Code for obtaining the Mac subnet mask of the local gateway IP address in Linux

Int get_gw (char * GW) {file * FP; char Buf [1024]; char cmd [1024]; char * TMP; strcpy (CMD, "IP Route "); fp = popen (CMD, "R"); If (null = FP) {perror ("popen error"); Return-1 ;}while (fgets (BUF, sizeof (BUF), FP )! = NULL) {TMP = Buf; while (* TMP & isspace (* TMP) + + TMP; If (strncmp (TMP, "default ", strlen ("default") = 0) break;} sscanf (BUF, "% * S % s", GW ); // filter the first two strings pclose (FP); Return 0 ;}

The gateway is obtained through the IP route command.

int get_mac_ip_mask(char *ifname,char *mac1,char *ip,char *mask){    int sock;    struct ifreq ifr;    unsigned char mac[6];    sock = socket(AF_INET,SOCK_STREAM,0);    if(sock<0)    {      perror("socket error!\n");      return -1;    }        strcpy(ifr.ifr_name,ifname);        if((ioctl(sock,SIOCGIFHWADDR,&ifr) )== 0)    {      memcpy(mac,ifr.ifr_hwaddr.sa_data,6);      //printf("%s mac address is :%02X:%02X:%02X:%02X:%02X:%02X\n","eth0",mac[0],mac[1],mac[2],mac[3],mac[4],mac[5] );      sprintf(mac1,"%02X-%02X-%02X-%02X-%02X-%02X",mac[0],mac[1],mac[2],mac[3],mac[4],mac[5]);    }    else    {      perror("ioctl error!\n");      return -1;    }        if((ioctl(sock, SIOCGIFADDR, &ifr)) == 0)    {       sprintf(ip,"%.15s", inet_ntoa(((struct sockaddr_in*)&(ifr.ifr_addr))->sin_addr));    }    else    {      perror("ioctl error!\n");      return -1;    }        if((ioctl( sock, SIOCGIFNETMASK, &ifr)) == 0)    {       //sprintf(ip,"%.15s", inet_ntoa(((struct sockaddr_in*)&(ifr.ifr_addr))->sin_addr));          sprintf(mask, "%.15s",inet_ntoa((( struct sockaddr_in * )&( ifr.ifr_netmask ))->sin_addr));            }    else    {      perror("ioctl error!\n");      return -1;    }                close(sock);    return 0;  }

Ifname indicates the network port eth0 .. Mac ip masks such as eth1 are obtained through the ioctl function.