C++ Boost ASIO: initializing io_context inside class:

问题

I am following Boost UDP multicast sender tutorial here . I modify it to make a class as follow:

#define _CRT_SECURE_NO_WARNINGS
#include <ctime>
#include <iostream>
#include <string>
#include <boost/array.hpp>
#include <boost/bind.hpp>
#include <boost/shared_ptr.hpp>
#include <boost/asio.hpp>
#include <boost/lexical_cast.hpp>
#include <boost/thread.hpp>
using boost::asio::ip::udp;
using std::cout;
using std::cin;
using std::endl;

class sender
{
private:
    boost::asio::io_context io_context;
    boost::asio::ip::udp::endpoint endpoint_;
    boost::asio::ip::udp::socket socket_;
    int message_count_;
    std::string message_;
    bool showBroadcast;

public:
    // constructor
    sender(std::string multicast_address, unsigned short multicast_port, bool show = true)
    {
        boost::asio::io_context io_context;
        boost::asio::ip::udp::endpoint endpoint_(boost::asio::ip::make_address("192.168.0.255"), 13000);
        boost::asio::ip::udp::socket socket_(io_context, endpoint_.protocol());
        socket_.set_option(boost::asio::ip::udp::socket::reuse_address(true));  // no need
    }

    // destructor
    ~sender()
    {
        cout << "UDP sender exiting." << endl;
    }

private:
    std::string get_input()
    {
        std::string result;
        cout << "Enter your message: ";
        getline(cin, result);
        return result;
    }

    std::string make_daytime_string()
    {
        using namespace std; // For time_t, time and ctime;
        time_t now = time(0);
        std::string result = ctime(&now);
        return result.erase(result.length() - 1, 1);
    }

    std::string some_string()
    {
        std::string result;
        result = make_daytime_string();
        return result;
    }
};

int main(int argc, char* argv[])
{
    try
    {
        sender s("192.168.0.255", 13000);
    }
    catch (std::exception& e)
    {
        std::cerr << "Exception: " << e.what() << "\n";
    }

    return 0;
}

I wish to encapsulate io_context object inside the class, rather than having it outside. VC++ complains:

boost::asio::basic_datagram_socket': no appropriate default constructor available

I believe it is trying to force me to have the constructor as follow (which I try to move away from):

    sender(boost::asio::io_context& io_context, const boost::asio::ip::address& multicast_address, unsigned short multicast_port, bool show = true) 
    : endpoint_(multicast_address, multicast_port),
    socket_(io_context, endpoint_.protocol())

How can I possibly have everything encapsulate inside my class? Why does Boost force me to do the other way? Please help. Thank you so much.

This seems to be due to io_context being non-copyable as suggested here . I wish to have this class copyable. Any idea?

回答1:

none of the ASIO classes are copyable and most hold an io_context reference so need to be constructed with one. If you want your classes to be copyable you need to use shared pointers to the ASIO objects. I'm not sure why you would want to copy ASIO objects though as you can't use them from more than one place at a time anyway.

来源：https://stackoverflow.com/questions/49244459/c-boost-asio-initializing-io-context-inside-class

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