How to pass class method as an argument to another class method

December 10, 2021

I’m learning C++, and I was wondering how to pass class method as an argument to another class method. Here’s what I have now:

class SomeClass {
   private:
      // ...
   
   public:
      AnotherClass passed_func() {
          // do something
          return another_class_obj;
      }
      
      AnotherClassAgain some_func(AnotherClass *(func)()) {
          // do something
          return another_class_again_obj;
      }
      
      void here_comes_another_func() {
          some_func(&SomeClass::passed_func);
      }
};

However, this code gives error:

cannot initialize a parameter of type 'AnotherClass *(*)()' with an rvalue of type 'AnotherClass (SomeClass::*)()': different return type ('AnotherClass *' vs 'AnotherClass')

Thanks!!

>Solution :

The type of a member function pointer to SomeClass::passed_func is AnotherClass (SomeClass::*)(). It is not a pointer to a free function. Member function pointers need an object to be called, and special syntax (->*) :

struct AnotherClass{};
struct AnotherClassAgain{};

class SomeClass {
   private:
      // ...
   
   public:
      AnotherClass passed_func() {
          // do something
          return {};
      }
      
      AnotherClassAgain some_func(AnotherClass (SomeClass::*func)()) {
          (this->*func)();
          // do something
          return {};
      }
      
      void here_comes_another_func() {
          some_func(&SomeClass::passed_func);
      }
};