| Automatic Compiliation of IDL Programs, Was: Lost Functions [message #10261] |
Tue, 04 November 1997 00:00  |
davidf
Messages: 2866
Registered: September 1996
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Senior Member |
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Martin Schultz (mgs@io.harvard.edu) makes some excellent
points when he writes:
> let me just add a little note on seperate files vs.
> "libraries", because I don't think this is mentioned
> in the IDL manuals: It seems as if the automatic
> compilation of IDL always compiles up to point where
> it finds the procedure or function with the same name
> as the filename.
Martin is mostly right about this, although the information
*is* found in the manuals. (I will admit that its reference
is a bit obscure for such an important point, however.)
I would like to elaborate on this a moment because you simply
would not believe the number of people I run into who
do not understand how programs get compiled. Many of these
people try to run IDL in the compile-link-run fashion of
the good ol' Fortran days. :-)
If you use the IDL executive command .Compile to compile
a file, all the program modules in the file get compiled.
(The executive command .Run can also be used this way,
although it confuses new IDL users because nothing actually
gets *run*.) To run the compiled programs, just use their
names on the IDL command line or in an IDL program.
But one of the wonderful features of IDL is the ability
to have your programs compiled *automatically* when they
are needed. This makes it possible to write IDL code that
is not cluttered up with a bunch of INCLUDE statements, etc.
You simply put all of your program files in some directory
that is on the IDL path and you don't have to worry whether
the files are pre-compiled or not when you write the next
IDL program that uses one of these commands.
But the key word here is "command". When you write a program
you are, in effect, creating another IDL command. The key rule
for getting your programs to compile automatically is to make
sure that the "command" module is the *last* program module
in a file that has the *same name* as the command you are
trying to build (with a ".pro" extension, of course).
For example, suppose I were trying to write an IDL program
or command named VIEW_IT. What I am trying to do is have
something happen when I type the name VIEW_IT at the IDL
command line or put that name in an IDL program. But VIEW_IT
might be a huge program with lots of subroutines, etc. I might
have routines called MAKE_BIG_WINDOW and GET_MY_DATA, etc, etc.
that I need to make my VIEW_IT program run.
What I should do is put the MAKE_BIG_WINDOW and GET_MY_DATA and
all the rest of the VIEW_IT utility routines in my file *in
front of* the VIEW_IT program module. In fact, VIEW_IT should
be the *last* module in the file. And I should name the file
"view_it.pro".
Now, when I type "view_it" at the IDL command line, IDL looks
for a file named "veiw_it.pro" (all lowercase letters on UNIX
file systems, no matter *how* you type it on the IDL command
line!). It compiles the program modules in that file *until*
it gets to the program module with the same name as the
file (which, don't you know, is the *last* program module :-),
at which point it stops compiling and *runs* that program
module automatically.
Now, it sometimes happens that a utility routine like
MAKE_BIG_WINDOW becomes a whole lot more useful to you
than it was before. In fact, you may want to use it
in a new program you are building called SEE_IT. If that
is the case, then take MAKE_BIG_WINDOW out of the VIEW_IT
code and put it in its own file called "make_big_window.pro".
It has now become another IDL command.
Automatic compilation doesn't solve *all* the problems
you might run into. (Hence, the Forward_Function command.)
But in my experience it solves a lot of them. And it sure
beats having to compile all of your program modules before
you can do anything in IDL. :-)
Cheers,
David
-----------------------------------------------------------
David Fanning, Ph.D.
Fanning Software Consulting
E-Mail: davidf@dfanning.com
Phone: 970-221-0438
Coyote's Guide to IDL Programming: http://www.dfanning.com/
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