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Path: utzoo!mnetor!seismo!lll-lcc!well!ewhac
From: ewhac@well.UUCP (Leo 'Bols Ewhac' Schwab)
Newsgroups: comp.sys.amiga
Subject: Re: Lock and FileLock
Message-ID: <2965@well.UUCP>
Date: Thu, 30-Apr-87 04:45:08 EDT
Article-I.D.: well.2965
Posted: Thu Apr 30 04:45:08 1987
Date-Received: Sat, 2-May-87 07:46:11 EDT
References: <6640@allegra.UUCP>
Reply-To: ewhac@well.UUCP (Leo 'Bols Ewhac' Schwab)
Organization: Whole Earth 'Lectronic Link, Sausalito, CA
Lines: 67
Summary: The Full and Compleat Story (I hope)

In article <6640@allegra.UUCP> dsf@allegra.UUCP (David Fox) writes:
>Furthermore, when I try to look at the
>field fd_Task of a lock, my system crashes.  Can anyone explain this to
>me?
>
>David Fox
>allegra!dsf
>
>P.S.  By look at, I mean that if I execute the statement
>task = lock->fl_Task, my system crashes.

	Phew.  Here we go again.  To all self-proclaimed Amiga Gurus reading
this, please let lesser-experienced Amiga programmers that you know in on
this information.  (In fact, someone could probably make some serious $$$
writing a book about all the "common" knowledge that isn't in the manuals.)

	Note:  People who have heard this a million times might want to hit
'n' now.

	Rule #1:  The DOS sucks.

	Rule #2:  The DOS was not written in C, it was written in a language
called BCPL (an acronym meaning, "British Compiler Programmers are Lousy"
(q.v. Rule #1)).  Because the languages are different, C's idea of a pointer
is different from BCPL's idea of a pointer.

	Rule #3:  Memory as we know it is addressed in byte-sized
increments.  BCPL, however, thinks memory is addressed in longword-sized
increments.  Therefore, a memory address in a BCPL pointer must be
multiplied by the size of a longword in bytes (i.e. four) to get a real
memory address.  Typically, this is done in C as follows:

	char *c_pointer;
	c_pointer = (char *) ((long) bcpl_pointer << 2);

	The various type casts may or may not be necessary, but it makes the
compiler shut up.

	Rule #4:  All AmigaDOS functions that claim to return a pointer in
fact return a BCPL pointer, commonly called a BPTR (meaning, "Braindamaged
PoinTeR").

	Rule #5:  Only those functions covered in the AmigaDOS Developer's
Manual are AmigaDOS functions.  All other functions in the ROM Kernel are
normal and well-behaved (e.g. GetMsg() does NOT return a BPTR (thank God)).

	David:  This was not meant to be insulting.  It's just that this has
been covered many times before, and things of this nature really ought to be
in the manuals in 36-point bold type.  As it is, people have to ask here.
Sigh.

	Hope this helps.  Spread this information far and wide; you will
help many novices this way.

P.S:	Sprinkle :-)'s where appropriate.

_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_
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