Call by value and call by reference

In this tutorial, we will discuss the difference between call by value and call by reference with an example.


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Call by value

If we call a function with value (variable name), the value will be duplicated and the function will receive it.


#include<stdio.h>

void print(int a)
{
   printf("From print function ...\n");
   printf("Address of a = %p\n",&a);
}

int main()
{
   int a = 10;

   printf("From Main Function ...\n");
   printf("Address of a = %p\n",&a);

   print(a);

   return 0;
}


Output

From Main Function ...

Address of a = 0x7ffee9fcfbd8

From print function ...

Address of a = 0x7ffee9fcfbbc


We can observe that the address of a in the main function and the address of a in print function are different.

So, if we change the value of a in print function, it will not affect the value of a in the main function.


/*
  * Program  : Call by value example
  * Language : C
  */

 #include<stdio.h>

 //set the argument value to 0
 void set(int a)
 {
     a = 0;
     printf("Set : In set function a = %d\n",a);
 }

 int main()
 {
     int a = 10;

     printf("Main : Before calling set function a = %d\n",a);

     set(a);

     printf("Main : After calling set function a = %d\n",a);

     return 0;
 }


Output

Main : Before calling set function a = 10

Set : In set function a = 0

Main : After calling set function a = 10


Call By Value


Call by reference

In call by reference, we pass the address of a variable.

So, if we modify the value, it will affect the original value of a variable.


#include<stdio.h>

void print(int *a)
{
  printf("From print function ...\n");
  printf("Address of a = %p\n",a);
}

int main()
{
  int a = 10;

  printf("From Main Function ...\n");
  printf("Address of a = %p\n",&a);

  print(&a);

  return 0;
}

From Main Function ...

Address of a = 0x7ffee2ea4bd8

From print function ...

Address of a = 0x7ffee2ea4bd8


We can observe that the address of a in the main function and the address of a in print function are same.


/*
 * Program  : Call by reference example
 * Language : C
 */

#include<stdio.h>

//set the argument value to 0
void set(int *a)
{
   *a = 0;
   printf("Set : In set function a = %d\n",*a);
}

int main()
{
   int a = 10;

   printf("Main : Before calling set function a = %d\n",a);

   set(&a);

   printf("Main : After calling set function a = %d\n",a);

   return 0;
}


Output

Main : Before calling set function a = 10

Set : In set function a = 0

Main : After calling set function a = 0


Call By Reference