network programming - C code to get the IP address

Question

How do I get the IP address of the local machine using C code?

If there are multiple Interfaces then I should be able to display the IP address of each interface.

NOTE: Do not use any commands like ifconfig within C code to retrieve the IP address.

Answer 1

#include <stdio.h>
#include <string.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <sys/ioctl.h>
#include <netinet/in.h>
#include <net/if.h>

int main()
{
    int fd;
    struct ifreq ifr;

    fd = socket(AF_INET, SOCK_DGRAM, 0);

    ifr.ifr_addr.sa_family = AF_INET;

    snprintf(ifr.ifr_name, IFNAMSIZ, "eth0");

    ioctl(fd, SIOCGIFADDR, &ifr);

    /* and more importantly */
    printf("%s
", inet_ntoa(((struct sockaddr_in *)&ifr.ifr_addr)->sin_addr));

    close(fd);
}

If you want to enumerate all the interfaces, have a look at the getifaddrs() function - if you're on Linux.