Differences between call by value and call by reference

There are call by value and call by reference methods when passing arguments to a function. Let’s learn the differences between the two methods.

Call by value

  • A method that passes only the value when passing an argument to a function
  • Even if the value of the argument is changed within the function, the value of the calling side is not changed.
  • Usually used when passing a variable
 1
 2
 3
 4
 5
 6
 7
 8
 9
10
11
12
13
14

#include <stdio.h>

void swap(int a, int b) {
    int temp = a;
    a = b;
    b = temp;
}

int main() {
    int a = 10, b = 20;
    swap(a, b);
    printf("a: %d, b: %d", a, b);
    return 0;
}

Execution result:

a: 10, b: 20

As you can see from the result, the values of a and b in the swap function have changed, but the values of a and b in the main function have not changed.

When passing large data, the call by reference method is used because the call by value method uses a lot of memory. Also, the call by value method is slow because it copies the value when calling the function.

Call by reference

  • A method that passes the address when passing an argument to a function
  • If the value of the argument is changed within the function, the value of the calling side is also changed.
  • Can be implemented using pointers
 1
 2
 3
 4
 5
 6
 7
 8
 9
10
11
12
13
14

#include <stdio.h>

void swap(int *a, int *b) {
    int temp = *a;
    *a = *b;
    *b = temp;
}

int main() {
    int a = 10, b = 20;
    swap(&a, &b);
    printf("a: %d, b: %d", a, b);
    return 0;
}

Execution result:

a: 20, b: 10

As you can see from the result, the values of a and b in the swap function have changed, and the values of a and b in the main function have also changed.

Be careful with the call by reference method because the value can be changed because the address is copied when calling the function.