How to call a non static member function from a static member function without passing class instance

Question

I need to call a non static member function from a static member function of the same class. The static function is a callback. It can receive only void as data, though whic

Answer 1

If your instance is a singleton (usually implemented using a private or protected constructor and a static pointer to itself) you can do e.g.:

class MyClass {
private:
  MyClass():myInstance(0) {}

  MyClass *myInstance;

  void callback();
public:
  ~MyClass() {}

  static MyClass *getInstance();

  static void myCallback();    
};

MyClass *MyClass::getInstance() {
  if(!myInstance) {
    myInstance = new MyClass;
  }
  return myInsance;
}    

void MyClass::callback() {
 // non-static callback
}

void MyClass::myCallback() {
  getInstance()->callback();
}

If you don't use a singleton but you can pass the instance cast to a void * then you can do this instead:

void MyClass::myCallback(void *data) {
  MyClass *instance = static_cast(data);
  instance->callback();
}