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C Pointer and Functions

A function pointer is nothing more than a variable that stores the address of a function. Once the address of a function is assigned to a pointer variable (function pointer), Then the respective function pointer can be used to access the function. Following simple program can clearly demonstrate the function pointer.

C Program - Function Pointer Without Return Type

pointer-functions-1.c

#include <stdio.h>
void function(); // function declaration
int main()
{
void (*ptr)(); // function pointer declaration
ptr = &function; // function pointer initialization
(*ptr)(); // Using function pointer
return 0;
}
void function() // function definition
{
printf("Access me with my address");
}

Access me with my address

Note:

In the above pointer to function program without any return type, we used void pointer (*ptr)() to hold the address of the starting point of the function, then this void pointer is used in line 7 to access the function.

C Program - Function Pointer With Return Type

pointer-functions-2.c

#include <stdio.h>
int function(); // function declaration
int main()
{
int (*ptr)(); // function pointer declaration
ptr = &function; // function pointer initialization
printf("function pointer returns %d",(*ptr)()); // Using function pointer
return 0;
}
int function() // function definition
{
int c = 4 + 4;
return c;
}

function pointer returns 8

Note:

In the above pointer to function program with return type, we used integer pointer (*ptr)() instead of void pointer to hold the address of the starting point of the function, Then this integer pointer is used to invoke the function to return the summation value of 4 + 4.

C Program - Passing Value Using Function Pointer

pointer-functions-3.c

#include <stdio.h>
int function(); // function declaration
int main()
{
int (*ptr)(); // function pointer declaration
ptr = &function; // function pointer initialization
printf("function pointer returns %d",(*ptr)(10)); // Using function pointer
return 0;
}
int function(int i) // function definition
{
int c = i + 4;
return c;
}

function pointer returns 14

Note:

The above program demonstrate that a function which is invoked by a pointer variable can be used to pass value to the function to perform some operation.

C Program - Passing Address Using Function Pointer

pointer-functions-4.c

#include <stdio.h>
int function(); // function declaration
int main()
{
int (*ptr)(), i = 6, *iptr; // function pointer declaration
iptr = &i;
ptr = &function; // function pointer initialization
printf("function pointer returns %d",(*ptr)(iptr)); // Using function pointer
return 0;
}
int function(int *i) // function definition
{
int c = *i + 4;
return c;
}

function pointer returns 10

Note:

The above program demonstrate that a function which is invoked by a pointer variable can be used to pass address of another variable to the function to perform some operation.

Did you know?

Function pointer just holds the address of staring point of a function but not the entire address in an array format.

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