getaddrinfo

The getaddrinfo function is used to resolve both IPv4 and IPv6 hostnames. This document shows an easy example of how to use getaddrinfo on Linux platform.

Simple sample code

The following example shows you how to resolve an IPv4 address.


#include <stdio.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netdb.h>

int
main()
{
 char *hostname = "localhost";
 struct addrinfo hints, *res;
 struct in_addr addr;
 int err;

 memset(&hints, 0, sizeof(hints));
 hints.ai_socktype = SOCK_STREAM;
 hints.ai_family = AF_INET;

 if ((err = getaddrinfo(hostname, NULL, &hints, &res)) != 0) {
   printf("error %d\n", err);
   return 1;
 }

 addr.s_addr = ((struct sockaddr_in *)(res->ai_addr))->sin_addr.s_addr;

 printf("ip address : %s\n", inet_ntoa(addr));

 freeaddrinfo(res);

 return 0;
}

Please note that you would need to use freeaddrinfo to free the memory allocated by getaddrinfo. It is likely to forget using freeaddrinfo, and cause a memory leak.

see other Linux network programming articles