Path: utzoo!utgpu!jarvis.csri.toronto.edu!rutgers!tut.cis.ohio-state.edu!ucbvax!decwrl!decvax!ima!haddock!karl
From: karl@haddock.ima.isc.com (Karl Heuer)
Newsgroups: comp.lang.c
Subject: Re: Another silly question
Message-ID: <13415@haddock.ima.isc.com>
Date: 26 May 89 03:40:21 GMT
References: <17812@cup.portal.com> <607@kl-cs.UUCP> <749@mccc.UUCP> <13269@haddock.ima.isc.com> <96@elf115.uu.net>
Reply-To: karl@haddock.ima.isc.com (Karl Heuer)
Organization: Interactive Systems, Boston
Lines: 34

In article <96@elf115.uu.net> rec@elf115.uu.net (Roger Critchlow) writes:
>In <13269@haddock.ima.isc.com> karl@haddock.ima.isc.com (Karl Heuer) writes:
>>In article <105998@sun.Eng.Sun.COM> jamesa@arabian.Sun.COM (James D. Allen) writes:
>>>Any idea why this [enclosing in a struct] wasn't done for jmp_buf's?
>>
>>Originally?  Probably shortsightedness.
>
>I believe that struct's were still second class objects when
>jmp_buf was first declared.

But arrays were (and still are) third-class objects.  A struct would still
have been the better choice.

(Or do you mean to suggest that structs didn't exist at all?  I bet if you go
back that far, typedef didn't exist either.)

>The declaration of a jmp_buf as an array means that the jmp_buf
>is passed by reference instead of by value.  This is essential
>to many implementations of setjmp().

Of course it has to be passed by reference; the function needs to write in it,
after all.  But what *should* have been done was to typedef jmp_buf as a
struct, and use "&" explicitly.  That's what the rest of the library uses when
call by reference is required.

>I think of C arrays as syntactic sugar for initialized pointers.  Thus
>	char foo[] = "I am an anonymous char *";
>is an abbreviation for
>	register char *const foo = "I am an anonymous char *";

This is very wrong, but I'll let Chris Torek explain why, since he already has
it in his FAQ database.

Karl W. Z. Heuer (ima!haddock!karl or karl@haddock.isc.com), The Walking Lint