| defsysv [message #7777] |
Wed, 15 January 1997 00:00  |
Jeff Hall
Messages: 7
Registered: September 1996
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Junior Member |
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Why does this work on the command line
IDL> '!jeff', 38
IDL> print, !jeff
when this doesn't work as a pro?
pro test
defsysv, '!jeff', 38
print, !jeff
end
Were are trying to utilize a user-defined
system variable to contain a handle value,
but there is this problem of being able to
define the system variable inside the
application. So far, we can only get it
to work on the command line, although after
the system variable has been defined on the
command line then the application works fine.
How do you use "defsysv" in a program?
Jeff
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| Re: defsysv [message #7898 is a reply to message #7777] |
Fri, 17 January 1997 00:00  |
Peter Mason
Messages: 145
Registered: June 1996
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Senior Member |
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On Wed, 15 Jan 1997, Jeff Hall wrote:
> Why does this work on the command line
>
> IDL> defsysv, '!jeff', 38
> IDL> print, !jeff
>
> when this doesn't work as a pro?
>
> pro test
> defsysv, '!jeff', 38
> print, !jeff
> end
I think this comes down to another strange "feature" in the IDL compiler:
It seems that IDL recognises system variables at COMPILATION time.
In your routine, !jeff is undefined at compilation time; this is
detected and IDL stops with an error message on the line "print, !jeff".
(!jeff only gets defined at runtime.)
A sort-of way out is to have a routine which defines system variables but
doesn't do anything else with them, and call it before any routine which uses
these system variables is compiled.
More simply, define all of your custom system variables at IDL startup (e.g.,
in a startup file). Then you can reassign their values in your programs
(e.g., !jeff=38).
Peter Mason
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