ioctl函数，可以获取ip地址，修改ip地址,网卡地址等

部分转自http://www.cnblogs.com/zht-blog/p/4025903.html

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

unsigned char g_eth_name[16];
unsigned char g_macaddr[6];

unsigned int g_broadcast_addr;

int main()
{
    int i;
    int rv;
    int fd;
    struct ifreq ifr;
    struct sockaddr_in sin;
    char ipaddr[50];

fd = socket(AF_INET, SOCK_STREAM, 0);
    if (-1 == fd)
    {
        return;
    }

strcpy(g_eth_name, "eth0");
    strcpy(ifr.ifr_name, g_eth_name);

if ( ioctl(fd, SIOCGIFHWADDR, &ifr) < 0)
    {
        close( fd );
        return;
    }
    memcpy(g_macaddr, ifr.ifr_hwaddr.sa_data, sizeof(g_macaddr));
    printf("local mac:");
    for(i=0;i<sizeof(g_macaddr)-1;i++)
    {
        printf("%.2x:", g_macaddr[i]);
    }
    printf("%.2x\n", g_macaddr[i]);

//get the broadcast addr
    if ( ioctl(fd, SIOCGIFBRDADDR, &ifr) < 0)
    {
        close( fd );
        return;
    }
    memcpy(&sin, &ifr.ifr_addr, sizeof(sin));
    g_broadcast_addr = sin.sin_addr.s_addr;
    printf("broadcast is :%s\n", inet_ntoa(sin.sin_addr));

//set the mask

struct sockaddr_in *sin_net_mask;
    memset(&ifr, 0, sizeof(ifr));
    strncpy(ifr.ifr_name, "eth0", sizeof(ifr.ifr_name )-1);
    sin_net_mask = (struct sockaddr_in *)&ifr.ifr_addr;
    sin_net_mask->sin_family = AF_INET;
    inet_pton(AF_INET, "255.255.255.0", &sin_net_mask ->sin_addr);

if (ioctl(fd, SIOCSIFNETMASK, &ifr ) < 0)
    {
        close( fd );
        printf("set net mask error:%s\n", strerror(errno));
        return;
    }

close( fd );