Call by Reference And Call by value

Aman Jen

Hi,Plz have luk @Below code:- plz explain me .....whether its call by Call by Reference Or Call by value

class Program
{
public static void Input(string C)
{
C= "ABCD";
Console.WriteLine(C);
}
static void Main(string[] args)
{
string B = "EFGH";
Program.Input(B);
Console.ReadKey();
}
}

Output : ABCD

1)Looking at the example it shows its call by value becoz , if we use call by refrence then we have to use ref keyword which is not in this case so its call by value according me.

2)But then, if it is call by value it should print "EFGH", but rather its printing "ABCD" of input method .

Why plz explain..

Thnx in Advance

4 Replies

Know the answer? Post it — somebody with the same question will find it here.

Vulpes13y ago
The local variable B contains a reference to the string "EFGH".

When this variable is passed by value to the Input method, the parameter C receives a copy of this reference.

Consequently, both B and C refer to the string "EFGH" when the method starts.

However, C is assigned a reference to the string "ABCD" within the body of the method and this value is then printed to the console.

This assignment to C doesn't change B which still refers to "EFGH". So, when the method returns and the value of B is printed to the console it's still "EFGH".

It's important to realize that B and C represent different memory locations and so are independent of each other once the method is called.
Aman Jen13y ago
Thnx for your reply...but ideally it shuld print EFGH..if its call by value..I am not getting the reason for that.....
Vulpes13y ago
I've just extended your example a bit to make this clearer:

using System;

class Program
{
public static void Input(string C)
{
C = "ABCD";
Console.WriteLine(C);
}

public static void Input(ref string C)
{
C = "ABCD";
Console.WriteLine(C);
}

static void Main(string[] args)
{
string B = "EFGH";
Program.Input(B);
Console.WriteLine(B); // still EFGH as change not persisted
Program.Input(ref B);
Console.WriteLine(B); // now ABCD as call by reference
Console.ReadKey();
}
}

The output is:

ABCD
EFGH
ABCD
ABCD
Vulpes13y ago
Yes, it is 'call by value'.

However, this doesn't prevent you from changing the value parameter within the method and printing it out.

The difference is that the change won't be persisted to the calling code as it would with a call by reference.