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Tip of the Day
Language: C++
Expertise: Intermediate
Dec 17, 1999

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Building the Right Environment to Support AI, Machine Learning and Deep Learning


Declaring Pointers to Member Functions

Pointers to member functions consists of the member function's return type, the class name followed by ::, the pointer's name, and the function's parameter list. For example, a pointer to a member function of class A that returns int and takes no arguments is defined like this (note that both pairs of parentheses are mandatory):

 

  class A  {
  public:
    int func ();  
  };

  int (A::*pmf) (); /* pmf is a pointer to some member 
  function of class A that returns int  and takes no 
  arguments*/

In fact, a pointer to a member functions looks just like an ordinary pointer to function, except that it also contains the class's name immediately followed by the :: operator. You can invoke the member function to which pmf points like this:

 
  pmf = &A::func; //assign pmf
  A a;
  A *pa = &a
  (a.*pmf)();  // invoke a.func() 
// call through a pointer to an object
  (pa->*pmf)();  // calls pa->func()

Pointers to member functions respect polymorphism. Thus, if you call a virtual member function through a pointer to member, the call will be resolved dynamically:

 
  class Base{
  public:
    virtual int f (int n);
  };
  class Derived : public Base {
  public:
    int f (int h); //override
  };

  Base *pb = new Derived;
  int (Base::*pmf)(int) = &Base::f;
  (pb->*pmf)(5); // call resolved as D::f(5);

Note that you cannot take the address of a class's constructor(s) and destructor.

Danny Kalev
 
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