bph@buengc.BU.EDU (Blair P. Houghton) (05/10/89)
In article <FLEE.89May8171524@shire.cs.psu.edu> flee@shire.cs.psu.edu (Felix Lee) writes: >Here's an extraordinarily silly idea for <default.h>. Since the list > >Now, being able to say something like #pragma dumpdefines at an >arbitrary point would be interesting. Here's an extraordinarily neophytic question: What does a #pragma _do_, anyway? Tain't the C (nor CPP) I'm used to. --Blair "Back in the 20's, when I had to walk to school four--no, FIVE-- miles in the snow, and the only keywords in C were 'if' and 'struct'..."
karl@haddock.ima.isc.com (Karl Heuer) (05/10/89)
(Followups to comp.std.c; this is not a unix question.)
This guy walks into a bar with 500 #pragma's. In article <2810@buengc.BU.EDU>
the bartender says,
>What does a #pragma _do_, anyway?
So the guy says, "Anything it wants!"
(With apologies to any 500# gorillas in the audience.)
Seriously, though, #pragma is the universal escape to allow implementors to
do the sorts of things that they just *have* to add to the language (e.g.
`#module' or `#ident'), in such a way that it won't interfere with other ANSI-
conforming implementations.
Karl W. Z. Heuer (ima!haddock!karl or karl@haddock.isc.com), The Walking Lint
(Oh, wow! I actually used `#' as a pound sign!)henry@utzoo.uucp (Henry Spencer) (05/10/89)
In article <2810@buengc.BU.EDU> bph@buengc.bu.edu (Blair P. Houghton) writes: > What does a #pragma _do_, anyway? Whatever the compiler feels like. Really. It's an explicitly implementation-dependent "instructions to the compiler" directive. -- Mars in 1980s: USSR, 2 tries, | Henry Spencer at U of Toronto Zoology 2 failures; USA, 0 tries. | uunet!attcan!utzoo!henry henry@zoo.toronto.edu
jbu@sfsup.UUCP (+Urban J.) (05/12/89)
In article <2810@buengc.BU.EDU> bph@buengc.bu.edu (Blair P. Houghton) writes: > What does a #pragma _do_, anyway? > I've only seen #pragma used the in following context: #pragma pack(n) This is used to create structs whose layout is compatible with other machines. On UNIX System V/386 Release 3.2 (The Merged UNIX/XENIX Product) the CSDS 4.1.5 uses this to make some structures compatible with 80286 chip layout. So that AT&T PC 6300+ UNIX Programs and XENIX 286 programs can all read the same structures in the correct order (as the 80386 creates/writes/reads 'em). Sincerely, John Ben Urban
dmk@pilot.njin.net (David Katinsky) (05/12/89)
In my [brief] experience with pragmas, they were used to tweak the compiler
behavior.
dmk
--
David M. Katinsky
dmk@pilot.njin.net {wherever}!rutgers!dmk