| Re: Simple question regarding CATCH,/CANCEL [message #72667] |
Tue, 28 September 2010 15:51 |
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Paul Van Delst[1]
Messages: 1157
Registered: April 2002
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Senior Member |
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David Fanning wrote:
> mgalloy writes:
>
>> In my experience, typical use of CATCH, /CANCEL is like:
>>
>> catch, error
>> if (error ne 0L) then begin
>> catch, /cancel
>> ... handle error ..
>> endif
>>
>> The CATCH, /CANCEL is used to turn off CATCH-ing errors in the "...
>> handle error ..." part -- this would cause a recursive loop in the error
>> handling code if an error was encountered in the error handling code itself.
>
> Outside of debugging code, this is about the only way I
> ever use it, too.
O.k., good to know.
I can now delete all the superfluous "CATCH,/CANCEL"'s in my code.
> I could see using it inside a function that had an
> ON_ERROR, 2 condition that I wanted to temporarily
> override to catch an anticipated error in the function.
> When I got past the danger spot I might cancel the
> Catch so that the normal RETURN from the function was
> in effect.
Hmm. I no longer use ON_ERROR because CATCH seems to, well, catch everything error-wise.
I do the following for temporary overrides via a ubiquitous Debug keyword:
IF ( KEYWORD_SET(Debug) ) THEN BEGIN
MESSAGE, '--> Entered.', /INFORMATIONAL
MsgSwitch = 0
ENDIF ELSE BEGIN
CATCH, Error_Status
IF ( Error_Status NE 0 ) THEN BEGIN
CATCH, /CANCEL
MESSAGE, !ERROR_STATE.MSG
ENDIF
MsgSwitch = 1
ENDELSE
(with similar for functions)
All my subsequent error message output does something like
MESSAGE, 'an error has occurred', NONAME=MsgSwitch, NOPRINT=MsgSwitch
If I set Debug, the error msg is output and execution stops so I can interactively inquire what happened.
If I don't set Debug, the error msg is output and the error handler takes over and the error bubbles up the call chain.
I think I'm doing something twice here that doesn't need doing.... or I'm leaving something out... can't remember which.
But it works pretty well. :o)
cheers,
paulv
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| Re: Simple question regarding CATCH,/CANCEL [message #72668 is a reply to message #72667] |
Tue, 28 September 2010 15:18  |
David Fanning
Messages: 11724
Registered: August 2001
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Senior Member |
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mgalloy writes:
> In my experience, typical use of CATCH, /CANCEL is like:
>
> catch, error
> if (error ne 0L) then begin
> catch, /cancel
> ... handle error ..
> endif
>
> The CATCH, /CANCEL is used to turn off CATCH-ing errors in the "...
> handle error ..." part -- this would cause a recursive loop in the error
> handling code if an error was encountered in the error handling code itself.
Outside of debugging code, this is about the only way I
ever use it, too.
I could see using it inside a function that had an
ON_ERROR, 2 condition that I wanted to temporarily
override to catch an anticipated error in the function.
When I got past the danger spot I might cancel the
Catch so that the normal RETURN from the function was
in effect.
Cheers,
David
--
David Fanning, Ph.D.
Fanning Software Consulting, Inc.
Coyote's Guide to IDL Programming: http://www.dfanning.com/
Sepore ma de ni thui. ("Perhaps thou speakest truth.")
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| Re: Simple question regarding CATCH,/CANCEL [message #72669 is a reply to message #72668] |
Tue, 28 September 2010 14:57 |
Michael Galloy
Messages: 1114
Registered: April 2006
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Senior Member |
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On 9/28/10 3:28 PM, Paul van Delst wrote:
> Hello,
>
> I use CATCH error handling in just about all of my IDL procedures/functions.
>
> If no error occurs, do I need a
> CATCH, /CANCEL
> at the end of the pro/func? Or does exiting the pro/func cancel the error handling that was established on entry
> automatically?
>
> The documentation doesn't explicit state what happens, although the example does *not* have a "CATCH,/CANCEL" before the
> END (I also recall reading a post on this newsgroup stating that it was not necessary to CANCEL and error handler for
> normal termination).
In my experience, typical use of CATCH, /CANCEL is like:
catch, error
if (error ne 0L) then begin
catch, /cancel
... handle error ..
endif
The CATCH, /CANCEL is used to turn off CATCH-ing errors in the "...
handle error ..." part -- this would cause a recursive loop in the error
handling code if an error was encountered in the error handling code itself.
Mike
--
www.michaelgalloy.com
Research Mathematician
Tech-X Corporation
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