troubles with finally statement and objects

[Chris]

Hi,

I am using the try catch finally block in many places in my code.

When a create an sqldatareader dr and try to close it in my
finally block I get the error: use of unsigned local variable.

dr.close();
works fine in the try but not in the finally.

How can I access my local objects in the finally without these errors?

thanks

Chris

[Nicholas Paldino [.NET/C# MVP]]

Chris,

You should be doing something like this:

// Delcare the reader.
SqlDataReader reader = null;

// Use the reader here.
try
{
// Create the reader.
reader = new SqlDataReader(. ..);

// Use the reader.
}
catch
{
}
finally
{
// Check the reader for null. If it is not, then
// dispose.
if (reader != null)
{
// Dispose of it.
((IDisposable) reader).Dispose ();
}
}

This should compile just fine. Chances are you missed the null
assignment to the variable declaration.

Hope this helps.

--
- Nicholas Paldino [.NET/C# MVP]
- mv*@spam.guard. caspershouse.co m

"Chris" <Ch***@discussi ons.microsoft.c om> wrote in message
news:FF******** *************** ***********@mic rosoft.com...

Hi,

I am using the try catch finally block in many places in my code.

When a create an sqldatareader dr and try to close it in my
finally block I get the error: use of unsigned local variable.

dr.close();
works fine in the try but not in the finally.

How can I access my local objects in the finally without these errors?

thanks

Chris

[Siva M]

Looks like the variable dr is declared inside try block - dr is only local
to try {} and not accessible in finally block. For your case, decalre dr
outside the try block so that you can access it in both try as well as
finally blocks.

"Chris" <Ch***@discussi ons.microsoft.c om> wrote in message
news:FF******** *************** ***********@mic rosoft.com...
Hi,

I am using the try catch finally block in many places in my code.

When a create an sqldatareader dr and try to close it in my
finally block I get the error: use of unsigned local variable.

dr.close();
works fine in the try but not in the finally.

How can I access my local objects in the finally without these errors?

thanks

Chris

[Nick Malik [Microsoft]]

"Chris" <Ch***@discussi ons.microsoft.c om> wrote in message
news:FF******** *************** ***********@mic rosoft.com...

Hi,

I am using the try catch finally block in many places in my code.

When a create an sqldatareader dr and try to close it in my
finally block I get the error: use of unsigned local variable.

dr.close();
works fine in the try but not in the finally.

How can I access my local objects in the finally without these errors?

Hi Chris,

In addition to the excellent answers given so far, there is another
construct of C# that you may not be aware of.

You are clearly being a good citizen and cleaning up the data reader during
error handling. However, C# has a pretty nice construct that will call the
..Dispose method for you... it is called 'using'

I snatched a bad example of using the Data Reader object from a random site
and rewrote it to use the 'using' statement, here:

SqlDataReader data;
using (data = command.Execute Reader(CommandB ehavior.CloseCo nnection))
{
while( data.Read() )

{
Console.WriteLi ne("Company Name " +
data.GetString( data.GetOrdinal ("CompanyName") );

}
} // automatically calls data.Dispose();

Here is the spec page in the MSDN. It's a very cool capability of the
language, and reduces your code brilliantly.
Note: you still need a try-catch-finally, but you won't need to close the
data reader, because leaving that block of 'using' code, FOR ANY REASON,
will call Dispose for you.

http://msdn.microsoft.com/library/de...pspec_8_13.asp
--
--- Nick Malik [Microsoft]
MCSD, CFPS, Certified Scrummaster
http://blogs.msdn.com/nickmalik

Disclaimer: Opinions expressed in this forum are my own, and not
representative of my employer.
I do not answer questions on behalf of my employer. I'm just a
programmer helping programmers.
--

[Jon Skeet [C# MVP]]

Nick Malik [Microsoft] <ni*******@hotm ail.nospam.com> wrote:

I snatched a bad example of using the Data Reader object from a random site
and rewrote it to use the 'using' statement, here:

SqlDataReader data;
using (data = command.Execute Reader(CommandB ehavior.CloseCo nnection))
{
while( data.Read() )

{
Console.WriteLi ne("Company Name " +
data.GetString( data.GetOrdinal ("CompanyName") );

}
} // automatically calls data.Dispose();
That would be better written IMO as:

using (SqlDataReader data = command.Execute Reader
(CommandBehavio r.CloseConnecti on))
{
while( data.Read() )
{
Console.WriteLi ne("Company Name " +
data.GetString( data.GetOrdinal ("CompanyName") );

}
} // automatically calls data.Dispose();

There's no point in letting the variable have a wider scope than the
using block, and it's better to give it the smallest scope it needs.
Here is the spec page in the MSDN. It's a very cool capability of the
language, and reduces your code brilliantly.

