Boost.asio 之resolver类

1.resolver类

　　通过域名获得可用的IP，可实现与IP版本无关的网址解析

2.resolver是basic_resolver的tcp协议特化

3.内部类

　　query和iterator

4.查询IP地址

　　resolver,query,iterator

5.通过域名获得可用IP步骤

1. 创建qurey对象
2. resolve()成员函数生成iterator对象，iterator对象代表查询到的ip端点
3. socket对象尝试连接，直到找到一个可用的IP

demo

#pragma once
#include <iostream>
#include <boost/asio.hpp>
#include <boost/system/error_code.hpp>
#include <boost/asio/ip/address.hpp>
#include <boost/lexical_cast.hpp>
#include <string>
using namespace boost::asio;

class client
{
public:
    virtual ~client();

    typedef ip::tcp::socket socket_type;

private:
    io_service m_io;//web
    socket_type m_sock;

public:
　　 client(const char * name, int iport) : m_sock(m_io)
    {
        resolve_connect(m_sock, name, iport);
    }

　　 void resolve_connect(ip::tcp::socket &sock, const char * name, int port);
};

#include "pch.h"
#include "client.h"

client::~client()
{
}

void client::resolve_connect(ip::tcp::socket &sock, const char * name, int port)
{
    ip::tcp::resolver r(sock.get_io_service());
    ip::tcp::resolver::query q(name, boost::lexical_cast<std::string>(port));　　//query对象构造：域名和端口号
　　 //ip::tcp::resolver::query q("127.0.0.1", "http");　　//query对象构造：IP地址和服务名


    auto iter = r.resolve(q);
    decltype(iter) end;
    boost::system::error_code ec = error::host_not_found;
    for (; ec && iter != end; ++iter)
    {
        sock.close();
        sock.connect(*iter, ec);
    }

    if (ec)
    {
        std::cout << "can't connect." << std::endl;
        throw boost::system::system_error(ec);
    }
    std::cout << "connect success." << std::endl;
    std::cout << m_sock.remote_endpoint().address() << std::endl;
}

// WebClient.cpp : 此文件包含 "main" 函数。程序执行将在此处开始并结束。
//

#include "pch.h"
#include <iostream>
#include "client.h"

int main()
{
    try
    {
        std::cout << "web client start." << std::endl;
        client cl("www.baidu.com", 80);
    }
    catch (const std::exception& ec)
    {
        std::cout << ec.what() << std::endl;
    }
    getchar();
    std::cout << "Hello World!\n";
}