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From: phil@osiris.UUCP (Philip Kos)
Newsgroups: net.lang.c,net.micro.pc,net.unix
Subject: Re: C'mon, guys!
Message-ID: <835@osiris.UUCP>
Date: Thu, 19-Jun-86 09:15:36 EDT
Article-I.D.: osiris.835
Posted: Thu Jun 19 09:15:36 1986
Date-Received: Sat, 21-Jun-86 12:56:12 EDT
References: <811@bu-cs.UUCP>
Organization: Johns Hopkins Hospital
Lines: 64
Xref: watmath net.lang.c:9511 net.micro.pc:8764 net.unix:8288

Barry Shein writes:
> Guy Harris writes:
> >...sometimes I think pointers should be *subtracted* from C, since people
> >seem to get very confused about them...
> >...OK, maybe they're useful, and shouldn't be removed.  C classes should
> >spend *lots* more time on them than they are doing, though, given these
> >problems; better that people learn in class before they start writing code
> 
> Being as I teach a couple of C courses a year here at BU I thought I
> would comment on this, perhaps it would be of some use to language
> designers (or make them give up entirely!)
> 
> It's not 'C', I've had the same basic problems with students when
> teaching IBM assembler, PL/I and Pascal.
> 
> There seems to be some fundamental problem with distinguishing
> "the thing" from "the thing contained"*.....
> 
> 	-Barry Shein, Boston University

I'm sure that this is the problem with with many programmers, but not
all.  I just ran into a situation yesterday here at the Hospital where
one of our programmers was falsely attributing a bug to the C compiler
because the following declaration caused the program to die of a
segmentation violation:

	static char **ptrarray = {
		"",
		"str1",
		"str2",
		"etc."
	};

The programmer found that the alternate declaration

	static char *ptrarray[] = {
		"",
		"etc."
	};

ran just fine.  The confusion was compounded by the fact that this
programmer was taught in a supposedly reputable C class that *the two
declarations were always identical*.  I explained the situation in
which the two are effectively identical (formal parameter to a
function, natch) and the reason why the first just wouldn't work the
way it was intended, and things are OK now, but I'd like to point out
here that it's not just student C programmers who get confused about
pointers, and much more care needs to be taken on both ends of the
learning exchange process to ensure that the concept is transferred
completely and correctly.

(Of course there really *is* a bug in the compiler, since it let the
original declaration through without even a peep; it's just not the bug
imagined by the programmer.  For everyone's info, the compiler is cc on
OSx v3.1 [Pyramid Computer Corp.] and I have suggested that the company
be notified of this bug.  In the meantime, can anyone tell me whether
this is a known pcc bug, or is it specific to Pyramid's cc?)


Phil Kos			  ...!decvax!decuac
The Johns Hopkins Hospital                         > !aplcen!osiris!phil
Baltimore, MD			...!allegra!umcp-cs

"People say I'm crazy, dreaming my life away..."  - J. Lennon