What\'s the Difference Between C \'s `->*` and `.*` Pointer-to-Member Operators?

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Demystifying the Pointer-to-Member Operators -> and . in C

Despite having explored existing resources, you may still find yourself perplexed by the enigmatic -> and . operators in C . This article aims to shed light on their true nature and clarify when their use becomes necessary.

Understanding the Purpose of Pointer-to-Member Operators

Both -> and . are pointer-to-member operators that facilitate indirect access to member functions. This intricate terminology essentially means that they enable you to invoke a member function through a pointer rather than directly from an object.

Syntax and Usage

• ->: This operator is used to dereference a pointer that points to a member function of an object. Its syntax is (ptr->member_func_ptr)().
• .: Similar to ->, this operator also dereferences a pointer to a member function. However, it is used when the pointer is dereferenced through an object's pointer or class. Its syntax is (object_ptr.*member_func_ptr)().

When to Use -> vs. .

• ->*: Use this operator when dereferencing a pointer to a member function through a pointer to an object.
• .*: Use this operator when dereferencing a pointer to a member function through an object's pointer or class.

Example

Consider a class X with the following member functions: f() and g(). Suppose you have a pointer that points to the f() function:

struct X {
  void f() {}
  void g() {}
};

typedef void (X::*pointer)();
pointer somePointer = &X::f;

To call somePointer using an object x, you would use:

X x;
(x.*somePointer)(); // Calls x.f()

If x is not an object but a pointer to an object, you can invoke the member function using ->* as follows:

X* px = new X;
(px->*somePointer)(); // Calls px->f()

This example illustrates that using ->> or . is crucial when accessing member functions indirectly through pointers, especially when dealing with pointed-to objects.

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