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Re: main or procedure [message #54628 is a reply to message #54627]

Wed, 20 June 2007 05:39

Conor
Messages: 138
Registered: February 2007

Senior Member

On Jun 20, 8:20 am, David Fanning <n...@dfanning.com> wrote:
> suj...@gmail.com writes:
>> When I .compile a procedure, it says,
>> You compiled a main program while inside a procedure. Returning.
>
>> And all the information before the compilation was lost.
>
>> How to fix it?
>
> You need to do two things: (1) Add more error handling
> to your code, so that when a program crashes it goes
> back to the main program level (ON_ERROR, 1), and (2)
> learn to type RETALL *immediately* when your program
> crashes, and certainly before you do any more compiling.
>
> 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.")

What's happening is the effects of variable scope. IDL has various
levels of "scope" for every variable it creates. When you initially
launch IDL, you are on the "MAIN" level. Everytime you run a program
or function, that program runs in its own separate scope, that is
below the "level" of the main level. Most importantly, it is entirely
separate from the main level with an independent set of variables.
So, if you have a variable named 'asdf' in your main level, and then
you launch a program, the program in question won't be able to access
that same 'asdf' variable, because your program runs in a different
scope. By default, the variables used in a program can't be used in
the main level, and vice-versa. Now, when a program encounters an
error and quits it returns you to the idl prompt, but it returns you
at the level of the program that had the error, not at the main
level. What this means is that when your program encounters an error
you won't immediately have access to the variables you declared
initially in the main level. In your case, another important point is
that when IDL is inside the scope of a program that had an error, and
that program is re-compiled, then IDL automatically returns you to the
main level and you automatically lose any variables that had existed
in the program's scope. That's what is happening to you. At some
point you are running a routine that gives an error. Then, you are
continuing to use the IDL command line, creating variables and doing
whatever it is you do. When you re-compile the program that had the
original error, IDL automatically returns you to the main level, and
all those variables you created go out of scope and are deleted. The
solution is quite simple. Just do what David pointed out. If you set
the ON_ERROR command inside your program like he noted, then idl will
return you to the main level when the program encounters an error,
rather than to the program level. This isn't the best solution during
development though, since returning to the main level means you lose
all your program variables and therefore you can't examine the state
of your program to see where the problem was. The other solution is
to simply type 'retall' before you resume working with the IDL command
line. 'retall' will return you to the main programming level, once
again giving you access to any variables you had created previously.

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[Message index]

		Re: main or procedure By: Carsten Lechte on Thu, 21 June 2007 12:06
		Re: main or procedure By: JD Smith on Wed, 20 June 2007 17:02
		Re: main or procedure By: JD Smith on Wed, 20 June 2007 16:36
		Re: main or procedure By: Carsten Lechte on Wed, 20 June 2007 13:13
		Re: main or procedure By: David Fanning on Wed, 20 June 2007 12:14
		Re: main or procedure By: Carsten Lechte on Wed, 20 June 2007 11:50
		Re: main or procedure By: Conor on Wed, 20 June 2007 11:54
		Re: main or procedure By: Paul Van Delst[1] on Wed, 20 June 2007 10:48
		Re: main or procedure By: Vince Hradil on Wed, 20 June 2007 09:47
		Re: main or procedure By: Carsten Lechte on Wed, 20 June 2007 09:12
		Re: main or procedure By: Carsten Lechte on Wed, 20 June 2007 09:03
		Re: main or procedure By: Conor on Wed, 20 June 2007 08:42
		Re: main or procedure By: David Fanning on Wed, 20 June 2007 07:56
		Re: main or procedure By: David Fanning on Wed, 20 June 2007 07:40
		Re: main or procedure By: Marshall Perrin on Wed, 20 June 2007 07:39
		Re: main or procedure By: Carsten Lechte on Wed, 20 June 2007 07:24
		Re: main or procedure By: David Fanning on Wed, 20 June 2007 07:00
		Re: main or procedure By: Carsten Lechte on Wed, 20 June 2007 06:07
		Re: main or procedure By: Conor on Wed, 20 June 2007 05:39
		Re: main or procedure By: David Fanning on Wed, 20 June 2007 05:20

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