linux 获取ip地址，子网掩码源代码（摘自bacnet4linux-0.3.12）

//
//Relevent network ioctl functions
//
//SIOCGIFADDR:       /* Get interface address */
//SIOCGIFBRDADDR:    /* Get the broadcast address */
//SIOCGIFNETMASK:    /* Get the netmask for the interface */

int get_local_ifr_ioctl(char *ifname, struct ifreq *ifr, int request)
{
    int fd;
    int rv;                     // return value

    strncpy(ifr->ifr_name, ifname, sizeof(ifr->ifr_name));
    fd = socket(AF_INET, SOCK_DGRAM, IPPROTO_IP);
    if (fd < 0)
        rv = fd;
    else
        rv = ioctl(fd, request, ifr);

    return rv;
}

int get_local_address_ioctl(char *ifname, struct in_addr *addr,
    int request)
{
    struct ifreq ifr = { {{0}} };
    struct sockaddr_in *tcpip_address;
    int rv;                     // return value

    rv = get_local_ifr_ioctl(ifname, &ifr, request);
    if (rv >= 0) {
        tcpip_address = (struct sockaddr_in *) &ifr.ifr_addr;
        memcpy(addr, &tcpip_address->sin_addr, sizeof(struct in_addr));
    }

    return rv;
}

int get_local_ip_address(char *ifname, struct in_addr *addr)
{
    return get_local_address_ioctl(ifname, addr, SIOCGIFADDR);
}

int get_local_ip_broadcast_address(char *ifname, struct in_addr *addr)
{
    return get_local_address_ioctl(ifname, addr, SIOCGIFBRDADDR);
}

int get_local_ip_address_mask(char *ifname, struct in_addr *mask)
{
    return get_local_address_ioctl(ifname, mask, SIOCGIFNETMASK);
}