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From: dan@rna.UUCP (Dan Ts'o)
Newsgroups: comp.lang.c,comp.bugs.4bsd
Subject: C preprocessor: undefined control
Message-ID: <435@rna.UUCP>
Date: 19 Mar 89 02:38:25 GMT
Organization: Rockefeller University - Neurobiology
Lines: 34


	I'm sure this must have been covered before, but I haven't seen it
myself...

	I am writing a (large) C program that runs under both UNIX and
MSDOS. I am using the Microsoft 5.0 C compiler for MSDOS and 4.3BSD's CC
for VAX UNIX. There is a portion of code that only is relevant under MSDOS.
It is surrounded by #ifdef MSDOS -> #endif. Within that code, I use MSC's
#pragma loop_opt(off) to suppress the loop optimization of a (volatile)
device register.
	The 4.3BSD complains about the #pragma, even though it should be
excluded entirely since the #ifdef MSDOS is not satisfied:

#ifdef MSDOS
	... C code ...
#pragma loop_opt(off)
	while(...)
	...
#endif

	I naturally see how this could happen, although I do consider it a
bug (what does ANSI say about this sort of thing). Is there any way around
this ? (I know I could write the C code such that the #pragma isn't
necessary... that's not an answer).

	Please email responses. Thanks.

				Cheers,
				Dan Ts'o		212-570-7671
				Dept. Neurobiology	dan@rna.rockefeller.edu
				Rockefeller Univ.	...cmcl2!rna!dan
				1230 York Ave.		rna!dan@nyu.edu
				NY, NY 10021		tso@rockefeller.arpa
							tso@rockvax.bitnet