is null allowed in C#?

  • Thread starter Thread starter Guest
  • Start date Start date
G

Guest

Hi,

Is null value for a class instance allowed in C#? for example:
MyClass obj = null;

If Not, how to initiate an instance with value 0? How to detect if an
instance is "newed" ? And how to pass a null value to a class constructor
whch has a object paramer can be 0?

In general, how C# handle a pointer with value 0;

Thanks
 
Hi there...

In your first sample ur definining an object (variable) but not creating it.
You know it's "newed" cuz obj != null
Yes it's possible to pass null to a constructor... for example

using System;

class Test {
static void Main() {
MyClass x = new MyClass(null);
Console.WriteLine("MyClass::Member is " + ((object) (x.Member !=
null ? "Not null" : "Null")).ToString());
Console.ReadLine();
}
}


class MyClass {
private object m_member;

public object Member {
get {return m_member;}
}

public MyClass(object arg) {
m_member = arg;
}
}


Regards,
 
Fei Li said:
Is null value for a class instance allowed in C#? for example:
MyClass obj = null;
Click to expand...

obj is a variable, not a class instance. null is effectively something
saying, "This value isn't a reference to a class instance at all. It's
a reference to no object."
If Not, how to initiate an instance with value 0?
Click to expand...

What do you mean "with value 0"?
How to detect if an instance is "newed" ?
Click to expand...

If a reference is non-null, it's a reference to an instance.
And how to pass a null value to a class constructor
whch has a object paramer can be 0?
Click to expand...

Just pass null.
In general, how C# handle a pointer with value 0;
Click to expand...

null is a special reference. You can possibly think of it as a pointer
with value 0, but it's better not to think in those terms - just think
of it as a reference meaning "No object".
 
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