try...catch and local variables

[RickHodder]

I'm getting frustrated with using try...catch with local variables:

The code below wont compile in .NET 1.1: I get the following error: "Use of
unassigned local variable 'oProcessFileRe ader' "

Is there a way around this error?

<code>
private void Test(string sFileName)
{
StreamReader oProcessFileRea der;
try
{
oProcessFileRea der = File.OpenText(s FileName);
}
catch (Exception e)
{
MessageBox.Show ("Error: "+e.Message );
}
finally
{
if(oProcessFile Reader!=null)
oProcessFileRea der.Close();
}
}

</code>
--
Thanks
Rick Hodder

[Peter Bromberg [C# MVP]]

StreamReader oProcessFileRea der=null;

Now it's not unassigned.

Peter
--
Co-founder, Eggheadcafe.com developer portal:
http://www.eggheadcafe.com
UnBlog:
http://petesbloggerama.blogspot.com


"RickHodder " wrote:

I'm getting frustrated with using try...catch with local variables:

The code below wont compile in .NET 1.1: I get the following error: "Use of
unassigned local variable 'oProcessFileRe ader' "

Is there a way around this error?

<code>
private void Test(string sFileName)
{
StreamReader oProcessFileRea der;
try
{
oProcessFileRea der = File.OpenText(s FileName);
}
catch (Exception e)
{
MessageBox.Show ("Error: "+e.Message );
}
finally
{
if(oProcessFile Reader!=null)
oProcessFileRea der.Close();
}
}

</code>
--
Thanks
Rick Hodder

[Dustin Campbell]

I'm getting frustrated with using try...catch with local variables:

>
The code below wont compile in .NET 1.1: I get the following error:
"Use of unassigned local variable 'oProcessFileRe ader' "

Is there a way around this error?

Set oProcessFileRea der to null in your catch block.

Best Regards,
Dustin Campbell
Developer Express Inc.

[RickHodder]

Thanks Peter!

BTW, I really enjoy your blog.
--
Rick Hodder
"Peter Bromberg [C# MVP]" wrote:

StreamReader oProcessFileRea der=null;

Now it's not unassigned.

Peter
--
Co-founder, Eggheadcafe.com developer portal:
http://www.eggheadcafe.com
UnBlog:
http://petesbloggerama.blogspot.com


"RickHodder " wrote:

I'm getting frustrated with using try...catch with local variables:

The code below wont compile in .NET 1.1: I get the following error: "Use of
unassigned local variable 'oProcessFileRe ader' "

Is there a way around this error?

<code>
private void Test(string sFileName)
{
StreamReader oProcessFileRea der;
try
{
oProcessFileRea der = File.OpenText(s FileName);
}
catch (Exception e)
{
MessageBox.Show ("Error: "+e.Message );
}
finally
{
if(oProcessFile Reader!=null)
oProcessFileRea der.Close();
}
}

</code>
--
Thanks
Rick Hodder

[Mythran]

"RickHodder " <Ri********@dis cussions.micros oft.comwrote in message
news:F0******** *************** ***********@mic rosoft.com...

I'm getting frustrated with using try...catch with local variables:

The code below wont compile in .NET 1.1: I get the following error: "Use
of
unassigned local variable 'oProcessFileRe ader' "

Is there a way around this error?

<code>
private void Test(string sFileName)
{
StreamReader oProcessFileRea der;
try
{
oProcessFileRea der = File.OpenText(s FileName);
}
catch (Exception e)
{
MessageBox.Show ("Error: "+e.Message );
}
finally
{
if(oProcessFile Reader!=null)
oProcessFileRea der.Close();
}
}

</code>
--
Thanks
Rick Hodder

By just looking at the code and error, I see you are in fact not assigning
oProcessFileRea der before using it. Even though you are checking for null,
the compiler isn't smart enough to notice and it results in the error you
are getting. What you can do is simply modify your declaration to read:

StreamReader oProcessFileRea der = null;

and it should compile nicely (unless there are other errors in your code
that I'm over-looking.

