程序代码：

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

int lookup_host(const char *host) {

    struct addrinfo hints, *res;
    int errcode;
    char addrstr[100];
    void *ptr;

    memset(&hints, 0, sizeof(hints));
    hints.ai_family = AF_UNSPEC;
    hints.ai_socktype = SOCK_STREAM;
    hints.ai_flags |= AI_CANONNAME;

    errcode = getaddrinfo(host, NULL, &hints, &res);
    if(errcode != 0) {
        perror("getaddrinfo");
        return -1;
    }

    printf("Host: %s\n", host);

    while(res) {
        inet_ntop(res->ai_family, res->ai_addr->sa_data, addrstr, 100);
        switch(res->ai_family) {
            case AF_INET:
                ptr = &((struct sockaddr_in *)res->ai_addr)->sin_addr;
                break;
            case AF_INET6:
                ptr = &((struct sockaddr_in6*)res->ai_addr)->sin6_addr;
                break;
        }

        inet_ntop(res->ai_family, ptr, addrstr, 100);
        printf("IPv%d address: %s (%s)\n", res->ai_family == AF_INET6? 6: 4, addrstr, res->ai_canonname);
        res = res->ai_next;
    }
    return 0;
}

int main(int argc, char *argv[]) {
    if(argc < 2) 
        exit(1);
    return lookup_host(argv[1]);
}