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How to declare a pointer to a function?

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While a pointer to a variable or an object is used to access them indirectly, a pointer to a function is used to invoke a function indirectly.

Well, we assume that you know what it means by a pointer in C. So how do we create a pointer to an integer in C?

Huh..it is pretty simple…

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

Here ptrInteger is a pointer to an integer. If you understand this, then logically we should not have any problem in declaring a pointer to a function 🙂

So let us first see ..how do we declare a function?

int foo(int);

Here foo is a function that returns int and takes one argument of int type. So as a logical guy will think, putting a * operator between int and foo(int) should create a pointer to a function i.e.

int *foo(int);

But Oops..C operator precedence also plays a role here ..so in this case, operator () will take priority over operator *. And the above declaration will mean – a function foo with one argument of int type and return value of int * i.e. integer pointer. So it did something that we didn’t want to do. 🙁

So as a next logical step, we have to bind operator * with foo somehow. And for this, we would change the default precedence of C operators using () operator.

Example

int (*foo)(int);

That’s it. Here * operator is with foo which is a function name. And it did the same as what we wanted to do. So that wasn’t as difficult as we thought earlier!

Let’s see an example in C to understand how to declare a pointer to a function.

C

// 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

Last Updated : 11 Jun, 2023
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