Linux下C编程实现---获取本机IP地址

在LINUX下，如果需要获取本机的IP地址，需要用到以下一个结构体，该结构体在/usr/include/net/if.h文件中

struct ifreq
  {
# define IFHWADDRLEN 6
# define IFNAMSIZ IF_NAMESIZE
    union
      {
    char ifrn_name[IFNAMSIZ];   /* Interface name, e.g. "en0". */
      } ifr_ifrn;

    union
      {
    struct sockaddr ifru_addr;
    struct sockaddr ifru_dstaddr;
    struct sockaddr ifru_broadaddr;
    struct sockaddr ifru_netmask;
    struct sockaddr ifru_hwaddr;
    short int ifru_flags;
    int ifru_ivalue;
    int ifru_mtu;
    struct ifmap ifru_map;
    char ifru_slave[IFNAMSIZ];  /* Just fits the size */
    char ifru_newname[IFNAMSIZ];
    __caddr_t ifru_data;
      } ifr_ifru;
  };
# define ifr_name ifr_ifrn.ifrn_name /* interface name */
# define ifr_hwaddr ifr_ifru.ifru_hwaddr /* MAC address */
# define ifr_addr ifr_ifru.ifru_addr /* address */
# define ifr_dstaddr ifr_ifru.ifru_dstaddr /* other end of p-p lnk */
# define ifr_broadaddr ifr_ifru.ifru_broadaddr /* broadcast address */
# define ifr_netmask ifr_ifru.ifru_netmask /* interface net mask */
# define ifr_flags ifr_ifru.ifru_flags /* flags */
# define ifr_metric ifr_ifru.ifru_ivalue /* metric */
# define ifr_mtu ifr_ifru.ifru_mtu /* mtu */
# define ifr_map ifr_ifru.ifru_map /* device map */
# define ifr_slave ifr_ifru.ifru_slave /* slave device */
# define ifr_data ifr_ifru.ifru_data /* for use by interface */
# define ifr_ifindex ifr_ifru.ifru_ivalue /* interface index */
# define ifr_bandwidth ifr_ifru.ifru_ivalue /* link bandwidth */
# define ifr_qlen ifr_ifru.ifru_ivalue /* queue length */
# define ifr_newname ifr_ifru.ifru_newname /* New name */
# define _IOT_ifreq _IOT(_IOTS(char),IFNAMSIZ,_IOTS(char),16,0,0)
# define _IOT_ifreq_short _IOT(_IOTS(char),IFNAMSIZ,_IOTS(short),1,0,0)
# define _IOT_ifreq_int _IOT(_IOTS(char),IFNAMSIZ,_IOTS(int),1,0,0)

从这个结构体，你可以看到ifr_addr就是我们要获取的IP地址，于是编程实现如下

#include <stdio.h>
#include <string.h>
#include <sys/socket.h>
#include <arpa/inet.h>
#include <net/if.h>
#include <sys/ioctl.h>

#define IF_NAME "eth0"

int get_local_ip(char * ifname, char * ip)
{
    char *temp = NULL;
    int inet_sock;
    struct ifreq ifr;

    inet_sock = socket(AF_INET, SOCK_DGRAM, 0); 

    memset(ifr.ifr_name, 0, sizeof(ifr.ifr_name));
    memcpy(ifr.ifr_name, ifname, strlen(ifname));

    if(0 != ioctl(inet_sock, SIOCGIFADDR, &ifr)) 
    {   
        perror("ioctl error");
        return -1;
    }

    temp = inet_ntoa(((struct sockaddr_in*)&(ifr.ifr_addr))->sin_addr);     
    memcpy(ip, temp, strlen(temp));

    close(inet_sock);

    return 0;
}

int main(void)
{
    char ip[32] = {0};

    get_local_ip(IF_NAME, ip);

    if(0 != strcmp(ip, ""))
        printf("%s ip is %s\n",IF_NAME, ip);

    return 0;
}