Pointer to a Function

Introduction

Pointer to a function is a way to store the memory address of a function just like a variable stores the memory address of a value. When a function is called through a pointer, it is called pointer to a function.

In this lab, we will write a C program to demonstrate how to use a pointer to a function.

Declare and define the function to be pointed to

In this step, we will declare and define a function which takes two integer arguments and does not return anything.

#include<stdio.h>

void func(int a, int b)
{
    printf("\n\n a = %d \n", a);
    printf("\n\n b = %d \n", b);
}

Declare a pointer to a function

In this step, we will declare a pointer to the function created in step 1. The syntax for declaring a pointer to a function is similar to that for declaring a pointer to a variable, but it specifies the parameter types and return type of the function being pointed to.

// function pointer
void (*fptr)(int , int);

Store the address of the function in the pointer

In this step, we will store the address of the function created in step 1 in the pointer created in step 2.

// assign address to function pointer
fptr = func;

Call the function using the pointer

In this step, we will call the function that we created in step 1 using the pointer to the function created in step 2.

// function calling
func(2,3);
fptr(2,3);  // calling a function referring to pointer to a function

Write the full code

Open the main.c file in the ~/project/ directory.

#include<stdio.h>

void func(int a, int b)
{
    printf("\n\n a = %d \n", a);
    printf("\n\n b = %d \n", b);
}

int main()
{
    printf("\n\n\t\tLabEx - Best place to learn\n\n\n");

    // function pointer
    void (*fptr)(int , int);

    // assign address to function pointer
    fptr = func;

    // function calling
    func(2,3);
    fptr(2,3);  // calling a function referring to pointer to a function

    printf("\n\n\t\t\tCoding is Fun !\n\n\n");
    return 0;
}

Compile and run the code

To compile the code, open the terminal and type the following command:

gcc main.c -o main

To run the program, type the following command:

./main

Summary

In this lab, we learned how to use a pointer to a function in a C program. We saw how to declare and define the function to be pointed to, how to declare a pointer to a function, how to store the address of the function in the pointer, and how to call the function using the pointer. The use of pointers to a function can make complex programs easier to write and understand.