gethostbyname.c

//
// Created by Administrator on 2018/12/29.
//
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <arpa/inet.h>
#include <netdb.h>

void error_handling(char *message);

int main(int argc, char *argv[]) {
    int i;
    struct hostent *host;
    if (argc != 2) {
        printf("Usage: %s <addr> \n", argv[0]);
        exit(1);
    }

    host=gethostbyname(argv[1]);
    if (!host) {
        error_handling("gethost... error");
    }

    printf("Official name: %s\n", host->h_name);
    for (i = 0; host->h_aliases[i]; ++i) {
        printf("Aliases %d: %s\n", i+1, host->h_aliases[i]);
    }
    printf("Address type: %s\n", (host->h_addrtype==AF_INET)?"AF_INET":"AF_INET6");
    for (i = 0; host->h_addr_list[i]; ++i) {
        printf("IP addr %d: %s \n", i+1, inet_ntoa(*(struct in_addr*)host->h_addr_list[i]));
    }
    return 0;
}

void error_handling(char *message) {
    fputs(message, stderr);
    fputc('\n', stderr);
    exit(1);
}