判斷接口是否已經打開並運行

#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <unistd.h>		
#include <sys/socket.h>
#include <sys/ioctl.h>
#include <net/if.h>
#include <sys/types.h>

#define IFNAMSIZ 16

static int IsIfUp(char *ifname);
int c;

int main( int argc, char *argv[])
{
  char *ifname;
  int status=0;

  if ( argc < 3 )
     {
        printf("Please input two arguments and try it again!\n");
        return 0;
     }

  while (( c = getopt(argc, argv, "i:")) != -1)
        {
                switch(c){
                case 'i':
                        printf("The interface is %s.\n", optarg);
                        ifname = optarg;
                        break;
                case '?':
                         printf("Please input two arguments and try it again!\n");
                         break;
                }
        }
			 
  if( (status = IsIfUp(ifname)) == 0 )
     {
     printf("The eth0 status is Up!\n");
     return 0;
     }
  else
     {
     printf("The eth0 status is down!\n");
     return -1;
    }  
}

int IsIfUp(char *ifname)
{
        struct ifreq ifr;
        int     sock;

        sock = socket(AF_INET, SOCK_DGRAM, 0);
        if(sock < 0)
        {
                perror("socket: Unable to open\n");
                return (-1);
        }

        memcpy(&ifr.ifr_name[0] ,ifname,IFNAMSIZ);
	  
        if(ioctl(sock, SIOCGIFFLAGS, &ifr) < 0 )
        {
                perror("ioctl: SIOCGIFFLAGS");
                close(sock);
                return (-1);
        }

        if (!(ifr.ifr_flags & (IFF_UP|IFF_RUNNING)))
        {
                close(sock);
                return (-1);
        }

        close(sock);	  
        return 0;

}