Incompatible function pointer

I am creating an instance of class B in a method of class A (which is a QMainWindow) with B instanceB; and then call a method of B with B.method() and pass it the function pointer of a method of A.

Now the compiler says argument of type "void (A::*)()" is incompatible with parameter of type "void (*)()". How do I resolve this if possible?

Code:

void A::method1_of_A(void)
{
    B instanceB;
    B.methodB(method2_of_A); // this is where the compiler complains
}

Parameter void (*)() can only accept a free function.

If you have parameter std::function<void()>, it can call any callable, so you can adapt your member function with a lambda capturing the object and pass that

B.methodB([&a](){ a.method2_of_A(); })

or binding the member function to the object (including <functional>)

B.methodB(std::bind(&A::method2_of_A, a))

Of course, clearest intent is in @John's comment, where you know a member function of A is expected:

void methodB(void (A::*function)()) { (this->*function)(); }