In C++, function pointers enable users to treat functions as objects. They provide a way to pass functions as arguments to other functions. A function pointer to a member function is a pointer that points to a non-static member function of a class. In this article, we will learn how to use a function pointer to a member function in C++.

Function Pointer to Member Function in C++

In C++, functions can be treated as objects with the help of function pointers. A function pointer to a member function is a pointer that can refer to a member function of a specific class. Member functions differ from regular functions because they are associated with an instance of a class, which means they have an implicit this pointer that points to the object invoking the object. Following is the syntax to declare a function pointer to a member function:

Syntax

return_type (ClassName::*pointer_name)(argument_types) = &ClassName::member_function;

where:

• return_type: is the return type of the member function of the class.
• ClassName: is the name of the class to which the member function belongs.
• *pointer_name: is the name of the function pointer variable.
• argument_types: are the types of the arguments accepted by the member function.
• &ClassName::member_function: is the address of the member function being assigned to the function pointer.

C++ Program to Declare a Function Pointer to Member Function

The below example demonstrates how we can declare a function pointer to a member function in C++:

// C++ Program to Declare a Function Pointer to Member
// Function
#include <iostream>
using namespace std;

class MyClass {
public:
    int value;

    // Constructor to initialize the member variable 'value'
    MyClass(int val)
        : value(val)
    {
    }

    // Member function to add two integers and return the
    // result
    int add(int x, int y) { return x + y; }
};

int main()
{
    // Create an instance of MyClass with the initial value
    // of 10
    MyClass obj(10);

    // Declare a pointer to the member function 'add' of
    // MyClass
    int (MyClass::*ptrToMemberFunc)(int, int)
        = &MyClass::add;

    // Call the member function 'add' using the function
    // pointer

    int result = (obj.*ptrToMemberFunc)(20, 30);

    // Print the result of the function call
    cout << "Result from the member function: " << result
         << endl;

    return 0;
}

Result from the member function: 50

Time Complexity: O(1)
Auxiliary Space: O(1)

Explanation

• In the above example, we have defined a class MyClass with a member function add that takes two integers and returns their sum.We have then declared function pointer ptrToMemberFunc that points to the member function add.

• To call the member function using the function pointer, we have used the syntax (obj.*ptrToMemberFunc)(20, 30) where obj is the instance of the class and *ptrToMemberFunc dereferences the function pointer to call the member function with the arguments 20 and 30 of type int.