Getting IPV4 address from a sockaddr structure

The following program resolves a given domain:

$ gcc a.c

$ ./a.out google.com
AF_INET: 216.58.214.238
AF_INET6: 2a00:1450:400d:803::200e

$ ./a.out google.com af_inet
AF_INET: 216.58.214.238

a.c:

#include <netdb.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <arpa/inet.h>

int
main(int argc, char *argv[])
{
    struct addrinfo hints, *res, *cres;
    int r;
    char s[INET6_ADDRSTRLEN];

    memset(&hints, 0, sizeof(hints));
    if (argc > 2)
        hints.ai_family = AF_INET;
    hints.ai_socktype = SOCK_DGRAM;

    r = getaddrinfo(argv[1], NULL, &hints, &res);
    if (r) {
        fprintf(stderr, "getaddrinfo: %s\n", gai_strerror(r));
        exit(EXIT_FAILURE);
    }

    for (cres = res; cres; cres = cres->ai_next) {
        switch (cres->ai_family) {
        case AF_INET:
            inet_ntop(AF_INET, &((struct sockaddr_in *)cres->ai_addr)->sin_addr, s, INET6_ADDRSTRLEN);
            printf("AF_INET: %s\n", s);
            break;
        case AF_INET6:
            inet_ntop(AF_INET6, &((struct sockaddr_in6 *)cres->ai_addr)->sin6_addr, s, INET6_ADDRSTRLEN);
            printf("AF_INET6: %s\n", s);
            break;
        }
    }

    freeaddrinfo(res);
}

Another example can be found here.

Type casting of sockaddr to sockaddr_in and retrieval of ipv4 using inet_ntoa

char * ip = inet_ntoa(((struct sockaddr_in *)sockaddr)->sin_addr);