ALL 'try/catch/finally' NOT created equal?

[Ralph Krausse]

I created a try/catch/finally but when an expection is thrown, the
catch does not handle it... (I know this code is wrong, I want to
force the error for this example)


try
{
DataSet ds = new DataSet();
string strID = ds.Tables[0].Rows[0][0].ToString();
}
catch (SqlXmlException sqlxmlerr)
{
sqlxmlerr.ErrorStream.Position = 0;
StreamReader errreader = new StreamReader(sqlxmlerr.ErrorStream);
string err =errreader.ReadToEnd();
errreader.Close();
throw new Exception (err);
}
finally
{
}

This is a ASP.NET application and when the code hits 'string strID =
ds.Tables[0].Rows[0][0].ToString();' the exception is throw and the
result below is displayed in the browser.

*************

Cannot find table 0.
Description: An unhandled exception occurred during the execution of
the current web request. Please review the stack trace for more
information about the error and where it originated in the code.

Exception Details: System.IndexOutOfRangeException: Cannot find table
0.

Source Error:


Line 29: {
Line 30: DataSet ds = new DataSet();
Line 31: strID = ds.Tables[0].Rows[0][0].ToString();
Line 32: }
Line 33: catch (SqlXmlException sqlxmlerr)

*************


Now, if I replace SqlXmlException with System.Exception in the
catch(), the try/catch handles they way I thought and no browser error
happens, the code goes directly to my catch (during debugging, I made
sure).....

So my question.


Just because I have a try/catch doesn't mean it will ALWAYS catch
an exception. I guess I have proven this but wanted confirmation. So
how do I know what exception class to use? Where can I find this
information.

Thanks

Ralph Krausse
www.consiliumsoft.com
Use the START button? Then you need CSFastRunII...
A new kind of application launcher integrated in the taskbar!
ScreenShot - http://www.consiliumsoft.com/ScreenShot.jpg

 

[Shiva]

Hi,
Your code only catches SqlXmlException, but what is thrown is something
else; the code actually throws IndexOutOfRangeException. For this (& its
derivatives) to be caught, you have to add another catch block hadling this
specific exception:
try
{
}
catch (SqlXmlException sqlXmlErr)
{
}
catch (IndexOutOfRangeException idxErr)
{
}

To catch all exceptions in a single catch block, have a catch for the base
exception System.Exception, which is the root for all exception classes:

try
{
}
catch (Exception xcp)
{
}

Hope this helps.

I created a try/catch/finally but when an expection is thrown, the
catch does not handle it... (I know this code is wrong, I want to
force the error for this example)


try
{
DataSet ds = new DataSet();
string strID = ds.Tables[0].Rows[0][0].ToString();
}
catch (SqlXmlException sqlxmlerr)
{
sqlxmlerr.ErrorStream.Position = 0;
StreamReader errreader = new StreamReader(sqlxmlerr.ErrorStream);
string err =errreader.ReadToEnd();
errreader.Close();
throw new Exception (err);
}
finally
{
}

This is a ASP.NET application and when the code hits 'string strID =
ds.Tables[0].Rows[0][0].ToString();' the exception is throw and the
result below is displayed in the browser.

*************

Cannot find table 0.
Description: An unhandled exception occurred during the execution of
the current web request. Please review the stack trace for more
information about the error and where it originated in the code.

Exception Details: System.IndexOutOfRangeException: Cannot find table
0.

Source Error:


Line 29: {
Line 30: DataSet ds = new DataSet();
Line 31: strID = ds.Tables[0].Rows[0][0].ToString();
Line 32: }
Line 33: catch (SqlXmlException sqlxmlerr)

*************


Now, if I replace SqlXmlException with System.Exception in the
catch(), the try/catch handles they way I thought and no browser error
happens, the code goes directly to my catch (during debugging, I made
sure).....

So my question.


Just because I have a try/catch doesn't mean it will ALWAYS catch
an exception. I guess I have proven this but wanted confirmation. So
how do I know what exception class to use? Where can I find this
information.

Thanks

Ralph Krausse
www.consiliumsoft.com
Use the START button? Then you need CSFastRunII...
A new kind of application launcher integrated in the taskbar!
ScreenShot - http://www.consiliumsoft.com/ScreenShot.jpg

 

[Karl]

You can order your catches:
try{
}catch (SqlXmlException sqlxmlerr){
}catch (SqlException ex){
}finally{ }

Always go from most specific to least, if you switched those around and did:
try{
}catch (SqlException ex){
}catch (SqlXmlException exsqlxmlerr
}finally{ }

your 2nd catch would happen since your first one would swollow any
exceptions. As for knowing what code throws what exceptions, check the
documentation.

Cyrus from the C# team recently posted about something similar:
http://weblogs.asp.net/cyrusn/archive/2004/08/13/214006.aspx

Karl