目录

利用域名获取IP地址

利用IP地址获取域名

利用域名获取IP地址

#include <netdb.h>

struct hostent* gethostbyname(const char* hostname);

成功时返回hostent结构体地址，失败时返回NULL指针。

host结构体定义如下： 

struct hostent
{
    char * h_name; //official name
    char ** h_aliases; //alias list
    int h_addrtype; //host address type
    int h_length; //address length
    char ** h_addr_list; //address list
}

 h_addr_list: 通过此变量以整数形式保存域名对应的IP地址。另外，用户较多的网站有可能分配多个IP给同一域名，利用多个服务器进行负载均衡。此时同样可以通过此变量获取IP地址信息

/*gethostbyname.c*/
#include <stdio.h>
#include <stdlib.h>
#include <arpa/inet.h>
#include <netdb.h>
#include <unistd.h>

void error_handling(char *message);

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

    host = gethostbyname(argv[1]);
    if(host == NULL)
    {
        error_handling("gethost...error");
    }
    printf("Official name: %s\n", host->h_name);
    printf("address length: %d\n", host->h_length);

    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);
}

运行结果：

mali@mali:~/code$ gcc gethostbyname.c -o gethostbyname
mali@mali:~/code$ ./gethostbyname www.taobao.com
Official name: www.taobao.com.danuoyi.tbcache.com
address length: 4
Aliases 1: www.taobao.com
Address type: AF_INET
IP addr 1: 101.89.125.220
IP addr 2: 180.163.39.80
IP addr 3: 101.89.125.219
IP addr 4: 180.163.39.79
mali@mali:~/code$ ./gethostbyname www.baidu.com
Official name: www.a.shifen.com
address length: 4
Aliases 1: www.baidu.com
Address type: AF_INET
IP addr 1: 180.101.49.12
IP addr 2: 180.101.49.11

利用IP地址获取域名