| Re: Catching errors with widgets [message #856] |
Thu, 08 April 1993 11:18  |
landsman
Messages: 93
Registered: August 1991
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Member |
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In article <thompson.734276231@serts.gsfc.nasa.gov>, thompson@serts.gsfc.nasa.gov (William Thompson) writes...
> ian@gomez.jpl.nasa.gov (H. Ian Novack) writes:
>
>> I *can* get it to not blast out, but then, when I try to load another image
>> (of the right size), I get the following error message:
>
>> % COLOR_QUAN: Variable is undefined: <UNDEFINED>.
>> % Execution halted at ILOAD_EVENT </home/avdev/ian/idlpro/widget/id_load.pro(
>> 188)> (COLOR_QUAN).
>> % Called from XMANAGER </usr/local/idl/lib/widgets/xmanager.pro( 402)>.
>> % Called from ID </home/avdev/ian/idlpro/widget/id.pro( 289)>.
>> % Called from $MAIN$ .
>
>> Obviously, I can't tell which variable it's choking on.
>
> Why not? Try putting HELP statements just before the call to COLOR_QUAN to
> find out exactly what variables you're feeding it. I'd suggest putting a STOP
> command just before COLOR_QUAN, but I understand that this may cause problems
> with widgets in newer versions of IDL.
>
My experience is that the message
% COLOR_QUAN: Variable is undefined: <UNDEFINED>.
indicates an internal error in the IDL executable, and not a problem with the
Ian's IDL code. Note that ordinarily if one has an undefined variable, IDL
will display the name of the variable in the error message. The fact
that above error message does not give the name of the undefined variable shows
that it is not one of the variables that is being fed to COLOR_QUAN, but
rather an internal IDL error.
One known source of this type of the problem is the On_IOerror statement.
Very occasionally, ON_IOError appears to corrupt the IDL stack so that an
error can appear much later (usually in a widget program). I know RSI
is working on this although I don't know if they have a fix ready or the
next release.
Wayne Landsman landsman@stars.gsfc.nasa.gov
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