From:	CSBVAX::MRGATE!@KL.SRI.Com,@wiscvm.wisc.edu:LANGFORD@VCUVAX.BITNET@SMTP  5-NOV-1987 12:08
To:	EVERHART
Subj:	RE: Signalling VMS conditions from Pascal programs

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Date:     Wed, 4 Nov 87 15:53 EST
From:     <LANGFORD%VCUVAX.BITNET@wiscvm.wisc.edu> (Bob Langford)
Subject:  RE: Signalling VMS conditions from Pascal programs
To:       info-vax@kl.sri.com
X-Original-To:  info-vax@kl.sri.com, LANGFORD

In response to:

>FROM: Bill Costa, University Computing <W_COSTA@UNHH>
>Subject:      TIP ON: Using the message facility with Pascal
>
>    I wanted to use the Message Utility with my VAX Pascal programs.
>    Unfortunately there does not appear to be any way of declaring external
>    constants in VAX Pascal.  This means that you would have to hand-code
>    the "condition codes" values found in the Message Utility listing of
>    your message file into your Pascal program.  Uck! However, I think I've
>    worked out what I think is a better way. The trick is to declare some
>    [EXTERNAL] variables with the same name as the condition code symbols
>    that you defined in your message file.  These variables will contain
>    nothing (and thus waste a little space), but they will be recognized by
>    the linker as being the same as the symbols defined in the message OBJ
>    file.
>
>    **NOW** - I have a question for the VMS/VAX Pascal *gurus* out there.
>    Could you give me a hint (in other words show me) how to declare
>    LIB$SIGNAL in VAX Pascal so I can pass FAO arguments?

I've been doing this for some time, and include the following Pascal
example (heavily chopped to pieces to leave just the good stuff) to show
how I do it.  Hope this helps!

                 Bob Langford,
                 Medical College of Virginia / Virginia Commonwealth Univ.
                 LANGFORD @ VCUVAX  (Bitnet)
---------------------------
{ Pascal fragments to show how I signal errors from Pascal programs. }

[inherit('sys$library:starlet',         { System services and RMS }
         'sys$library:rtl')]       { RTL routines including LIB$SIGNAL
                                     (a homegrown file) }
program DETAB (input, output);

var                     { Error messages. }
    DETAB__ERROPEINP, DETAB__ERROPEOUT : [external, value] integer;
    inStat : integer;
{+++
The [external, value] attributes are new in Pascal, but they do exactly
what you want/need in this case:  tell the compiler that this is a global
symbol defined in another module, whose address should be used as an integer.
It could also be defined as UNSIGNED, if you declare LIB$SIGNAL that way,
but all the routines in STARLET.PAS return INTEGERs (when they should give
UNSIGNED, according to the System Services manual).
---}

begin

lib$signal (DETAB__ERROPEINP, 1, %stdescr FileSpec, inStat);
{+++ This call actually signals two condition codes: DETAB__ERROPEINP and
     the code in "inStat" (in this case, an RMS condition code).  The
     DETAB__ERROPEINP signal has 1 argument, "FileSpec", which is a
     varying length string (varying [100] of char).
---}
end.    { main }

---------------------------
Here's the declaration of LIB$SIGNAL used above (from SYS$LIBRARY:RTL.PAS,
a file we had to write ourselves):

[EXTERNAL, ASYNCHRONOUS]
function LIB$SIGNAL (
  %immed cond : [readonly] integer := %immed 1;
  %immed params : [readonly,list,unsafe] integer := %immed 0
        ) : integer; external;

---------------------------
Here's the Message utility input file:

        .title  DETAB program error messages
        .ident  'V 1.0'
        .facility       DETAB, 1000 /prefix=DETAB__

        .severity       ERROR
ErrOpeInp       "Error opening input file, `!AS'"/fao=1
ErrOpeOut       "Error opening output file, `!AS'"/fao=1

        .end

---------------------------
Here's how I compile/link it all:

$ pascal mainpgm.pas
$ message error_codes.msg
$ link/notraceback mainpgm.obj,error_codes.obj

(naturally, system-wide condition values are automatically found by the
 linker, and no .OBJ file need be given for them.)