Boost UDP 多播发送方未使用正确的端口

Question

I am following Boost UDP multicast sender tutorial here . I modify it to 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::ip::udp::endpoint endpoint_;
    boost::asio::ip::udp::socket socket_;
    boost::asio::steady_timer timer_;
    int message_count_;
    std::string message_;
    short multicast_port = 13000;
    int max_message_count = 10;

public:
    sender(boost::asio::io_context& io_context, const boost::asio::ip::address& multicast_address)
        : endpoint_(multicast_address, multicast_port),
        socket_(io_context, endpoint_.protocol()),
        timer_(io_context),
        message_count_(0)
    {
        send_periodic();
    }

private:
    void send_periodic()
    {
        static int i = 0;
        message_ = some_string();

        socket_.async_send_to(boost::asio::buffer(message_), endpoint_, [this](boost::system::error_code ec, std::size_t /*length*/)
        {
            //cout << i << endl;    // show count
            cout << i << " - " << message_; // show  count
            ++i;
        });

        timer_.expires_after(std::chrono::seconds(1));
        timer_.async_wait([this](boost::system::error_code ec)
        {
            send_periodic();
        });
    }

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

    std::string some_string()
    {
        std::string result;
        // ====================================================
        //result = "abcd";
        // ====================================================
        //os << "Message " << message_count_++;
        //result = os.str();
        // ====================================================
        //std::stringstream ss;
        //ss << i;
        //result = ss.str();
        // ====================================================
        result = make_daytime_string();

        return result;
    }
};

int main(int argc, char* argv[])
{
    // ============================================================================================================
    try
    {
        boost::asio::io_context io_context;
        //sender s(io_context, boost::asio::ip::make_address("127.0.0.1"));     // doesn't work, why?
        sender s(io_context, boost::asio::ip::make_address("239.255.0.1"));
        io_context.run();
    }
    catch (std::exception& e)
    {
        std::cerr << "Exception: " << e.what() << "\n";
    }

    return 0;
}    

The port is set to 13000. I check it with Wireshark. It shows me that the packages are sent with source port of 62910, and destination port 0. Also, the packages are not seen from another computer on the network.

I have previously tested the unicast UDP time server and client Boost provided sample codes. They work, and the port specified is correctly observed with Wireshark. Could someone tell me what went wrong?

Answer 1

成员endpoint在成员multicast_port之前初始化，因为它们被声明的顺序。