compilation error when creating a thread with a member function with ref argument

Question

im trying to do a std::tread so i already watch some tutorial but when i do the same thing (i think) it doesnt compile.

this is my Network_ class, the "receiveFromServer" member function should be the threaded one.

class Network_ {
public:
    bool errorInfo(sf::Socket::Status status) {
        switch (status)
        {
        case sf::Socket::Done:
            return true;
            break;
        case sf::Socket::NotReady:
            std::cout << "The socket is not ready to send / receive data yet." << std::endl;
            return false;
            break;
        case sf::Socket::Partial:
            std::cout << "The socket sent a part of the data." << std::endl;
            return false;
            break;
        case sf::Socket::Disconnected:
            std::cout << "The socket has been disconnected." << std::endl;
            return false;
            break;
        case sf::Socket::Error:
            std::cout << "An unexpected error happened." << std::endl;
            return false;
            break;
        default:
            return false;
            break;
        }
    }

    void receiveFromServer(sf::RenderWindow &RW) {
        sf::Packet packet;
        std::string string;

        while (RW.isOpen())
            if (_selector.wait() && _selector.isReady(_socket)) {
                if (errorInfo(_socket.receive(packet))) {
                    packet >> string;
                    packet.clear();
                    std::cout << string << std::endl;
                }
            }
            else
                RW.close();
    }

private:
    sf::SocketSelector _selector;
    sf::TcpSocket _socket;

and this is a part of my main

Network_ network;

if (network.connectToServer(ip, port)) {
    Window_ window;
    sf::RenderWindow *RW = window.create_window("test", 10);
    std::thread receiveThread(&Network_::receiveFromServer, &network, std::ref(RW));

    return gameLoop(*RW);
}

and i got this error static assertion failed: std::thread arguments must be invocable after conversion to rvalues with a lot of sh*t underneath.

can someone help me please ? thanks :)

Answer 1

Your receiveFromServer function expects a reference to a sf::RenderWindow, but you are passing a sf::RenderWindow*&.

There are several solutions here.

Pass by value since it's just a pointer

void receiveFromServer(sf::RenderWindow* RW) // sf::RenderWindow* instead of sf::RenderWidnow&
{ /* ... */}

std::thread receiveThread(&Network_::receiveFromServer, &network, RW); // pass by value

Pass by reference - quite useless

void receiveFromServer(sf::RenderWindow*& RW) // sf::RenderWindow*& instead of sf::RenderWidnow&
{ /* ... */}

std::thread receiveThread(&Network_::receiveFromServer, &network, std::ref(RW)); // pass by reference

Pass by reference without changing your functions

void receiveFromServer(sf::RenderWindow& RW) // no change
{ /* ... */}

std::thread receiveThread(&Network_::receiveFromServer, &network, std::ref(*RW)); // dereference and pass by reference