#include <stdio.h>
#include <unistd.h>
#include <stdlib.h>
#include <string.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <sys/ioctl.h>
#include <linux/if.h>

int get_iface_list(struct ifconf *ifconf)
{
   int sock, rval;

   sock = socket(AF_INET,SOCK_STREAM,0);
   if(sock < 0)
   {
     perror("socket");
     return (-1);
   }

   if((rval = ioctl(sock, SIOCGIFCONF , (char*) ifconf  )) < 0 )
     perror("ioctl(SIOGIFCONF)");

   close(sock);

   return rval;
}

int main()
{
   static struct ifreq ifreqs[20];
   struct ifconf ifconf;
   int  nifaces, i;

   memset(&ifconf,0,sizeof(ifconf));
   ifconf.ifc_buf = (char*) (ifreqs);
   ifconf.ifc_len = sizeof(ifreqs);

   if(get_iface_list(&ifconf) < 0) exit(-1);

   nifaces =  ifconf.ifc_len/sizeof(struct ifreq);

   printf("Interfaces (count = %d):\n", nifaces);
   for(i = 0; i < nifaces; i++)
   {
     printf("\t%-10s\n", ifreqs[i].ifr_name);
   }
}

[neo@techpulp ~]$ gcc ifacelist.c -o ifacelist
[neo@techpulp ~]$ ./ifacelist
Interfaces (count = 3):
        lo
        eth0
        eth1
[neo@techpulp ~]$

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Comments:

1. Ganesh

   edit

   October 27th, 2009 at 12:56 pm

   Hi Neo,

   Thanks for this article. It cleared up all my questions on using ioctl function call with SIOCGIFCONF request.

   I have made a small modification to your code. It now prints the IP address of all the interfaces configured in the computer.

   #include <arpa/inet.h>

   Code inside main loop:

   char ip_addr [ INET_ADDRSTRLEN ] ;
struct sockaddr_in *b = (struct sockaddr_in *) &(ifreqs[i].ifr_addr) ;

   printf(”\t%-10s\t%s\n”, ifreqs[i].ifr_name, inet_ntop(AF_INET, & b->sin_addr, ip_addr, sizeof ip_addr));

2. Ganesh

   edit

   October 27th, 2009 at 12:59 pm

   I am sorry, somehow none of the header file names are visible in the comment that I posted.

   Anyway, I only included ‘arpa/inet.h’ header file apart from what was already there in the code.

   Warm Regards,
   Ganesh

3. Ganesh

   edit

   October 27th, 2009 at 1:02 pm

   The code within the for loop in ‘main’ function is also missing:
   
char ip_addr [ INET_ADDRSTRLEN ] ;
struct sockaddr_in *b = (struct sockaddr_in *) &(ifreqs[i].ifr_addr) ;

   printf(”\t%-10s\t%s\n”, ifreqs[i].ifr_name, inet_ntop(AF_INET, & b->sin_addr, ip_addr, sizeof ip_addr));


4. Neo

   edit

   November 11th, 2009 at 6:23 am

   You must use &lt; for < symbol. Similarly &gt; for > symbol. It is HTML way which we can’t be avoid for now.

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