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Pointer to an Array | Array Pointer

How to Declare a Pointer to a Function?

Last Updated : 19 Dec, 2024

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A pointer to a function is similar to a pointer to a variable. However, instead of pointing to a variable, it points to the address of a function. This allows the function to be called indirectly, which is useful in situations like callback functions or event-driven programming.

In this article, we will learn how to declare and use a function pointer in C.

Function Pointer Declaration

The syntax for declaring a function pointer depends on the function itself but the general syntax can be specified as:

return_type (*ptr)(parameter_types);

return_type: Return type of the function (e.g., int, void, float).
ptr: Name of the pointer to the function.
parameter_types: Types of parameters the function will accept.

Note: The parenthesis here are crucial as they set the type of the data you are declaring. Missing any of this parenthesis may declare ptr as whole different type.

Function Pointer Initialization

Once the function pointer is declared, it is then assigned the address of the function it should point to. Note that we can assign address of any function to function pointer as long as it matches the signature of the function pointer.

ptr = &func; // Using addressof operator
ptr = func; // Without using addressof operator

where, func is the name of the function.

After assigning the function pointer, we can use the ptr in place of function.

Examples of Function Pointer

The below examples of function pointer demonstrate how to use the function pointer in our C programs.

Create a Function Pointer

C

#include <stdio.h>  int add(int a, int b) { return a + b; }  int main() {    	// Declaring function pointer 	int (*fptr)(int, int);      	// Assigning address of add() functoin to fptr   	fptr = &add;  	// Calling function using function pointer 	int res = fptr(3, 4);    	printf("%d", res); 	return 0; }

Output

Pass Function as a Parameter

It is one of the most prominent applications of function pointer.

C

#include <stdio.h>  // Function to add two integers int add(int a, int b) {     return a + b; }  // Function to subtract two integers int sub(int a, int b) {     return a - b; }  int calc(int a, int b, int (*op)(int, int)) {   	return op(a, b); }  int main() {      // Using the add function     printf("%d\n", calc(5, 3, add));       // Using the subtract function     printf("%d", calc(5, 3, sub));      return 0; }

Output

8 2

Pointer to an Array | Array Pointer

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Article Tags :

C Language
pointer
C-Pointers

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