AF_INET, SOCK_DGRAM, 0);
                strncpy(req.ifr_name, "eth0", IFNAMSIZ);

                if ( ioctl(sock, SIOCGIFADDR, &req) < 0 ) {
                        printf("ioctl error: %s/n", strerror (errno));
                        return NULL;
                }

                dn_or_ip = (char *)inet_ntoa(*(struct in_addr *) &((struct sockaddr_in *) &req.ifr_addr)->sin_addr);
                shutdown(sock, 2);
                close(sock);
        } else {
                host = gethostbyname(dn_or_ip);
                if (host == NULL) return NULL;
                dn_or_ip = (char *)inet_ntoa(*(struct in_addr *)(host->h_addr));
        }
        return dn_or_ip;
}
下面是一個測試的代碼
test_GetIp.c

#include <s

/*test_GetIp.c*/
#include <stdio.h>
#include "GetIp.c"

int
main(int argc, char *argv[])
{
        if (argc < 2) {
                fprintf(stderr, "Usage: %s domain_name or ip_address/n", argv[0]);
                return -1;
        }

        char *current_ip_address;
        current_ip_address = NULL;
        if ((current_ip_address = GetIp( argv[1])) == NULL) {
                printf ("Ip address convert error!/n");
                return -1;
        } else {
                printf("domain name or ip address : %s/n", argv[1]);
                printf("current ip address: %s/n", current_ip_address);
        }

        return 0;


具體使用示範
引文:
$./test_GetIp xxxy.lzu.edu.cn  --這裡是根據網域名稱轉換為IP地址
domain name or ip address : xxxy.lzu.edu.cn
current ip address: 202.201.0.237 

$ ./test_GetIp 219.246.79.7　--輸入地址返回地址
domain name or ip address : 219.246.79.7
current ip address: 219.246.79.7

$ ./test_GetIp localhost　　--擷取本地IP地址
domain name or ip address : localhost
current ip address: 219.246.79.4
}