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By Value or By reference C#

Expert,

I have basic question, I expect app Print 'Mary' as result, but it Print 'Mike", It looks result is changed, I didn't use word 'ref' in second call, but it treat like reference type. Could you explain why?

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace ConsoleApplication1
{
   
    class Program
    {
        static void Main(string[] args)
        {

            MyClass test = new MyClass();

            //1
            //test.strTest = "Mary";
            //SomeFunction(ref test);
            //Console.WriteLine(test.strTest);

            //2
            test.strTest = "Mary";
            SomeFunction(test);
            Console.WriteLine(test.strTest);

            Console.Read();
        }


        //static void SomeFunction(ref MyClass inst)
        //{
        //    inst.strTest = "Mike";
        //}

        static void SomeFunction(MyClass inst)
        {
            inst.strTest = "Mike";
        }
    }

    public class MyClass
    {
        public string strTest;
    }

}

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Thanks a lot.

Dmitry G

Ref has nothing to do with your result.

When you pass any string (Mary etc) to a method, you set instance string Mike. Then you print this instance string - and you see "Mike". That's it...

Specifically, this method alterates the string, and does not matter what value you set before:

        static void SomeFunction(MyClass inst)
        {
            inst.strTest = "Mike";
        }

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And yes, keep in mind, that objects are passed as referenced types :). In other words, you pass an address of your object to the method, therefore the original object is modified.

dshi15

ASKER

Thank you, but could you explain more, I'm learner and I can understand the following code from Microsoft website,

class Program
{
    static void Main(string[] args)
    {
        int arg;

        // Passing by value. 
        // The value of arg in Main is not changed.
        arg = 4;
        squareVal(arg);
        Console.WriteLine(arg);
        // Output: 4 

        // Passing by reference. 
        // The value of arg in Main is changed.
        arg = 4;
        squareRef(ref arg);
        Console.WriteLine(arg);
        // Output: 16 
    }

    static void squareVal(int valParameter)
    {
        valParameter *= valParameter;
    }

    // Passing by reference 
    static void squareRef(ref int refParameter)
    {
        refParameter *= refParameter;
    }
}

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I passed an object SomeFunction(test);
I'm confused.

dshi15

ASKER

Got it, I missed this line

>>And yes, keep in mind, that objects are passed as referenced types :). In other words, you pass an address of your object to the method, therefore the original object is modified.

You mean use 'ref ' or not, no difference here?

Dmitry G

OK, it needs a bit more explanation. With value types its pretty easy. See my comments inline:

static void Main(string[] args)
{
int arg;

// Passing by value.
// The value of arg in Main is not changed.
arg = 4;
squareVal(arg);
//anarki comment: when passing by value, we create a COPY of original value and use it //inside the method; therefore, our original value is not changed - only COPY is changed!
Console.WriteLine(arg);
// Output: 4

// Passing by reference.
// The value of arg in Main is changed.
arg = 4;
// now we do not create a copy. We, roughly speaking, pass an address of the value in the //memory (aka "pointer"). And therefore if you make some operations with this arg number //- we change the original! And when print - we print altered original!
squareRef(ref arg);
Console.WriteLine(arg);
// Output: 16
}

Hope this is pretty clear. Let me few minutes to prepare an example for objects - it's a bit more complex :).

Dmitry G

"...You mean use 'ref ' or not, no difference here?..."

There is difference but pretty subtle. I will write an example to explain.

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Dmitry G

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dshi15

ASKER

Thank you very much.