Function Pointers in C

Pointers are used to point to address of some variable. Pointers can be de-referenced to get the value of the data that the pointer points to. In addition to data, pointers can also be used to store the address of a function. Not only this, it can also be de-referenced to execute the function.

Lets understand with the following example:

#include <stdio.h>

int add(int x, int y){
 return x+y;
}

int main(){

    int c;
    int (*p)(int,int);
    p = add;  // p = &add can also be used to assign the address of  add function to p.
    c=  p(2,3); // c= (*p)(2,3) can also be used to de-reference the pointer p and run the function.
    printf("%d\n",c);
}

The add function adds two integers x and y and returns the sum of two integers.

In function main, the function pointer is defined using the syntax : int (*p) (int, int).
This means that, the pointer variable p is the function pointer for a function with two integers as the input variable and an integer as the return value.

The syntax, p= add ; or p= &add; is used to store the address of add function in the pointer variable p.

The syntax, c = p(2,3) or c= *p(2,3) can be used to call the function add by de-referencing the pointer p and the return value is stored in c as c is an int variable.