C Member Function Pointers: When to Use `->*` vs. `.`?

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Member Function Pointers in C : Demystifying >* and .

Many programmers find the pointer-to-member operators > and . in C confusing. This article clarifies their usage and when to employ them over the traditional > and ..

Understanding >* and .

> and . are pointer-to-member operators that allow you to access member functions through pointers. These operators are used when you need to dynamically bind a member function to an object.

• >*: This operator is used when the pointer and object are of the same type.
• .*: This operator is used when the pointer is of a derived type, while the object is of the base type.

Example:

Consider the following class:

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

To create a pointer to the member function f, we can use the typedef:

typedef void (X::*pointer)();

Now, we can assign f to the pointer somePointer:

pointer somePointer = &X::f;

To call the member function using the pointer, we need an object:

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

If x is a pointer to an object, we need to use >* instead:

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

Usage Scenarios:

You typically need to use > and . in scenarios where you need to pass member functions as arguments to functions or store them in containers. These operators provide a way to decouple the function call from the specific object instance.

Conclusion:

The pointer-to-member operators > and . in C are powerful tools that allow for dynamic function binding. By understanding their usage and when to employ them over the traditional > and ., you can enhance your code's flexibility and reusability.

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