How To Declare A Pointer To A Function?

How To Declare A Pointer To A Function?

Declaring a pointer to a function is like having a tool that can point to different actions in your computer program. Instead of directly using a function, you can use this tool to choose and use different functions as needed. It’s a way to make your programs more flexible and versatile. In this guide, we’ll explain how to declare and use these function pointers in an easy-to-understand way.

How To Create a Pointer to Integer in C

int *ptrInteger; /*We have put a * operator between int 
                    and ptrInteger to create a pointer.*/

If you grasp the concept of ptrInteger being a pointer to an integer, then declaring a pointer to a function should not be too challenging. It follows a similar idea where you’re creating a tool that can point to a function instead of data. This allows you to work with functions in a flexible way. So, if you’re comfortable with it ptrInteger, you’re on the right track to understand function pointers.

How to Declare a Function

int foo(int);

When you put the * operator between int and foo(int), it signifies that you’re creating a pointer to a function. This pointer can then be used to refer to and call the foo function in your program.

You’ve hit upon an important consideration in C programming – operator precedence. Indeed, parentheses () can alter the default precedence of operators. In your case, if you want to declare a pointer to a function foo that returns an int, you need to use parentheses to ensure the * operator binds to the function name correctly. So, you would write something like int (*foo)(int). This makes it clear that foo is a pointer to a function returning an int.

Example

int (*foo)(int);

By placing the * operator with foo and using parentheses, you’ve successfully declared a pointer to a function foo that returns an int. This demonstrates a precise understanding of how to declare function pointers in C.

Refer to this example to learn more about how to declare a pointer to a function

// C Program to illustrates how to declare a function
// pointer
#include <stdio.h>
int add(int a, int b) { return a + b; }
 
int main()
{
    // Assigning function address using & operator
    int (*add_ptr)(int, int) = &add;
    // or
    // Assigning
    // function address without & operator
 
    // int (*add_ptr)(int, int) = add;
 
    // Calling the function using the function pointer
    int result = add_ptr(3, 4);
    printf("Result: %d\n", result);
 
    return 0;
}

Output

Result: 7

FAQ- How To Declare A Pointer To A Function?