Boost.Asio学习之Buffer

朱雀 2022-07-13 12:49 224阅读 0赞

详情见：[http://www.boost.org/doc/libs/1\_61\_0/doc/html/boost\_asio/examples/cpp11\_examples.html][http_www.boost.org_doc_libs_1_61_0_doc_html_boost_asio_examples_cpp11_examples.html]  
或者：[https://github.com/NearXdu/AsioLearn][https_github.com_NearXdu_AsioLearn]

# 1.示例 #

我们经常这样写代码：

size_t read_complete(boost::system::error_code, size_t bytes){ ... }
    char buff[1024];
    read(sock, boost::asio::buffer(buff), read_complete);
    write(sock, buffer("echo\n"));

在example中，简单实现了一个buffer。

//
    //This example demonstrates how to create reference counted buffers that can be used with socket read and write operations
    #include <boost/asio.hpp>
    #include <iostream>
    #include <memory>
    #include <utility>
    #include <vector>
    
    using namespace boost::asio;
    using namespace boost::asio::ip;
    class shared_const_buffer
    {
        public:
          // Construct from a std::string.
             explicit shared_const_buffer(const std::string& data)
                 : data_(new std::vector<char>(data.begin(), data.end())),//
             buffer_(boost::asio::buffer(*data_))
        {
        }
    
             // Implement the ConstBufferSequence requirements.
             typedef boost::asio::const_buffer value_type;
             typedef const boost::asio::const_buffer* const_iterator;
             const boost::asio::const_buffer* begin() const { return &buffer_; }
             const boost::asio::const_buffer* end() const { return &buffer_ + 1; }
    
        private:
             std::shared_ptr<std::vector<char> > data_;
             boost::asio::const_buffer buffer_;
    };
    class session:public std::enable_shared_from_this<session>
    {
        public:
        session(tcp::socket socket):socket_(std::move(socket))
        {
    
        }
        void start()
        {
            do_write();
        }
    
        private:
        void do_write()
        {
            std::time_t now = std::time(0);
            //代替boost::asio::buffer
            shared_const_buffer buffer(std::ctime(&now));
    
            auto self(shared_from_this());
            boost::asio::async_write(socket_, buffer,
                [this, self](boost::system::error_code /*ec*/, std::size_t /*length*/)
                {
                });//lambda
        }
        tcp::socket socket_;
    };

# 2.streambuf简介 #

使用streambuf可以轻松的将结构体的内容写入到网络套接字中，前提是利用ostream完成简单的对<<和>>操作符的重载。  
下面的代码给出3种情况，分别是构造string、输出、写入到网络套接字。

#include <iostream>
    #include <unistd.h>
    #include <boost/asio.hpp>
    #include <boost/bind.hpp>
    using namespace std;
    struct person {
        std::string first_name, last_name;
        int age;
    };
    
    std::ostream& operator<<(std::ostream & out, const person & p) {
        return out <<"first_name: "<< p.first_name << " " <<"last_name: "<< p.last_name << " " << p.age;
    }
    std::istream& operator>>(std::istream & in, person & p) {
        return in >> p.first_name >> p.last_name >> p.age;
    } 
    
    
    int main()
    {
        boost::asio::streambuf buf;
        std::ostream out(&buf);
        person p;
        p.last_name="zhang";
        p.first_name="xiao";
        p.age=25;
        boost::system::error_code ec;
        // … 初始化p
        out << p << std::endl;
    
    #if 0
        //1.构造string
        std::ostringstream anotherout;
        anotherout<<&buf;
        string message(anotherout.str());
        cout<<message<<endl;
    #endif
    
    
    
      //  cout<<&buf<<endl;//2.输出到屏幕
    #if 1
        //3.写入到网络套接字
        boost::asio::io_service service;
    
        boost::asio::ip::tcp::socket sock(service);
    
        boost::asio::ip::tcp::endpoint ep(boost::asio::ip::tcp::endpoint(boost::asio::ip::address::from_string("127.0.0.1"),1024)
    );
    
        sock.open(boost::asio::ip::tcp::v4()); 
        sock.connect(ep);
        boost::asio::write(sock,buf,ec);
    #endif
        return 0;
    }

结果如下：  
![这里写图片描述][SouthEast]

[http_www.boost.org_doc_libs_1_61_0_doc_html_boost_asio_examples_cpp11_examples.html]: http://www.boost.org/doc/libs/1_61_0/doc/html/boost_asio/examples/cpp11_examples.html
[https_github.com_NearXdu_AsioLearn]: https://github.com/NearXdu/AsioLearn
[SouthEast]: /images/20220713/02e70ccae9b342b18687c6469244ea33.png