int get_addr_from_device(const char *device_name, in_addr_t *addrp){    int _sock_fd;    struct ifconf conf;    struct ifreq *ifr;    char buff[1024];    int num;    int i;    if (!addrp) {        return -1;    }    _sock_fd = socket(PF_INET, SOCK_DGRAM, 0);    if ( _sock_fd < 0 ) return -1;    conf.ifc_len = sizeof(buff);    conf.ifc_buf = buff;    if (ioctl(_sock_fd, SIOCGIFCONF, &conf) < 0) {        close(_sock_fd);        return -1;    }    num = conf.ifc_len / sizeof(struct ifreq);    ifr = conf.ifc_req;    for (i = 0; i < num; i++) {        struct sockaddr_in *sin = (struct sockaddr_in *)(&ifr->ifr_addr);        if (ioctl(_sock_fd, SIOCGIFFLAGS, ifr) < 0) {            close(_sock_fd);            return -1;        }        if ((ifr->ifr_flags & IFF_UP) && strcmp(device_name, ifr->ifr_name) == 0) {            memcpy(addrp, &(sin->sin_addr.s_addr), sizeof(in_addr_t));            close(_sock_fd);            return 0;        }        ifr++;    }    close(_sock_fd);    return -1;}