Re: Command line arguments

[sampson@cod.NOSC.MIL (Charles H. Sampson)]

In article <1991Apr30.135735.1211@iplmail.orl.mmc.com> sag@iplmail.orl.mmc.com (Steve Gabrilowitz) writes:
>       ... if Ada had some construct defined as a part of the language
>which would retrieve the commmand line parameters nothing would prevent
>the compiler writers from implementing whatever it was on VMS by internally
>calling the appropriate CLI$ functions - and isn't that part of what Ada
>is all about, providing a programming environment which is uniform and
>consistent over different platforms? 
>
>The only problem I see with putting access to the command line into the
>Ada language is how it would be handled on embedded real time systems where
>the OS doesn't provide any mechanism for getting at the command line -
>indeed, there isn't even a command line to get at ;-)
>
>Perhaps this could best be handled by providing a recommended "standard"
>for getting the command line in Chapter 13?

     This issue was discussed a few months ago and I'll repeat the same
point I tried to make then.  Suppose there were a standard Ada technique
for accessing command line parameters.  What would it gain you?  You
could get at the parameters, but they would be different on different
operating systems, so the code to process those parameters would not be
transportable.

     In saying this I assume that you want the parameters in the VMS
version of your program to be VMS-like, and in the UNIX version to be
UNIX-like.  If this assumption is wrong we can argue about it, but the
issue is then user interface, not Ada.

     I've now directed the implementation of several small multi-platform
programs written in Ada and the approach that I've used is one suggested
by another responder: The information obtained from the command line
parameters is abstracted in a package specification; that package's body
is rewritten for each environment.  One of these programs was ported to
an environment that does not have command line parameters and the package
body in this case implemented a set of hierarchical menus to obtain the
required information.

                             Charlie