Path: utzoo!attcan!uunet!lll-winken!lll-tis!helios.ee.lbl.gov!pasteur!ucbvax!VENUS.YCC.YALE.EDU!LEICHTER
From: LEICHTER@VENUS.YCC.YALE.EDU ("Jerry Leichter ", LEICHTER-JERRY@CS.YALE.EDU)
Newsgroups: comp.os.vms
Subject: Re: flex (really, re "noshare")
Message-ID: <8805260107.AA12954@ucbvax.Berkeley.EDU>
Date: 24 May 88 03:15:00 GMT
Sender: daemon@ucbvax.BERKELEY.EDU
Organization: The Internet
Lines: 38


	:> The 'C' question: :>   Flex has the following global line:
	:>      FILE *yyin=stdin, *yyout=stdout;
	:>   which does not work at compile time on VMS.  In other words, it
	:>   appears the compiler does not treat stdin as a constant--it's
	:>   value is known only at run-time.  (VMS stdio.h says
	:>   "extern noshare FILE *stdin;.) To work 
	:
	:According to the latest ANSI draft (and many of the previous ones),
	:stdin and friends are simply expressions and not necessarily
	:constant expressions.  Thus, they may not be used portably to
	:initialize objects with static storage duration.  So, the compiler's
	:OK, flex is not maximally portable (as you

	If the compiler's OK, what's this "noshare" business?  It's been  a
	while since I've seen the ANSI C draft, but I don't remember that
	being in it - it looks kind of like noalias?  (Noalias had to go, and
	did - it was non-negotiable.)  Also, something you declare to be
	extern shouldn't be assumed to be constant.  So both are somewhat
	non-portable.

"noshare" is a VAX C extension to control storage allocation; it is mainly
needed when creating shared images --- it says that the variable is to go
into a "copy on reference" segment, rather than being shared among all users
of the shared image.  Since the VAX C run-time library, including all the code
for such things as printf, normally lives in a shared library (VAXCRTL.EXE),
you can see that stdio had better be "noshare" unless you want everyone on
the system writing to the same standard output!

"noshare" pre-dates ANSI, which it is certainly not compatible with.  It could
presumably be replaced with a #pragma or something like "__noshare" to be
compatible.

Whether it can appear in the declaration of stdin and friends is an interes-
ting question.  What it comes down to is:  Does the ANSI spec guarantee a
particular declaration syntax for these things, or does it simply guarantee
that some sort of appropriate - but system-specific - definition will be
available if stdio.h is included.
							-- Jerry