解析域名与IP地址

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

#define ERROR(format, args...) fprintf(stderr, format, ##args)
void getHost(const char *url, char *host);
void getIP(const char *host, char *ip, size_t n);

int main(int argc, char *argv[])
{
    if(argc !=2 )
    {
        ERROR("Usage: %s url", argv[0]);
	return -1;
    }
    char *host = (char*)malloc(sizeof(char) * (strlen(argv[1]) + 1));
    char *ip = (char*)malloc(sizeof(char) * 16);
    getHost(argv[1], host);
    getIP(host, ip, 16);
    printf("Host: %s\nIP: %s\n", host, ip);
    free(ip);
    free(host);
    return 0;
}

void getHost(const char *url, char *host)
{
    char *p = strstr(url, "://");
    if(p)
    {
        strcpy(host, p + 3);
    }
    else
    {
        strcpy(host, url);
    }
    p = strstr(host, "/");
    if(p)
    {
        *p = '\0';
    }
}

void getIP(const char *host, char *ip, size_t n)
{
    struct hostent *he = gethostbyname(host);
    assert(he);
    assert(inet_ntop(AF_INET, he->h_addr_list[0], ip, n));  ／／只取第1个IP地址
}