리눅스 ioctl() 함수사용하여 IP정보 얻어오는데요..

    struct ifreq *ifr;
    struct sockaddr_in *sin;
 
    struct ifconf ifcfg;
    int fd;
    int n;
    int numreqs = 30;
    fd = socket(AF_INET, SOCK_DGRAM, 0);
 
    memset(&ifcfg, 0, sizeof(ifcfg));
    ifcfg.ifc_buf = NULL;
    ifcfg.ifc_len = sizeof(struct ifreq) * numreqs;
    ifcfg.ifc_buf = (char*)malloc(ifcfg.ifc_len);
 
    for(;;)
    {
        if (ioctl(fd, SIOCGIFCONF, (char *)&ifcfg) < 0)
        {
            close(fd);
            return -1;
        }
        break;
    }
 
    ifr = ifcfg.ifc_req;
 
    for (n = 0; n < ifcfg.ifc_len; n+= sizeof(struct ifreq))
    {
        sin = (struct sockaddr_in *)&ifr->ifr_addr;
 
        if(sin != NULL)
        {
            memcpy(LocalIP[nLocalIPCnt],inet_ntoa(sin->sin_addr),strlen(inet_ntoa(sin->sin_addr))+1);
            nLocalIPCnt ++;
        }
 
        ifr++;
    }