not so obvious pointers

Question

I have a class :

class X{
 public :
 void f ( int ) ;
 int a ;
} ;

And the task is "Inside the code provide declarations for :

• pointer to int variable of class X
• pointer to function void(int) defined inside class X
• pointer to double variable of class X"

Ok so pointer to int a will be just int *x = &a, right ? If there is no double in X can I already create pointer to double inside this class ? And the biggest problem is the second task. How one declares pointer to function ?

Answer 1

These are called pointers to members. They are not regular pointers, i.e. not addresses, but "sort-of" offsets into an instance of the class (it gets a bit tricky with virtual functions.) So:

1. int X::*ptr_to_int_member;
2. void (X::*ptr_to_member_func)( int );
3. double X::*ptr_to_double_member;

Answer 2

You need to declare them as pointer-to-members. Pointers to members are different than usual pointers in that they are the address of a member of a structure or class, not an absolute address like regular pointers.

For more information, read this.