CODEWITHSUNDEEP
c++multithreadingtemplates
dvilela
dvilela

Reputation: 1262

Can't start C++ std::thread with callable as argument

I would like to have the following class setup in a program:

I'm having some trouble spawning the std::thread that runs the callback. It seems like I'm getting its parameters wrong, but I can't figure it out.

The minimal reproducible example:

#include <thread>

class MyClass;

class CallbackClass
{
    public:

        void (MyClass::*callback)();
        std::thread a_thread;

        void setCallback(void (MyClass::*cb)())
        {
            callback = cb;
        }

        void writeCall()
        {
            a_thread = std::thread(callback); // error here
        }
};

class MyClass
{
    public:

        CallbackClass callbackobject;

        MyClass()
        {
            callbackobject.setCallback(&MyClass::bufferWriter);
        }

        void bufferWriter(){}
};

int main(){}

The compiler error I get:

error: no matching function for call to ‘std::thread::_Invoker<std::tuple<void (MyClass::*)()> >::_M_invoke(std::thread::_Invoker<std::tuple<void (MyClass::*)()> >::_Indices)’
  operator()()

on this line:

a_thread = std::thread(callback); // error here

Upvotes: 0

Views: 594

Answers (1)

Sam Varshavchik
Sam Varshavchik

Reputation: 118350

void (MyClass::*callback)();

This is a pointer to a class method.

a_thread = std::thread(callback);

A class method is not a function that can be called by itself. The class method requires an object for which it gets invoked. You need to store, or obtain a pointer to a MyClass object, from somewhere. For example, you can pass a 2nd parameter to `setCallback:

void setCallback(void (MyClass::*cb)(), MyClass *ptr)

and then stash it away, somewhere, then use it to invoke the class method. Typically, this would be something like:

a_thread = std::thread(callback, ptr);

Upvotes: 2

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