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

[Nick Malik [Microsoft]]

"Jon Skeet [C# MVP]" <sk***@pobox.co m> wrote in message
news:MP******** *************** *@msnews.micros oft.com...

That would be better written IMO as:

using (SqlDataReader data = command.Execute Reader
(CommandBehavio r.CloseConnecti on))
{
while( data.Read() )
{
Console.WriteLi ne("Company Name " +
data.GetString( data.GetOrdinal ("CompanyName") );

}
} // automatically calls data.Dispose();

There's no point in letting the variable have a wider scope than the
using block, and it's better to give it the smallest scope it needs.

Thanks, Jon. That's what I get for rewriting something I snatch off of a
web site. I agree with your change completely.

--
--- Nick Malik [Microsoft]
MCSD, CFPS, Certified Scrummaster
http://blogs.msdn.com/nickmalik

Disclaimer: Opinions expressed in this forum are my own, and not
representative of my employer.
I do not answer questions on behalf of my employer. I'm just a
programmer helping programmers.
--

[Scott Roberts]

"Nick Malik [Microsoft]" <ni*******@hotm ail.nospam.com> wrote in message
news:_t******** ************@co mcast.com...

SqlDataReader data;
using (data = command.Execute Reader(CommandB ehavior.CloseCo nnection))
{
while( data.Read() )

{
Console.WriteLi ne("Company Name " +
data.GetString( data.GetOrdinal ("CompanyName") );

}
} // automatically calls data.Dispose();

Why don't I like that? Is it because it's new and I'm not used to it? I want
to see the call to Close() in there somewhere. Am I becoming old and set in
my ways?

[Jon Skeet [C# MVP]]

Scott Roberts <sc***********@ no-spam.intelebill .com> wrote:

<snip using statement example>

Why don't I like that? Is it because it's new and I'm not used to it? I want
to see the call to Close() in there somewhere. Am I becoming old and set in
my ways?

I hope it's just because you're not used to it. The "using" statement
is one of the top things I prefer about C# to Java, despite it only
being syntactic sugar. It makes things *much* more readable (admittedly
only when you know what the using statement does!), and makes it far
simpler to "get it right" when it comes to disposing of things.

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

[Scott Roberts]

"Jon Skeet [C# MVP]" <sk***@pobox.co m> wrote in message
news:MP******** *************** *@msnews.micros oft.com...

It makes things *much* more readable (admittedly
only when you know what the using statement does!), and makes it far
simpler to "get it right" when it comes to disposing of things.

I know what "using" does, so I don't think that's it. I don't know what
happens in Dispose() of every single class in the .NET library. Perhaps
that's it. I'd like to see Close() then Dispose() to be sure Close()
actually happened. Perhaps this is paranoia on my part. If so, hopefully
I'll get over it.

[Jon Skeet [C# MVP]]

Scott Roberts <sc***********@ no-spam.intelebill .com> wrote:

It makes things *much* more readable (admittedly
only when you know what the using statement does!), and makes it far
simpler to "get it right" when it comes to disposing of things.

I know what "using" does, so I don't think that's it. I don't know what
happens in Dispose() of every single class in the .NET library. Perhaps
that's it. I'd like to see Close() then Dispose() to be sure Close()
actually happened. Perhaps this is paranoia on my part. If so, hopefully
I'll get over it.

If Dispose() doesn't correctly deal with a resource, then it's a bug -
but you could just as easily have the bug in Close as in Dispose. Note
that making sure you call both Close *and* Dispose involves having
*two* finally blocks, making the code even harder to read :)

As you say, hopefully you'll get over it :)

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