When to use null

[Steven Blair]

Hi,

Here is a small example function. What I would like to know is when I
should be using null:

private bool MyTestFunc(string Message)
{
StreamWriter sw=null;
string str=null;

sw = new StreamWriter(FILE_PATH,true);

//Do some stuff with the SW
str = String.Format(@"{0}|{1}|",CLASS_NAME,message);
sw.WriteLine(str);
sw.Close();

//Not sure what to do here, but here is my guess
sw=null;
str=null;
//If I didnt set these to null, would that mean the
//The GC wouldnt clean these objects up?

return true;
}
Any help on this would be appreciated.

Regards,

Steven
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[Jon Skeet [C# MVP]]

Steven Blair <st**********@btinternet.com> wrote:

Here is a small example function. What I would like to know is when I
should be using null:

See http://blogs.msdn.com/csharpfaq/arch.../26/97229.aspx

What you *should* do is close your writer in a more reliable manner.
I'd also recommend only declaring variables at the point of first use.
I'd have written your method as:

void MyTestFunc (string message)
{
using (StreamWriter sw = new StreamWriter(FilePath, true))
{
sw.WriteLine ("{0}|{1}|", ClassName, message);
}
}

Differences:

o Constants follow MS naming conventions
o Parameter name follows MS naming conventions
o No need for the temporary string variable - the version of
WriteLine I use does the formatting anyway
o The StreamWriter is closed by the automatic call to Dispose
o String literal is now normal, rather than verbatim (as it
doesn't need to be verbatim)
o No declaration before use
o No unnecessary assignment to null
o No return value - on error, an exception will be thrown

Note that it still isn't thread-safe. Whether or not that's important
to you, I don't know.

--
Jon Skeet - <sk***@pobox.com>
http://www.pobox.com/~skeet
If replying to the group, please do not mail me too

[jhgjlk jkhg]

Ok, point taking. I will change my code to match what you have demontsrated.
But one of the points I was trying to get across was the use of strings.

Another small example:

void MyFunc()
{
string tmp=null;

tmp="Not very useful, only for testing";

//Do something with tmp

tmp=null // Is this neccessary?
}

Regards,

Steven

"Jon Skeet [C# MVP]" <sk***@pobox.com> wrote in message
news:MP************************@msnews.microsoft.c om...

Steven Blair <st**********@btinternet.com> wrote:

Here is a small example function. What I would like to know is when I
should be using null:

See http://blogs.msdn.com/csharpfaq/arch.../26/97229.aspx

What you *should* do is close your writer in a more reliable manner.
I'd also recommend only declaring variables at the point of first use.
I'd have written your method as:

void MyTestFunc (string message)
{
using (StreamWriter sw = new StreamWriter(FilePath, true))
{
sw.WriteLine ("{0}|{1}|", ClassName, message);
}
}

Differences:

o Constants follow MS naming conventions
o Parameter name follows MS naming conventions
o No need for the temporary string variable - the version of
WriteLine I use does the formatting anyway
o The StreamWriter is closed by the automatic call to Dispose
o String literal is now normal, rather than verbatim (as it
doesn't need to be verbatim)
o No declaration before use
o No unnecessary assignment to null
o No return value - on error, an exception will be thrown

Note that it still isn't thread-safe. Whether or not that's important
to you, I don't know.

--
Jon Skeet - <sk***@pobox.com>
http://www.pobox.com/~skeet
If replying to the group, please do not mail me too

[jhgjlk jkhg]

Sorry, last post is not needed now. Read the articel you supplied a link for
and that answers my secodn question :$

Regards,

Steven

"Jon Skeet [C# MVP]" <sk***@pobox.com> wrote in message
news:MP************************@msnews.microsoft.c om...

Steven Blair <st**********@btinternet.com> wrote:

Here is a small example function. What I would like to know is when I
should be using null:

See http://blogs.msdn.com/csharpfaq/arch.../26/97229.aspx

What you *should* do is close your writer in a more reliable manner.
I'd also recommend only declaring variables at the point of first use.
I'd have written your method as:

void MyTestFunc (string message)
{
using (StreamWriter sw = new StreamWriter(FilePath, true))
{
sw.WriteLine ("{0}|{1}|", ClassName, message);
}
}

Differences:

o Constants follow MS naming conventions
o Parameter name follows MS naming conventions
o No need for the temporary string variable - the version of
WriteLine I use does the formatting anyway
o The StreamWriter is closed by the automatic call to Dispose
o String literal is now normal, rather than verbatim (as it
doesn't need to be verbatim)
o No declaration before use
o No unnecessary assignment to null
o No return value - on error, an exception will be thrown

Note that it still isn't thread-safe. Whether or not that's important
to you, I don't know.

--
Jon Skeet - <sk***@pobox.com>
http://www.pobox.com/~skeet
If replying to the group, please do not mail me too