How to pass the value of one method to another

Question

4.33/5 (2 votes)

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Hi all,

I have a method which is

C#

int x = 0; 
string a = string.Empty; 
string b = string.Empty;
MyMethod(x, a, b);

Now this method will modify the values of a and b. If this is possible then why do we need ref keyword? Or this feature is only in latest C# 4.0?

Thanks,
Ankita

Posted 31-Jan-14 21:14pm

ankum16

Updated 31-Jan-14 21:19pm

Sampath Lokuge

v2

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4 solutions

Solution 3

Primitive data types are passed by value.
Thus if you change the value of these variables inside the method, the caller values will not be affected.

To ensure the values of these variables change across the caller and the called, you can use byRef.
This feature is available in all versions.

Posted 31-Jan-14 22:20pm

Abhinav S

v2

Comments

BillWoodruff 1-Feb-14 4:51am

'byRef is VB, and the code here is in C#.

Abhinav S 1-Feb-14 7:46am

Oops. Ref for C#.

Solution 4

First of all, if you want variables 'a and 'b to be modified in the method, you don't have to pass them ! The two variables are declared outside the scope of the method, therefore any change made to them in the method will persist "outside" the method.

Passing parameters by reference is an important part of the programmer's toolbox, and you should fully understand it. In C# you need to practice using both 'ref and 'out modifiers to parameters, and understand the difference.

Both 'ref and 'out enable passing values or objects by reference: 'out does not require the passed reference to be initialized, and 'ref requires it be initialized. Assigning a value to the variable to passed using 'out before it is passed will result in a compile time error.

I suggest you study these articles by Jon Skeet very carefully: [^], [^]. If they are confusing ... too advanced for you right now ... then try Charles Petzold's book "Dot Net Zero" (free): [^].

Posted 31-Jan-14 23:11pm

BillWoodruff

Comments

ankum16 1-Feb-14 5:41am

Still I am not clear with explanation. Here lets assume I have put ref keywords while passing variables to the method. Here variables are already initialized.

MyMethod(x, ref a, ref b); And it will use the same memory location only as its reference type. Now what is difference between MyMethod(x, ref a, ref b) and MyMethod(x, a, b), if both behaves in same way.

Solution 1

visit here.....

http://www.homeandlearn.co.uk/csharp/csharp_s6p3.html[^]

Posted 31-Jan-14 21:25pm

Rakesh Meel

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V5709 · Accepted Answer · 2014-01-31T22:08:00

Solution 2

Reference parameters don't pass the values of the variables used in the function member invocation - they use the variables themselves. Rather than creating a new storage location for the variable in the function member declaration, the same storage location is used, so the value of the variable in the function member and the value of the reference parameter will always be the same. Reference parameters need the ref modifier as part of both the declaration and the invocation .

Posted 31-Jan-14 22:08pm

V5709

Comments

ankum16 1-Feb-14 5:42am

Still I am not clear with explanation. Here lets assume I have put ref keywords while passing variables to the method. Here variables are already initialized.

MyMethod(x, ref a, ref b); And it will use the same memory location only as its reference type. Now what is difference between MyMethod(x, ref a, ref b) and MyMethod(x, a, b), if both behaves in same way.

V5709 1-Feb-14 6:01am

The example that makes the difference most obvious is using string. It's a reference type but you can't change it's value in the same way you can other reference types, you have to create a new instance of the type and change the reference to point to the new instance. If you don't specify ref you can't change where the reference points to. For more refer fallowing code.. hope it will clear your point.!

-----------------------------------
class Program
{
static void Main(string[] args)
{
string changeMe = "ImTheSame";
ChangeString(changeMe);
Console.WriteLine(changeMe); //Prints: Same string as old value

ChangeString(ref changeMe);
Console.WriteLine(changeMe); //Prints: Different string
}

static void ChangeString(string changeMe)
{
changeMe = "ImDifferentNow";
}

static void ChangeString(ref string changeMe)
{
changeMe = "ImDifferentNow";
}
}
------------------------------------------