Re: ip address

[Glynn Clements]

James wrote:

> if i know a device's name (eth0 etc), how can i find out it's IP address?
> i've looked in the ifconfig source but there's so much extra stuff in there
> it's hard finding the relevant bits.

Try the attached program.

-- 
Glynn Clements <[EMAIL PROTECTED]>



#include <sys/ioctl.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <net/if.h>
#include <arpa/inet.h>

#include <unistd.h>
#include <stdio.h>

static struct in_addr device_address(const char *if_name)
{
        struct ifreq ifr;
        struct sockaddr_in *addr;
        int s;

        s = socket(PF_INET, SOCK_DGRAM, 0);
        if (s == -1)
        {
                perror("socket");
                exit(1);
        }

        strcpy(ifr.ifr_name, if_name);
        ifr.ifr_name.sa_family = AF_INET;

        if (ioctl(s, SIOCGIFADDR, &ifr) < 0)
        {
                perror("ioctl(SIOCGIFADDR)");
                exit(1);
        }

        addr = (struct sockaddr_in *) &ifr.ifr_addr;

        close(s);

        return addr->sin_addr;
}

int main(int argc, char **argv)
{
        struct in_addr addr;

        if (argc < 2)
        {
                fprintf(stderr, "Usage: %s <interface>\n", argv[0]);
                exit(1);
        }

        addr = device_address(argv[1]);

        printf("IP Address: %s\n", inet_ntoa(addr));

        return 0;
}