using members of a C Sharp class

Bill_Thompson · #1 (**permalink**) January 12th, 2009, 10:57 PM

In C Sharp, just like in C++ you can have classes with "methods" and "members" but the syntax is different.

Does anyone know how to declare a varable in a C# class so that it is accessable to other classes and code?

After I have declared a class, I have accessed the methods of the class as it appears in intellisense type as I type the class name and then a dot. But the declared members of the class does not appear.

Imar · #2 (**permalink**) January 13th, 2009, 02:43 AM

It needs to be marked as public (or internal):

Code:

 
public class TestClass
{
  public string HelloWorld()
  {
    return "Helllo World";
  }
}

Then in another class:

Console.WriteLine (new TestClass().HelloWorld());

Hope this helps,

Imar

Bill_Thompson · #3 (**permalink**) January 13th, 2009, 05:21 PM

What is the point of using set and get in C Sharp?
It seems variables are used differently in this language than in C++.
For some reason, you have to have a static variable defined like this:
public static uint Somenum
{
set { m_somenum = value; }
get { return m_somenum; }
}
and prior to this declaration, you need to have this:
public uint m_sumenum;
This seems to be the only way to expose a member of a class to other classes in C#.
The problem is that I seem to be doing this improperly because I get a compile error:
An object reference is required for the non-static field, metod, or property '.......m_somenum"
I think I see the problem. The problem is that I cannot use a static varable like this.
So you have to instantiate the class in order to set these members of the class.
So how would you do the equivalent of a global class in C Sharp?
Would I do it something like this:
public clase SomeClass
{
SomeClass someclass = new SomeClass();

public static uint Somenum
{
set { m_somenum = value; }
get { return m_somenum; }
}
}

Or perhaps this "new" needs to be outside of the class in order to work. So my next question is this. How and where would that command be such that it the internal set methods could be accessed by the other classes in the code?

Imar · #4 (**permalink**) January 13th, 2009, 05:38 PM

No no no, you're mixing things up.... Static members of a class are members of a class you can access without an instance of that class. That is, they are shared by *all* instances. For example:

Code:

 
public class Whatever
{
  private static int _counter = 0;
  public static string GetStuff
  {
    get
    {
      _counter++;
      return "Hello World " + _counter.ToString();
    }
  }
}

When you access this code like this:

Code:

Console.WriteLine (Whatever.GetStuf);

you'll get an ever increasing number each time you call this for the life time of the application.

Instance properties work on instances like this:

Code:

 
public class Whatever
{
  private int _counter = 0;
  public string GetStuff
  {
    get
    {
      _counter++;
      return "Hello World " + _counter.ToString();
    }
  }
}

First, note how _counter is private, but accessible in the public GetStuff property. There's no need to make it public as GetStuff is now non-shared as well.

Calling code like this repeatedly:

Code:

 
for (i = 0; i < 10; i++)
{
  Whatever whatever = new Whatever()
  Console.WriteLine (Whatever.GetStuf);
}

will give you a new counter with each instance. Since the counter is instance based, it gets a value of 0 every time you create a new instance. Calling the GetStuff method repeatedly on a single instance does increase the counter.

You seem to missing a few very important basics of C#. May I suggest you get a good book like Wrox's Beginning C# or Professional C#? Learning this stuff just from trying things out and comparing them with C++ may get you in troubles later. Getting the basics from a good book will definitely help you in the long run.

Edit: My example may not be the best as I am using a read-only GetStuff property to return non-related data. Typically you would use this to hide a directly related "backing variable":

Quote:

private string _firstName = string.Empty;
public string FirstName
{
get
{
return _firstName;
}
set
{
_firstName = value;
}
}

For a discussion on why properties are useful, take a look here: I have a question re: Oject Oriented Programming

Cheers,

Imar

Old Pedant · #5 (**permalink**) January 13th, 2009, 06:04 PM

Bill Thompson wrote

Quote:

you have to have a static variable defined like this:

No, no, no! Not at all true! You do not *HAVE* to use get/set property accessors if you make the data member public. It's just good OO programming technique. Many many many C++ programmer utilize similar accessors. It's just that the C++ language doesn't provide the property keyword, and so the C++ accessors don't look as "pretty". (Most C++ programmers end up using get_Name( ) and set_Name(value) methods, or similar, to make up for the lack of property keyword.)

But if a data member really is meant to be public and you can't conceive of any reason to handle it as a property, then just make it public and be done.

But *DO* read that link Imar pointed you to. We both chimed in on that one, too. LOL.

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