asio学习3: 异步tcp服务器端(datetime)

#include <ctime>
#include <iostream>
#include <boost/bind.hpp>
#include <boost/shared_ptr.hpp>
#include <boost/enable_shared_from_this.hpp>
#include <boost/asio.hpp>

using boost::asio::ip::tcp;

std::string make_daytime_string()
{
    using namespace std;
    time_t now = time(0);
    return ctime(&now);
}

/*
 从enable_shared_from_this 派生的类，
 成员函数shared_from_this返回shared_ptr

 tcp_connection类管理新连接的socket,连接后发送时间字符串至客户端
*/
class tcp_connection
    : public boost::enable_shared_from_this<tcp_connection>
{
public:
    typedef boost::shared_ptr<tcp_connection> pointer;

    static pointer create(boost::asio::io_service& io_service)
    {
        return pointer(new tcp_connection(io_service));
    }

    tcp::socket& socket()
    {
        return socket_;
    }

    void start()
    {
        message_ = make_daytime_string();
        /*
         *向新连接socket异步写数据
         *注意bind的用法(可以查看有关资料)，这里是绑定类成员函数
         *第一个参数是类成员函数地址，第二个是该类变量指针或智能指针或类变量
         *后面是传递给类成员函数的各个参数，有几个就传递几个
         */
        boost::asio::async_write(socket_, boost::asio::buffer(message_),
            boost::bind(&tcp_connection::handle_write,shared_from_this(),
            boost::asio::placeholders::error,
            boost::asio::placeholders::bytes_transferred));
    }
private:
    tcp_connection(boost::asio::io_service& io_service)
        : socket_(io_service)
    {
    }
    void handle_write(const boost::asio::error&/*error*/,
        size_t/*bytes_transferfed*/)
    {
    }
    tcp::socket socket_;
    std::string message_;
};


class tcp_server
{
public:
    tcp_server(boost::asio::io_service& io)
        : acceptor_(io, tcp::endpoint(tcp::v4(),13))
    {
        start_accept();
    }
private:
    void start_accept()
    {
        //创建新tcp_connection对象，成员变量socket_将会作为acceptor的参数
        tcp_connection::pointer new_connection =
            tcp_connection::create(acceptor_.io_service());

        //等待接受新连接
        acceptor_.async_accept(new_connection->socket(),
            boost::bind(&tcp_server::handle_accept,this,
            new_connection,boost::asio::placeholders::error));

    }

    /*
     *当async_accept接受新连接完成后呼叫handle_accept
     *我们在这个函数中响应客户请求，并等待下个连接
     */
    void handle_accept(tcp_connection::pointer new_connection,
        boost::asio::error&error)
    {
        if(!error)
        {
            new_connection->start();
            start_accept();
        }

    }
private:
    /*
    /// TCP socket 类型.
    typedef basic_stream_socket<tcp> socket;
    /// TCP acceptor 类型.
    typedef basic_socket_acceptor<tcp> acceptor;
    */
    tcp::acceptor acceptor_;
};

/*
    io_service 类为异步i/o对象的用户提供核心 i/o功能(在windows2000以上环境使用完成端口）
    如: 
        boost::asio::ip::tcp::socket
        boost::asio::ip::tcp::acceptor
        boost::asio::ip::udp::socket
        boost::asio::deadline_timer
*/
int _tmain(int argc, _TCHAR* argv[])
{
    try{
        boost::asio::io_service io;
        tcp_server server(io);
        io.run();
    }
    catch(std::exception& e)
    {
        std::cerr << e.what() << std::endl;
    }
    return 0;
}