c - Finding an interface name from an IP address

Question

I need to get the interface name by providing an IP address. There is no system call to get this.

I need an implementation for this in C or C++

Already the reverse of this is available on Stack Overflow, Finding an IP address from an interface name.

Answer 1

Use getifaddrs(3). Simple example. Usage "./foo 123.45.67.89" Please add error checking etc:

#include <stdlib.h>
#include <string.h>
#include <arpa/inet.h>
#include <net/if.h>
#include <ifaddrs.h>

int main(int argc, char *argv[]) {
  struct ifaddrs *addrs, *iap;
  struct sockaddr_in *sa;
  char buf[32];

  getifaddrs(&addrs);
  for (iap = addrs; iap != NULL; iap = iap->ifa_next) {
    if (iap->ifa_addr && (iap->ifa_flags & IFF_UP) && iap->ifa_addr->sa_family == AF_INET) {
      sa = (struct sockaddr_in *)(iap->ifa_addr);
      inet_ntop(iap->ifa_addr->sa_family, (void *)&(sa->sin_addr), buf, sizeof(buf));
      if (!strcmp(argv[1], buf)) {
        printf("%s
", iap->ifa_name);
      }
    }
  }
  freeifaddrs(addrs);
  return 0;
}