Multithreading with function in other class

I’m new to c++ so sorry if obvious answer. I’m trying to get a thread to run a function from another class with an argument.

Here’s how my code is laid out:

int main(){ 
    Engine engine; 
    Sounds sounds; 
    std::thread t(&Sounds::ManageSounds, &sounds, &engine) 
    /*some stuff*/
    t.join();
} 
    
class Sounds{ 
    void ManageSounds(Engine en){ 
        /*some stuff*/ 
    } 
}

If I run this code as is, I get this error:

error: static assertion failed: std::thread arguments must be
invocable after conversion to rvalues 129 |
typename decay<_Args>::type…>::value

If I change ManageSounds() to accept no arguments and remove the &engine in the thread, it works completely fine.

>Solution :

Your thread method ManageSounds requires an Engine parameter by value, and you pass it a pointer to Engine (&engine).

To fix it you should do one of the following:

1. Pass the engine object iteslf (if it is copyable, and it makes sense in your case).
2. If you actually need pointer/reference semantics (which is quite reasonable), change the thread method accordingly. In this case you need to use std::ref (because the ctor of std::thread copies the arguments). Note: you must ensure the thread does not out-live the engine object.

Complete code example (using copy):

#include <thread>

class Engine { /*...*/ };

class Sounds {
public:
    void ManageSounds(Engine en) {
        /*some stuff*/
    }
};

int main() {
    Engine engine;
    Sounds sounds;
    //--------------------------------------------vvvvvv
    std::thread t(&Sounds::ManageSounds, &sounds, engine);
    /*some stuff*/
    t.join();
}

Complete code example (using a reference):

#include <thread>

class Engine { /*...*/ };

class Sounds {
public:
    //-----------------------v
    void ManageSounds(Engine & en) {
        /*some stuff*/
    }
};

int main() {
    Engine engine;
    Sounds sounds;
    //--------------------------------------------vvvvvvvvvvvvvvvv
    std::thread t(&Sounds::ManageSounds, &sounds, std::ref(engine));
    /*some stuff*/
    t.join();
}