[3.0/LINQ] Please clarify

[vkkishore_s]

hi friends

can any body tell me what is the purpose of below syntax in c#

list<classname>classobject=null;

if any body have an idea please share with me.if possible plz give me an example.

Thanks in advance

Regards
Kishore

[syntaxeater]

That isn't linq - just a declaration.

You end up with a variable named classobject capable of pointing to an instance of a Generic.List containing classname objects. The "= null" however, is redundant.

[techgnome]

If you are familiar with VB.NET, it's equivilent to this:
Dim classobject as List(Of classname) = Nothing

syntax - No one said it was LINQ. the LINQ in the subject is the default for when you select FW3 from the C# forum.... I've complained about that a number oftimes (as LINQ is more than jsut C#).... but because of the hacks & changes, it ain't gonna change any time soon, if ever.

-tg

[syntaxeater]

syntax - No one said it was LINQ. the LINQ in the subject is the default for when you select FW3 from the C# forum.... I've complained about that a number oftimes (as LINQ is more than jsut C#).... but because of the hacks & changes, it ain't gonna change any time soon, if ever.

Ahhh, makes sense. My mistake, was not aware.

[jmcilhinney]

The "= null" however, is redundant.

Not so, or at least not necessarily so. If you do this:

private void Form1_Load(object sender, EventArgs e)
{
    List<object> list;
 
    this.DoSomething(ref list);
}
 
private void DoSomething(ref List<object> list)
{
    // ...
}

you'll get a compilation error "Use of unassigned local variable" but if you do this:

private void Form1_Load(object sender, EventArgs e)
{
    List<object> list = null;
 
    this.DoSomething(ref list);
}
 
private void DoSomething(ref List<object> list)
{
    // ...
}

you won't. By assigning null explicitly you are telling the compiler that you specifically want the variable to be null and you'll take responsibility for making sure that a NullReferenceException doesn't occur. By refusing to compile without the assignment the compiler ensures that you haven't just forgotten to assign a value.

[drattansingh]

This is not an answer to the question but rather another question under the same topic. If i have the following:

int x=4;

Then I create a variable called x, assign 4 bytes of memory since its int and allocate 4 to this portion of memory. However if i have:

int x=null;

As far as i know NULL means nothing and its either a data type of a keyword in most languages. So is 4 bytes of memory allocated in this case also?


Jennifer.

[jmcilhinney]

This is not an answer to the question but rather another question under the same topic. If i have the following:

int x=4;

Then I create a variable called x, assign 4 bytes of memory since its int and allocate 4 to this portion of memory. However if i have:

int x=null;

As far as i know NULL means nothing and its either a data type of a keyword in most languages. So is 4 bytes of memory allocated in this case also?


Jennifer.

It must be because the variable is type int and int is ALWAYS 32-bits wide. You are reading that as one statement because in C# it is but when the C# code is compiled to MSIL the creation of the variable is completely separate to the assignment. Consider this:

int x = null;
x = int.MaxValue;

How could the second line be executed if the first line didn't create a 32-bit variable?

The size of EVERY variable is determined by its TYPE, not its VALUE. The value is COMPLETELY irrelevant to the amount of space a variable occupies. ALL reference type variables occupy 32 bits on a 32-bit system because that's the amount of space a memory address requires. The size of a value type variable depends on the cumulative size of its members. Variables of this type:

public struct MyStruct
{
    string str;
    long lng;
}

will ALWAYS be 96 bits in size because a string variable is 32-bit and a long is 64-bit.