Function Pointer in C

January 17, 2023

Function Pointer :

Function pointers in C are variables that can be used to construct function calls to functions pointed by them by storing the memory address of the functions in them.

Syntax :

return_type  (*ptr_name)  (type1, type2);

Example :

The below program is explaining the working of function pointer in C.

Run

#include<stdio.h>

void help(int val)
{
    printf("Value of val is %d\n", val);
}
  
int main()
{
    // pointer to function declaration 
    void (*help_ptr)(int) = &help;
    (*help_ptr)(20);
  
    return 0;
}

Output :

Value of val is 20

What happened above? In the program, we write the help function and by declaring the function pointer void (*help_ptr) (int) we passed the value of the variable.

Pointers in C

Pointer to arithmetic in C

Null pointer

Function Pointer as an argument

Pointer v/s array

Features of Function Pointer :

A function pointer, in contrast to other pointers, points to code rather than data.
Usually, the beginning of executable code is stored in a function pointer.
Switch case can be substituted with a function pointer.
A function pointer can be supplied as an argument and can also be returned from a function, just like regular data pointers can.
In C, function pointers can be utilised to create calls to the functions they point to.This enables programmers to send them as parameters to functions.Callback functions are another name for such functions that are supplied as arguments to other functions.
Pointers are one type of value that functions can accept and return.Changes made to pointers when they are supplied as function arguments remain after the function has finished.Passing pointers to function arguments in this manner is known as pass by reference.

Examples :

Let,s see some example for better understanding the function pointer in C

Example 1

Run

#include<stdio.h>
// function to find the smmaler value between two integer
int *smaller(int *val_1, int *val_2) {
    if (*val_1 < *val_2) {
        return val_1;
    }
    return val_2;
}
int main() {
    int val_1 = 20, val_2 = 30;
    int *val;

     // calling the function
    val = smaller(&val_1, &val_2);
    printf("Smallest value is  = %d", *val);
    return 0;
}

Output :

Smallest value is  = 20

What Happened Above? In the above pointer function is used to called the smaller function to print the smaller value between the two values.

Example 2

Run

#include<stdio.h>
// function for addition of two integer
int addition(int val_1, int val_2) {
    int sum = val_1 + val_2;
    return sum;
}


int main() {
    int a, b, summation;
    a= 100;
    b= 200;
    // declaration of function pointer
    int (*fp)(int, int); 
    fp = addition;
    summation = (*fp)(a, b); 
    
    printf("Sum of two values = %d", summation);
    return 0;
}

Output :

Sum of two values = 300

What Happened Above? In the above program, we write a addition function to add the two integers and used function pointer to call the addition function .

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Function Pointer in C