Article View: comp.std.c
Article #2690Re: #if query
From: Chris Torek
Date: Sat, 06 Apr 1991 00:35
Date: Sat, 06 Apr 1991 00:35
35 lines
1311 bytes
1311 bytes
In article <1991Apr5.161945.889@vixvax.mgi.com> cepek@vixvax.mgi.com writes: >Does ANSI really state that > > #if ABC == DEF > >evaluates to FALSE if symbol DEF is not defined!? No. However, in this case, #if DEF is the same as #if 0 Furthermore, if ABC is either #define'd as the preprocessor value 0 (i.e., a preprocessor expression which evaluates to 0) or is undefined, #if ABC == DEF is the same as #if 0 == 0 or #if 1 X3.159-1989 merely states that at that particular point in preprocessor arithmetic, all `variable names' are treated as zero. (Macro expansion has already taken place, replacing any #define'd tokens with their definitions.) -- In-Real-Life: Chris Torek, Lawrence Berkeley Lab CSE/EE (+1 415 486 5427) Berkeley, CA Domain: torek@ee.lbl.gov
Technical Details
Message-ID:
<11854@dog.ee.lbl.gov>Path:
arc1-ca.pugleaf.net!utzoo!utgpu!news-server.csri.toronto.edu!rpi!zaphod.mps.ohio-state.edu!swrinde!ucsd!dog.ee.lbl.gov!elf.ee.lbl.gov!torekReferences:
<1991Apr5.161945.889@vixvax.mgi.com>Show Full Headers
Complete Article Headers
Path: arc1-ca.pugleaf.net!utzoo!utgpu!news-server.csri.toronto.edu!rpi!zaphod.mps.ohio-state.edu!swrinde!ucsd!dog.ee.lbl.gov!elf.ee.lbl.gov!torek From: torek@elf.ee.lbl.gov (Chris Torek) Newsgroups: comp.std.c Subject: Re: #if query Message-ID: <11854@dog.ee.lbl.gov> Date: 6 Apr 91 00:35:08 GMT References: <1991Apr5.161945.889@vixvax.mgi.com> Reply-To: torek@elf.ee.lbl.gov (Chris Torek) Organization: Lawrence Berkeley Laboratory, Berkeley Lines: 35 X-Local-Date: Fri, 5 Apr 91 16:35:09 PST