ref class member variable - C# Discussion Boards

27-Jan-04 6:47

Hi everyone,

I am pretty new to C#. So, this might be a really newbie question.

How can I have a member variable that is a reference.

I can have ref parameters as:

<br />
public void SomeFunc(ref int i)<br />
{<br />
  i = 5; // no probs<br />
}

However, I want to do something like this and I cannot figure out a way to do it:

<br />
public class Test<br />
{<br />
  public Test(ref int i)<br />
  {<br />
     m_i = i;<br />
  }<br />
  private ref int m_i;<br />
}

Any suggestions would be appreciated.

Thanks,
Pankaj

Without struggle, there is no progress

John Fisher27-Jan-04 6:51

27-Jan-04 6:51

The code example that you gave has no need of the "ref" concept. If you remove "ref" from that sample, things will behave as you expect.

So, can you explain better what you are actually trying to accomplish?

John

"You said a whole sentence with no words in it, and I understood you!" -- my wife as she cries about slowly becoming a geek.

pankajdaga27-Jan-04 7:08

27-Jan-04 7:08

Well, this does not work as expected (or my expectations are completely flawed)

public class Test
{
public Test(ref int i)
{
m_i = i;
m_i = 10; //this does not change the value of i in the calling func.
}
private ref int m_i;
}

Without struggle, there is no progress

John Fisher27-Jan-04 7:28

27-Jan-04 7:28

Are you trying to make m_i into a pointer to i? If so, then I understand what you're trying to do.

In explanation, the code is taking the value if i and assigning it to m_i, then taking the value of 10 and assigning it to m_i. The attempt to make m_i into a pointer to i is where your expectations have met the problem.

In C#, all class objects are handled "by reference". In other words, every time you to a "new Test()", you are getting a pointer to the real object. This means that whenever you put "myvar = something", you are setting pointers -- NOT copying objects. (Copy constructors only come into play when you explicitly use the "new" keyword.)

That said, you may already have a better technique to achieve your goal. However, you could do something like this:

public class Storage
{
    int value;
}

public class Test
{
    public Test(Storage val)
    {
        m_val = val;
        m_val.value = 10;
    }
    private Storage m_val;
}

John

"You said a whole sentence with no words in it, and I understood you!" -- my wife as she cries about slowly becoming a geek.

pankajdaga27-Jan-04 8:22

27-Jan-04 8:22

Ahhhhhhhh... I did not know that.

So, just to make sure that I understand...

Everytime that I pass parameters to functions etc., I am always passing a pointer to the object and not invoking a full copy of it.

If this is indeed the case, then I do not need the ref keyword.

Thanks,
Pankaj

Without struggle, there is no progress

Heath Stewart27-Jan-04 8:45

Heath Stewart

27-Jan-04 8:45

As Nick explained, though, value types (such as int, long, byte, enum, structs, etc.) are just that - value types. You pass a value to a method (not function - methods are "functions" that belong to an entity such as a class, interface, or struct). In almost all cases, this is just fine. When you pass a reference (everything else), a reference to the original object is stored in the stack (internal to the CLR). Using ref and out with value types is common, however, when P/Invoking native functions.

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Nick Parker27-Jan-04 6:54

Nick Parker

27-Jan-04 6:54

With .NET you have value and reference types. Classes are always reference types. You don't need to declair int m_i as a reference type because it is a member of an object of type Test, so you are using it via an instance. Just make sure when you use methods inside your class that change that value that you mark the parameter as ref. Does that help.

- Nick Parker
My Blog

pankajdaga27-Jan-04 7:11

27-Jan-04 7:11

Hi,

Can you show a small example, if you do not mind.

The things is I want to change the object in the calling function from this instance. I actually want a reference because I do not want to call the copy constructor on a large object.

I miss C++ Smile | :)

Thanks,
Pankaj

Without struggle, there is no progress

Nick Parker27-Jan-04 7:28

Nick Parker

27-Jan-04 7:28

Here is a quick example:

public class Test
{
    public Test(){}

    public int MyNumber
    {
        get{return m_i;}
        set{m_i = value;}
    }

    public int m_i;
}

public class SomeOtherClass
{
    public SomeOtherClass(){}


    public void ChangeValue(ref int i)
    {
        i = 5;
    }
}

    // Example
Test t = new Test();
SomeOtherClass soc = new SomeOtherClass();
t.MyNumber = 8;
soc.ChangeValue(ref t.m_i);
Console.Write(t.MyNumber);

- Nick Parker
My Blog

WebSvcs vs Remoting

Kant27-Jan-04 6:24

Kant

27-Jan-04 6:24

What are the differences between them?
How do I make decision on choosing on of them in my project?
(ASP.NET (must be thin client)
-> {?? WebSvc/Remoting}
-> Data Access Layer(ADO.NET)
-> DB)

Is there any link on MSDN or anywhere on the web which explains in detail.

TIA

Promise only what you can do. And then deliver more than what you promised.
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Re: WebSvcs vs Remoting

Heath Stewart27-Jan-04 6:36

Heath Stewart

27-Jan-04 6:36

Web Services by nature are one-way communications since they use HTTP. .NET Remoting allows you to use TCP or HTTP channels, so communications can be two-way (i.e., the server can also talk to the client). .NET Remoting also allows you to chain sinks together (know as Aspect-Oriented Programming, or AOP) that allows you to work on the messages and add or change things as the formatted messages go through the sink chain.

.NET Remoting also allows you to use a binary formatter as opposed to a SOAP formatter (which Web Services use) which is much faster when serializing object graphs and uses less bandwidth to transmit.

For a comparison of ASP.NET/Web Services vs. .NET Remoting, see http://msdn.microsoft.com/library/en-us/cpguide/html/cpconchoosingcommunicationoptionsinnet.asp[^]. This also contains links to more information regarding each of the technologies.

Re: WebSvcs vs Remoting

Kant27-Jan-04 6:47

Kant

27-Jan-04 6:47

I was hoping that you would reply. Big Grin | :-D

Thanks for clarifying me.

Meanwhile I found a link[^] at MSDN but that's old link, that too related VB.

Promise only what you can do. And then deliver more than what you promised.
This signature was created by "Code Project Quoter".

Re: WebSvcs vs Remoting

Uwe Keim28-Jan-04 3:11

Uwe Keim

28-Jan-04 3:11

The best place I found is www.ingorammer.com [^], an Austrian guy from which I also bought a book now.

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Custom controls

Radoslav Bielik27-Jan-04 6:01

Radoslav Bielik

27-Jan-04 6:01

Hi everyone,

I'm using VS.NET 2003 to develop WIndows Forms applications - my question is, when I add a user control to a control library project that is part of my solution, it automatically appears in the "My User Controls" section of the VS toolbox. Is it possible to have VS automatically recognize my custom controls as well or not?

Thanks Smile | :)

rado

Radoslav Bielik
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John Fisher27-Jan-04 6:54

27-Jan-04 6:54

In my experience that happens automatically when you compile your control.

John

"You said a whole sentence with no words in it, and I understood you!" -- my wife as she cries about slowly becoming a geek.

Radoslav Bielik27-Jan-04 6:57

Radoslav Bielik

27-Jan-04 6:57

For me it happens only for user controls upon compilation, but not for custom controls Frown | :(

Is it possible to configure it somewhere?

rado

Radoslav Bielik
http://www.neomyz.com/poll [^] - Get your own web poll

John Fisher27-Jan-04 7:12

27-Jan-04 7:12

I didn't understand that there was a difference between the two. What do you mean by "custom control"?

John

"You said a whole sentence with no words in it, and I understood you!" -- my wife as she cries about slowly becoming a geek.