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From: lambert@spectrum.eecs.unsw.oz (Tim Lambert)
Newsgroups: comp.sys.apollo
Subject: Re: bitmap and image conversion programs
Message-ID: <LAMBERT.90Apr9190356@nankeen.spectrum.cs.unsw.oz.au>
Date: 9 Apr 90 09:03:55 GMT
References: <1990Apr8.161841.14435@bath.ac.uk>
Sender: news@usage.csd.unsw.oz
Organization: none
Lines: 40
In-reply-to: @gdt.bath.ac.uk's message of 8 Apr 90 16:18:41 GMT

In article <1990Apr8.161841.14435@bath.ac.uk> @gdt.bath.ac.uk writes:

   The graphics programs made available by ROQUE OLIVEIRA
   (oliveria@caen.engin.umich.edu) at freebie.engin.umich.edu
   contain gpr calls of the following type...

	  status_$t   status;

	  gpr_$***(...,...,&status)

   Why is status passed as &status?

   I'm using SR9.7 (still, maybe this summer we'll "upgrade" :-)),
   Apollo CC, Rev 5.50

Because he's using
#include <apollo/gpr.h>
and not
#include /sys/ins/gpr.ins.c

Compare /sys/ins/gpr.ins.c

   std_$call void   gpr_$terminate ();

with /usr/include/apollo/gpr.h

   extern void gpr_$terminate (
       boolean            & delete_disp,    /*whether to delete dm frame */
       status_$t          * status);        /*returned status */

The std_$call makes all the arguments get passed by reference (so when you
say just status, the address gets passed), whereas the function prototype
says that status is passed by value so you need the more natural &status.

The function prototype is preferable since the types of arguments get
checked, but I don't think this exists in 9.7

   [ I've got the recent bgc.pas converted to bgc.c if anyone is interested ]

Wow! Does it work under 9.7? :-)