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From: ok@goanna.cs.rmit.EDU.AU (Richard A. O'Keefe)
Subject: Re: Coding Standards
Date: 1996/05/17
Message-ID: <4nh3n7$55g@goanna.cs.rmit.EDU.AU>#1/1
X-Deja-AN: 155276532
references: <9605151401.AA04364@most> <319B286E.3B2E@lmtas.lmco.com>
organization: Comp Sci, RMIT, Melbourne, Australia
nntp-posting-user: ok
newsgroups: comp.lang.ada
Date: 1996-05-17T00:00:00+00:00
List-Id: <comp.lang.ada>


I liked initialised variables a lot, but I get to see rather more
student code than my nerves can really cope with, and the 300th
time you see

	n: Integer := 1;		int n = 0;
	<two pages>			<three pages>
	while n <= max loop		while (n+1 <= max) {
	    <one page>			    { <one page>
	    n := n+1;			    ++n;
	end loop;			   }

(Yes, the C is strangely indented, that's what I see.)
you realise "it is important to group related things together",
and "being able to move the first assignment up into the declarative
region tempts many beginners to do it when they shouldn't".

I've been looking for some guidelines, and I think that these are good:

    - constants MUST be initialised where they are declared

	X: constant Integer := ....;
	int const X = ...;

	(of course this doesn't apply to Ada deferred constants; give me
	credit for some sense.)

    - ALL variables must be initialised before they are used,
	WHETHER THE LANGUAGE WILL INITIALISE THEM OR NOT.

	This means I don't _care_ what Ada initialises pointers to,
	and I don't care what C initialises top-level variables to
	either.

    - other things being equal, the initialisation of a variable
      should be as late as possible.

    - other things being equal, the initialisation of a variable
      should be as close to its uses in the text as possible,
      so that when looking at the uses, the initialisation is
      visible.

I understand why Ada initialises pointers to null, and I wouldn't want
that changed, but if I want to check that a variable is properly
initialised, I want to _see_ an initialisation.

I would also like to point out that in this year's C class, the second
biggest cause of run-time errors (after the obvious biggie: design errors)
was uninitialised variables.  The lucky students were the ones where this
resulted in a NULL pointers that were caught by the hardware.
Students keep on telling me their program "works" when they really mean
that Turbo C failed to notice the problem most of the time.  (They are
actually required to compile their programs on a SPARC/Solaris system,
which is when they start complaining that 'cc' or 'gcc' is "broken".)

For teaching purposes, at any rate, I am 
 *for* any tool that will help to detect uninitialised variable use
 *against* any "solution" to the problem that requires programmer
     intervention; if the students were savvy enough to use such a
     solution, they wouldn't need it so much.

For developing large long-lived software systems where performance is
an issue, the tradeoffs are different.
-- 
Fifty years of programming language research, and we end up with C++ ???
Richard A. O'Keefe; http://www.cs.rmit.edu.au/~ok; RMIT Comp.Sci.