学步园

int main()
{
    if(check_nic("eth0") == 0)
        printf("detect ok./n");
    else
        printf("detect fail./n");
}

//如果网卡已连上网线，返回0，否则返回-1.
int check_nic(char *nic_name)
{
        struct ifreq ifr;
        int skfd = socket(AF_INET, SOCK_DGRAM, 0);

        strcpy(ifr.ifr_name, nic_name);
        if (ioctl(skfd, SIOCGIFFLAGS, &ifr) < 0)
        {
                return -1;
        }
        if(ifr.ifr_flags & IFF_RUNNING)
                return 0;  // 网卡已插上网线
else return -1;
}