C语言中使用正则表达式一般分为三步:

1. 编译正则表达式 regcomp()
2. 匹配正则表达式 regexec()
3. 释放正则表达式 regfree()

下边是对三个函数的详细解释：

#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <unistd.h>
#include <errno.h>
#include <
#include <netdb.h>

#define SERVER_PORT    80
#define SERVER_DOMAIN_NAME    "api.help.bj.cn"

void sys_err(const char *str)
{
    perror(str);
    exit(1);
}

int main(int argc, char *argv[])
{
    struct hostent *host_info;

    host_info = gethostbyname(SERVER_DOMAIN_NAME);
    if(host_info == NULL){
        sys_err("hostInfo is NULL\r\n");
        return -1;
    }

     printf("host name:%s\r\n", host_info->h_name);
    //  printf("alias list:%s\r\n", host_info->h_aliases);
    // printf("type:%d\r\n", host_info->h_addrtype);
    // printf("length:%d\r\n", host_info->h_length);
    // printf("address list:%s\r\n",host_info->h_addr_list);

    // close(sfd);
    
    return 0;
}