umsmigie@ccu.umanitoba.ca (Jason Smigiel) (02/10/91)
Is it common practice not to structure preprocessor commands in ANSI C?
I've been staring at code that reads like this:
#if defined(MSDOS)
#if defined(ANSI)
#include "ms_ansi.h"
#endif
#else /* not msdos */
#if !defined(ATARIST_MWC) && !defined(MAC) && !defined(AMIGA)
#ifndef VMS
#include <sys/ioctl.h>
#endif
#include <signal.h>
#endif
#endif
While it makes a lot more sense to me to write it something like this:
#if defined(MSDOS)
#if defined(ANSI)
#include "ms_ansi.h"
#endif
#else /* not msdos */
#if !defined(ATARIST_MWC) && !defined(MAC) && !defined(AMIGA)
#ifndef VMS
#include <sys/ioctl.h>
#endif
#include <signal.h>
#endif
#endif
I looked in the K&R2 reference manual, under A12,(very first paragraph) and
it states:
"Lines beginning with #, perhaps preceeded by white space, communicate
with this preprocessor."
So it seems completely valid to me, I just wanted to know if this was a smart
thing to do or am I entirely insane?
Jason Smigiel
umsmigie@ccu.umanitoba.cascs@adam.mit.edu (Steve Summit) (02/11/91)
In article <1991Feb10.063915.5476@ccu.umanitoba.ca>, Jason Smigiel writes: >Is it common practice not to structure preprocessor commands in ANSI C? >I looked in the K&R2 reference manual, under A12,(very first paragraph) and >it states: > > "Lines beginning with #, perhaps preceded by white space, communicate > with this preprocessor." > > So it seems completely valid to me, I just wanted to know if this was a >smart thing to do or am I entirely insane? You're not insane. However, leading whitespace before preprocessor directives is a relatively new "innovation." Older compilers do not allow it, and there are enough of them around that people tend not to use leading whitespace at all. Furthermore, those of us who have been using the older compilers for years are so used to it that nicely indented nested #if's look, well, pretty weird. You're correct, though, in thinking that more nicely structured #if's would be better. What I can't explain is why the following style, which most old compilers would accept, has never been widespread (and which therefore looks equally weird to me): #if defined(MSDOS) # if defined(ANSI) # include "ms_ansi.h" # endif #else /* not msdos */ # if !defined(ATARIST_MWC) && !defined(MAC) && !defined(AMIGA) # ifndef VMS # include <sys/ioctl.h> # endif # include <signal.h> # endif #endif For all the ranting that I and others do about the importance of good style and clear program layout, there are always these little hypocrisies. Steve Summit scs@adam.mit.edu
datangua@watmath.waterloo.edu (David Tanguay) (02/11/91)
In article <1991Feb10.204604.28908@athena.mit.edu> scs@adam.mit.edu writes: |For all the ranting that I and others do about the importance of |good style and clear program layout, there are always these |little hypocrisies. | Steve Summit Corollory: All the logical, rational, and pragmatic arguments in the world will not convince my *eyes* that your code layout is better than mine. :-) -- David Tanguay Software Development Group, University of Waterloo
barmar@think.com (Barry Margolin) (02/11/91)
In article <1991Feb10.204604.28908@athena.mit.edu> scs@adam.mit.edu writes: >What I can't explain is why the following style, which most old >compilers would accept, has never been widespread > #if defined(MSDOS) > # if defined(ANSI) I think it's because most people think of the "#" and the keyword as one token ("#if"), even though the language officially considers them independent (the "#" preprocessor indicator followed by the "if" pp command). -- Barry Margolin, Thinking Machines Corp. barmar@think.com {uunet,harvard}!think!barmar
gwyn@smoke.brl.mil (Doug Gwyn) (02/11/91)
In article <1991Feb10.063915.5476@ccu.umanitoba.ca> umsmigie@ccu.umanitoba.ca (Jason Smigiel) writes: >Is it common practice not to structure preprocessor commands in ANSI C? You mean, not to indent them. The answer is, yes. >So it seems completely valid to me, I just wanted to know if this was a smart >thing to do or am I entirely insane? Many existing (pre-ANSI) C preprocessors are not tolerant of white space before the #.
dgil@pa.reuter.COM (Dave Gillett) (02/12/91)
In <1991Feb10.063915.5476@ccu.umanitoba.ca> umsmigie@ccu.umanitoba.ca (Jason Smigiel) writes: >Is it common practice not to structure preprocessor commands in ANSI C? ^^^^^^^^^ The word "structure", as a noun and a verb, has a variety of meanings that are useful in a programming context. However, its use as a verb synonymous (according to Jason's example) with "indent" is not among those. Indentation is commonly used as a technique to make structure visible, but it is not structure in a programming sense and should never be mistaken for it. Dave
daw@cbnewsh.att.com (David Wolverton) (02/14/91)
In article <1991Feb10.204604.28908@athena.mit.edu>, scs@adam.mit.edu (Steve Summit) writes: > What I can't explain is why the following style, which most old > compilers would accept, has never been widespread (and which > therefore looks equally weird to me): > > #if defined(MSDOS) > # if defined(ANSI) > # include "ms_ansi.h" > # endif > #else /* not msdos */ > # if !defined(ATARIST_MWC) && !defined(MAC) && !defined(AMIGA) > # ifndef VMS > # include <sys/ioctl.h> > # endif > # include <signal.h> > # endif > #endif I experimented with this style, but never really fully adopted it, partly because it isn't widespread, as Steve points out. But another reason was the early lack of "#elif", which makes the indentation sometimes look a little weird: #if CHOICE_1 # define FOO "abcd" #else /* would rather have a single */ #if CHOICE_2 /* #elif CHOICE_2 here */ # define FOO "efgh" #else #if CHOICE_3 # define FOO "ijkl" #endif /* trebled #endif's due to lack */ #endif /* of #elif */ #endif Unfortunately, it often seemed to me that precisely the times when using indentation would clarify the meaning were also the times when #elif was useful. Dave Wolverton daw@attunix.att.com