gethostbyname.c

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

int main(int argc, char **argv) {
    if (argc < 2) {
        fprintf(stderr, "Please provide a hostname or IP...\n");
        exit(-1);
    }

    char *name = argv[1];

    struct hostent *hostinfo = gethostbyname(name);

    if (hostinfo) {
        printf("name: %s, length: %d, type: %d\n", hostinfo->h_name, hostinfo->h_length, hostinfo->h_addrtype);

        char *alias;
        for (int i = 0; alias; i++) {
            alias = hostinfo->h_aliases[i];
            if (alias)
                printf("alias number %d: %s\n", i, alias);
        }

        void *addr;
        for (int i = 0; addr; i++) {
            addr = hostinfo->h_addr_list[i];
            if (addr)
                if (hostinfo->h_addrtype == AF_INET) {
                    struct in_addr *inaddr = addr;
                    uint32_t u32addr = ntohl(inaddr->s_addr);
                    printf("address num %d: %u.%u.%u.%u\n", i, ((u32addr >> 24) & 0xFF), ((u32addr >> 16) & 0xFF), ((u32addr >> 8) & 0xFF), (u32addr & 0xFF));
                }
        }
    }
}