Question

Now how about a class’s function pointer to another class’s function? That’s my question

Example:

class Apple
{
   int(Apple::*pActionFunc)(void);
};

class Tree
{
   Apple* tempy;

   void Init( void );

   int I_Work( void );
};

void Tree::Init( void )
{
  tempy = new Apple( );
  tempy->pActionFunc = &Tree::I_Work;
}

int Tree::I_Work( void )
{
   "Do Things"
}

That will not work. Why is that?

Answer 1

This will not work, because like all variables function pointers also have an type and you can only use an pointer to same type to store address of an variable type.

int(Apple::*pActionFunc)(void); 

Tells the compiler that pActionFunc is a pointer to an member function of Apple class which takes void as an parameter and returns an int.

tempy->pActionFunc = &Tree::I_Work;

Tries to store the address of an function I_Work() which is member of Tree class an which takes void as input parameter and returns an int.

If you notice they are members functions of different classes and hence the error.