Network-Programming-in-C/System_Calls/showip.c

/*
*   Printing the linked list of struct addrinfo
*/

#include <stdio.h>
#include <string.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netdb.h>
#include <arpa/inet.h>
#include <netinet/in.h>

int main(int argc, char* argv[] ){

    struct addrinfo hints, *res, *p;
    int status;
    char ipstr[INET6_ADDRSTRLEN];

    if( argc != 2 ){
        fprintf(stderr, "usage: showip hostname\n");
        return 1;
    }

    memset(&hints, 0, sizeof hints);
    hints.ai_family = AF_UNSPEC; // IP version agnostic
    hints.ai_socktype = SOCK_STREAM;

    if((status = getaddrinfo(argv[1], NULL, &hints, &res)) != 0){
        fprintf(stderr, "getaddrinfo: %s\n", gai_strerror(status));
        return 2;    
    }

    printf("IP address for %s:\n\n", argv[1]);

    for(p = res ; p != NULL ; p = p->ai_next){
        void *addr;
        char *ipver;

        // get the pointer to the address itself,
        // different fields in IPv4 and IPv6:
        if( p->ai_family == AF_INET ){
            // IPv4
            struct sockaddr_in *ipv4 = (struct sockaddr_in *)p->ai_addr;
            addr = &(ipv4->sin_addr);
            ipver = "IPv4";
        }
        else{
            // IPv6
            struct sockaddr_in6 *ipv6 = (struct sockaddr_in6 *)p->ai_addr;
            addr = &(ipv6->sin6_addr);
            ipver = "IPv6";
        }

       //convert the IP to a string and print it:
       inet_ntop(p->ai_family, addr, ipstr, sizeof ipstr);
       printf("   %s: %s\n", ipver, ipstr); 
    }

    freeaddrinfo(res); // free the linked list
    
    return 0;
}