Note: This is simply a compiler error and I'm not sure if you can turn off
this functionality. It exists to prevent you from doing something more
like:

StreamReader reader;
reader.ReadLine ();

Which is obviously bad, so the compiler warns/throws a tantrum when you try
to do something that even remotely resembles this...

HTH,
Mythran

[Sericinus hunter]

Mythran wrote:
....

Note: This is simply a compiler error and I'm not sure if you can turn
off this functionality. It exists to prevent you from doing something
more like:

StreamReader reader;
reader.ReadLine ();

Which is obviously bad, so the compiler warns/throws a tantrum when you
try to do something that even remotely resembles this...

Do you mean that |reader| in your example is null? I am not sure
if memory for local variable declarations is primed with zeros. Is it
somewhere in the language specifications?

[Marc Gravell]

I am not sure if memory for local variable

declarations is primed with zeros. Is it
somewhere in the language specifications?

ECMA-334, §12 "A variable shall be definitely assigned (§12.3) before its
value can be obtained."

So within the language, it is irrelevant (an implementation detail) whether
the variable is zero'd - as you cannot legally look to see. The CLR may
behave differently, but since this is a C# NG...

Marc

[Sericinus hunter]

Marc Gravell wrote:

>I am not sure if memory for local variable
declarations is primed with zeros. Is it
somewhere in the language specifications?

ECMA-334, §12 "A variable shall be definitely assigned (§12.3) before its
value can be obtained."

So within the language, it is irrelevant (an implementation detail) whether
the variable is zero'd - as you cannot legally look to see. The CLR may
behave differently, but since this is a C# NG...

Then, this is not a compiler error, contrary to what was suggested. Thanks.

[Mark R. Dawson]

Another way to write your code would be to use the "using" statement. It is
basically under the hood a try/finally statement which calls the Dispose
method on an object that implement IDisposable. If you want your catch
statement you will have to explicitly put that inside the using statment. So
your code:

private void Test(string sFileName)
{
StreamReader oProcessFileRea der;
try
{
oProcessFileRea der = File.OpenText(s FileName);
}
catch (Exception e)
{
MessageBox.Show ("Error: "+e.Message );
}
finally
{
if(oProcessFile Reader!=null)
oProcessFileRea der.Close();
}
}

would become (without the catch statement):

private void Test(string sFileName)
{
using(StreamRea der oProcessFileRea der = File.OpenText(s FileName))
{
//use the oProcessFileRea der
}

//here the stream has been disposed.
}

So even if an exception is thrown the resources are cleaned up, like in your
code, but with less typing :-).

Mark.
--
http://www.markdawson.org
"RickHodder " wrote:

I'm getting frustrated with using try...catch with local variables:

The code below wont compile in .NET 1.1: I get the following error: "Use of
unassigned local variable 'oProcessFileRe ader' "

Is there a way around this error?

<code>
private void Test(string sFileName)
{
StreamReader oProcessFileRea der;
try
{
oProcessFileRea der = File.OpenText(s FileName);
}
catch (Exception e)
{
MessageBox.Show ("Error: "+e.Message );
}
finally
{
if(oProcessFile Reader!=null)
oProcessFileRea der.Close();
}
}

</code>
--
Thanks
Rick Hodder

[Mythran]

"Sericinus hunter" <se*****@flash. netwrote in message
news:#T******** ******@TK2MSFTN GP02.phx.gbl...

Marc Gravell wrote:

>>I am not sure if memory for local variable
declaration s is primed with zeros. Is it
somewhere in the language specifications?

ECMA-334, §12 "A variable shall be definitely assigned (§12.3) before its
value can be obtained."

So within the language, it is irrelevant (an implementation detail)
whether the variable is zero'd - as you cannot legally look to see. The
CLR may behave differently, but since this is a C# NG...

Then, this is not a compiler error, contrary to what was suggested.
Thanks.

My apologies, it should read, "this is a compile* error" not compiler and
disregard the "I'm not sure if you can turn off this functionality", cause
obviously, you can't...

:)

HTH,
Mythran