Path: utzoo!utgpu!water!watmath!clyde!rutgers!ucsd!ucbvax!hplabs!hpcea!hpfcdc!hpfclq!cunniff
From: cunniff@hpfclq.HP.COM (Ross Cunniff)
Newsgroups: comp.sys.amiga
Subject: Amiga programmer's hint $14
Message-ID: <4230019@hpfclq.HP.COM>
Date: 8 Feb 88 22:38:42 GMT
Organization: Hewlett-Packard
Lines: 50

For those of you who are using the Manx compiler (and perhaps for
those of you using 16-bit ints with the Lattice compiler), here's
a tip to help you avoid the Guru on machines with more that 512K.
This really happened to a friend of mine (we spent an entire WEEKEND
sorting this out; I would've seen it sooner, but Lattice promotes
bad programming practices :-< ).

	Q. What's wrong with this program?

	   #include <intuition/intuition.h>
	   struct IntuitionBase *IntuitionBase;
	   main()
	   {
	       IntuitionBase = (struct IntuitionBase *)
				OpenLibrary( "intuition.library", 33L );
	       JRandomIntuitionCall( .... );
	   }

	A. OpenLibrary is not declared explicitly as returning a
	   pointer.  This means that the compiler implicitly assumes
	   that it is returning an int.  On compilers which use
	   32-bit ints, this is no problem.  If you are using 16-bit
	   ints, this will Guru on a machine with $C000000 memory,
	   but *NOT* on a stock 512k Amiga.  Why?  Well, since
	   OpenLibrary returns an int (as far as the compiler knows),
	   the compiler just uses the *lower 16 bits* of the return value
	   when it stuffs it into IntuitionBase.  This is just ducky
	   on a 512K machine.  It's not so nice on a machine with more.
	   The solution?

	   #include <intuition/intuition.h>
	   struct IntuitionBase *IntuitionBase;
	   main()
	   {
	       struct Library
		   *OpenLibrary();	/* NOTE THE ADDITION OF THIS DECL! */

	       IntuitionBase = (struct IntuitionBase *)
				OpenLibrary( "intuition.library", 33L );
	       JRandomIntuitionCall( .... );
	   }

	   (I believe that the Manx compiler has a header file that
	   defines the return value of calls such as OpenLibrary; I
	   think it may be called <functions.h>).

				Ross Cunniff
				Hewlett-Packard System Sofware Operation
				...{ucbvax,hplabs}!hpda!cunniff
				cunniff%hplabs@hpda.ARPA