What exactly is the ->* operator?

Question

I\'ve never used it before and just stumbled upon it in an article... I thought it would be the equivalent to *x->y but apparently it isn\'t.

Here\'s

Answer 1

Its used when you have pointers to member functions.

When you have a pointer to a function of a class, you call it in much the same way you would call any member function

object.membername( ... )

or

objectptr->membername( ... )

but when you have a member function pointer, an extra * is needed after the . or -> in order that the compiler understand that what comes next is a variable, not the actual name of the function to call.

Here's an example of how its used.

class Duck
{
public:

  void quack() { cout << "quack" << endl; }
  void waddle() { cout << "waddle" << endl; }
};

typedef void (Duck::*ActionPointer)();

ActionPointer myaction = &Duck::quack;

void takeDuckAction()
{    
    Duck myduck;
    Duck *myduckptr = &myduck;

    (myduck.*myaction)();
    (myduckptr->*myaction)();
}

Answer 2

Pointer-to-Member Operators: .* and ->*

Answer 3

It defines a pointer to a member.

In an expression containing the –>* operator, the first operand must be of the type "pointer to the class type" of the type specified in the second operand, or it must be of a type unambiguously derived from that class. MSDN

Answer 4

The .* and ->* operators will point to member functions of a class or structure. The code below will show a simple example of how to use the .* operator, if you change the line: Value funcPtr = &Foo::One; to Value funcPtr = &Foo::Two; the result displayed will change to 1000 since that function is inValue*2

for example Taken From Here:

#include <iostream>
#include <stdlib.h>

class Foo { 
  public: 
    double One( long inVal ) { return inVal*1; }
    double Two( long inVal ) { return inVal*2; }
}; 

typedef double (Foo::*Value)(long inVal); 

int main( int argc, char **argv ) { 
  Value funcPtr = &Foo::One; 

  Foo foo;

  double result = (foo.*funcPtr)(500); 
  std::cout << result << std::endl;
  system("pause");
  return 0; 
}