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C Function Pointer with Example

Updated on July 10, 2012

Like C variables, functions too has address and we can use this address to invoke function. So this tutorial is entirely devoted to function-pointer. But before we can call a function using we need to find out its address. So first we will see how to find memory address of a C function then we will call that function using its address.

Memory address of a C Function

#include<conio.h>
#include<stdio.h>
int show();

void main()
{
	clrscr();
	printf("Addres of show() : %u", show);
	show();
	getch();
}

int show()
{
	printf("\n\nFunction called!");
	return 0;
}

So let’s have a quick view of what this code does when you run this program. Line no 3 declares a function called “show” which has return type of integer. This is really a simple function which will print a simple message on calling. If you are new to C function then you can learn about C function here.

Line no 5-11 is main function block. In this code block only line no 8 is important for us now. This line contains a printf statement which prints address of user defined function called “show”. To print address of “show()” we only need to mention function name only in printf statement as we did in line no 8. And rest of the code is simple enough to understand.

Function pointer in C Language

In the above program we learnt how to obtain address of a function and now we will use that logic to call function using pointer. So below is a C program which is same as the above program but has some extra statements. Go through this code cautiously and right after code you will find its explanation.

#include<stdio.h>
#include<conio.h>
int show();

void main()
{
int (*fnPtr)();
clrscr();

	fnPtr=show;

	printf("Address of function :%u",show);
	(*fnPtr)();
	getch();
}

int show()
{
printf("\nFunction called using pointer!");
return 0;
}

Example of function pointer in C Language

We have declared prototype of a user defined function “show” which has integer return type. It’s a must condition for a UDF to return any data type because pointers can store address of data type (like char, int etc.). So function returning void will not work.

In our case we have function returning integer so our function pointer have to have integer type. Line no 7 declares an integer type function pointer. To declare a function pointer use the following syntax.

data-type (*function_name)();

You should write function name in bracket otherwise C compiler will throw error at compilation time as it happened in my case.

In line no 10 we are assigning address of show function to our function pointer and in line no 12 simply prints address of “show” function. Line no 13 calls our UDF using pointer. As you can see we just need to write function pointer name as we declared and it will call the function.

Line no 17-21 is “show()” declaration and I think rest is simple. But if find any difficulty then please ask me without hesitation.

Here is output of above program.

Usage of Function Pointer

Function pointer mainly used for writing memory resident programs like virus and anti virus.

C program learner's poll

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    • rajkishor09 profile image
      Author

      RAJKISHOR SAHU 5 years ago from Bangalore, Karnataka, INDIA

      Yes vijay you are right...

    • profile image

      Vijay Kanta 5 years ago

      Function pointers are mostly used in GUI programs. Example you declare a button or a dialog with button, and you want to assign a function for that button. It might sound difficult for anyone with no knowledge about it, but the functions/actions of the button are sent as pointers to the createButton() etc.. kind of functions.

    • rajkishor09 profile image
      Author

      RAJKISHOR SAHU 5 years ago from Bangalore, Karnataka, INDIA

      @Jamal : answer is there in tutorial.

    • profile image

      jamal 5 years ago

      using a function pointer as you showed does the same as just calling the function normally so i'm a bit confused as to what is the purpose of a function pointer.

      why do we use a function pointer instead of using normal function call?? please any feed back would be deeply appreciated.

    • profile image

      Pradeep 5 years ago

      Nice explaination

    • profile image

      RAHUL-MEHRAAL 5 years ago

      KAKH NI PPEYA PALLE................................9803955780

    • profile image

      sAyyAr 5 years ago

      Da sa gup dy sa 6 website na ba zda ki,

    • profile image

      aditya rajhans 5 years ago

      1 #include

      2 #include

      3

      4 void cmp(int a, int b){

      5 printf("a=%d, b=%d\n", a, b);

      6 }

      7

      8 int main(){

      9 void (*foo)(int, int);

      10 foo = cmp;

      11 foo(1, 2);

      12 return 1;

      13 }

      ::~Dude~::

      this function is returning void.....

      but u said its not possible....

    • profile image

      vignesh baskaran 5 years ago

      was help full ...........

      gave some feed!!!!!!

    • profile image

      dilipkumar mehta 5 years ago

      nice but explain and

      write with pointer

    • profile image

      nikhil singh 5 years ago

      nice one sir jee!!!!!!!!!!!!!

    • profile image

      madhu.kommu 5 years ago

      wt is the use of function pointer

    • profile image

      raja 6 years ago

      good.But pls explain very clear

    • profile image

      ck shill 6 years ago

      iam ck shill from tezpur assam

    • profile image

      surya 6 years ago

      it's good,but i have somewhat confusion about function pointers,i don't have clearance

    • profile image

      runa 6 years ago

      thanks really a very good stuff i got from this .... tutorial

    • profile image

      runa 6 years ago

      thanks really a very good stuff i got from this .... tutorial

    • profile image

      shubham 6 years ago

      thanks a lot

    • profile image

      Enayet 6 years ago

      Thanks a lot ...

    • profile image

      ankit bhujbal 6 years ago

      Create a simple calculator using the concept of function

      pointers

      can u plz help me on this code plz replay soon

      thank u

    • profile image

      kubendra 6 years ago

      it is very nice

    • profile image

      C Programmer 7 years ago

      You said "Line no 5-11 is main function block."

      Should that be lines 5-15?

    • nicomp profile image

      nicomp really 7 years ago from Ohio, USA

      Good tutorial. Arrays of pointers are also useful for writing flexible code.

    • rajkishor09 profile image
      Author

      RAJKISHOR SAHU 7 years ago from Bangalore, Karnataka, INDIA

      I am writing these tutorials for students studying c in their school, college. And in school colleges you have turbo c compiler. Thanks for your comments.