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From: rharwood@east.pima.edu
Newsgroups: comp.lang.ada
Subject: Re: Command line arguments
Message-ID: <1991Apr29.224029.1@east.pima.edu>
Date: 30 Apr 91 05:40:29 GMT
Article-I.D.: east.1991Apr29.224029.1
References: <91113.165139TAINT021@ysub.ysu.edu> <1991Apr25.143711.11311@ecst.csuchico.edu> <3275@enea.se>
List-Id: <comp.lang.ada>

In article <3275@enea.se>, sommar@enea.se (Erland Sommarskog) writes:
> Undoubtedly it would be pleasant if all Ada compilers on
> Unix were interchangeable on argv/argc, but that something
> like a POSIX binding not Ada 9X.
> 
> Since you retrieve the arguments differently in different OSs,
> reading the command line is something which by definition is
> not portable(*) so it can't be in the language. Remember that 
> the command-line interface itself is OS dependent.
> 
> (*) Yes, I know that argc/argv is commonly available with C
> implementations. But if you're going to get the command-line
> interface right in, say, VMS, you better use the CLI$ routines.

Erland, I agree 100%.  Here's perhaps some more "justification".

Perhaps the "correct" way for portability would be to write a package for EACH
PROGRAM (or system) that has functions which return the possible values of
switches and other command line "entries", like the following parameters for a
PC-based file DUMP routine I recently wrote:

  type bases is (hex, ascii, octal);
  function address_format return bases;
  function file_to_dump return string;

Then your "main" routine calls these functions, no matter what the external
environment is.  NOW comes the "non-portable" interface, where the actual
BODIES of those functions above must call the OS-specific routines to determine
the command line arguments.  It would conceptually be possible to write two
external interface routines:

(1) one which works under the "unit test" mode and runs on the "host" system
such as the VAX or PC-compatible

(2) another which runs only on the target hardware, perhaps an embedded 80186
or 1750A machine.

Ada is NOT the first language where information hiding has advantages...  We
must THINK in terms of portability and encapsulation during DESIGN. At CODE
time is too late!  <"plop-plop"... stepping of off soap box>

Ray
-----
Ray Harwood           |Data Basix           |Associate Faculty,    
Voice: (602)721-1988  |PO Box 18324         |   Pima Community College
FAX:   (602)721-7240  |Tucson, AZ 85731     |Instructor in Ada and Pascal
CompuServe: 76645,1370|AppleLink: DATA.BASIX|Internet: rharwood@east.pima.edu