Function Pointer

What is a Function Pointer?

A function pointer is a pointer that points to a function instead of a variable. It can be used to call a function dynamically, pass functions as arguments, and implement callbacks and event handlers.

Declaring Function Pointers

Function pointers are declared by specifying the function’s return type, followed by an asterisk (*), the pointer name, and the parameter types of the function it points to.

Syntax

return_type (*pointer_name)(parameter_types);

Example

#include <iostream>
using namespace std;

// Function to be pointed to
void display(int a) {
    cout << "Value: " << a << endl;
}

int main() {
    // Declare a function pointer
    void (*funcPtr)(int) = display;

    // Call the function using the pointer
    funcPtr(10);

    return 0;
}

In this example:

• display is a function that takes an integer parameter and returns void.
• funcPtr is a function pointer that points to display.

Using Function Pointers

Function pointers can be used in various ways, including calling functions, passing them as arguments, and storing them in arrays.

Calling Functions via Pointers

You can call a function using a function pointer just as you would call a function directly.

#include <iostream>
using namespace std;

void display(int a) {
    cout << "Value: " << a << endl;
}

int main() {
    void (*funcPtr)(int) = display;
    funcPtr(20); // Call the function using the pointer

    return 0;
}

Passing Function Pointers as Arguments

Function pointers can be passed as arguments to other functions, allowing for dynamic function calls and callbacks.

#include <iostream>
using namespace std;

void add(int a, int b) {
    cout << "Sum: " << a + b << endl;
}

void subtract(int a, int b) {
    cout << "Difference: " << a - b << endl;
}

void executeOperation(void (*operation)(int, int), int x, int y) {
    operation(x, y);
}

int main() {
    executeOperation(add, 10, 5); // Output: Sum: 15
    executeOperation(subtract, 10, 5); // Output: Difference: 5

    return 0;
}

In this example, executeOperation takes a function pointer as an argument and calls the pointed-to function with the provided parameters.

Storing Function Pointers in Arrays

You can store function pointers in arrays, allowing you to dynamically select and call functions.

#include <iostream>
using namespace std;

void add(int a, int b) {
    cout << "Sum: " << a + b << endl;
}

void subtract(int a, int b) {
    cout << "Difference: " << a - b << endl;
}

int main() {
    // Array of function pointers
    void (*operations[2])(int, int) = {add, subtract};

    // Call functions using the array
    operations[0](10, 5); // Output: Sum: 15
    operations[1](10, 5); // Output: Difference: 5

    return 0;
}