| Re: Help with pick menu widget code [message #12872] |
Thu, 17 September 1998 00:00  |
davidf
Messages: 2866
Registered: September 1996
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Senior Member |
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Rose Longfield (rmlongfield@my-dejanews.com) writes:
> Does this mean that I have to know before-hand that my module is going to
> cause an error? (Isn't this rather pessimistic) Or, I guess it is a good
> de-bugging technique, to be applied AFTER the program crashes. In this case I
> will try it out.
I use it as a debugging technique after I get over the shock
and dismay that my carefully crafted program didn't run perfectly. :-)
> I haven't had much luck with error handling in IDL. It usually causes me more
> trouble because I don't notice that an error has occurred.
This can be one of the big disadvantages of the CATCH mechanism
for catching errors. I once spent about three hours thinking IDL
had gone completely bonkers only to finally realize I had added
a silent CATCH to one of my modules. Needless to say, I don't
add any more silent CATCHes to *anything*. I write them like this:
CATCH, error
IF error NE 0 THEN BEGIN
Catch, /Cancel
ok = Dialog_Message(!Error_State.Msg)
Print, !Error_State.Msg
Widget_Control, event.top, Set_UValue=info, /No_Copy
RETURN
ENDIF
The Cancelling of the Catch keeps me from the infinite loop
that results when I incorporate errors in my error handling
code. Sigh... The Dialog_Message makes sure I know an error
occurred, because it is a modal dialog I *must* respond to.
The Print statement is there for me to refer to when I hit
the OK on the dialog before carefully reading the message
and I am trying to debug my code.
This CATCH will keep a widget program alive indefinitely,
but it also usually gives me enough notice to be able
to fix a problem. I suppose more bells and whistles and
flashing lights wouldn't hurt. My problem is that
I see this damn dialog so often that I have become
habituated to it and almost never *really* see it. :-)
Of course, occasionally, I want to disable this CATCH,
perhaps to find one of those "client application" errors.
Rather than add semi-colons to each of these lines (there
are occasionally more as I sometimes do *real* error handling
too), I modify the code like this:
;CATCH, error
error = 0
IF error NE 0 THEN BEGIN
Catch, /Cancel
ok = Dialog_Message(!Error_State.Msg)
Print, !Error_State.Msg
Widget_Control, event.top, Set_UValue=info, /No_Copy
RETURN
ENDIF
Cheers,
David
----------------------------------------------------------
David Fanning, Ph.D.
Fanning Software Consulting
E-Mail: davidf@dfanning.com
Phone: 970-221-0438, Toll-Free Book Orders: 1-888-461-0155
Coyote's Guide to IDL Programming: http://www.dfanning.com/
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