System V preprocessor problem with <generic.h>

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2 total messages Started by Jonathan P. Leech Fri, 25 Apr 1986 04:56

#169

Author: Jonathan P. Leech
Date: Fri, 25 Apr 1986 04:56

39 lines
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Organization : California Institute of Technology
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    The <generic.h> header file defines constructs of the form

	#define name2(a,b) a\
	b
	#define name3(a,b,c) a\
	b\
	c

    with the intent of producing

	name2(a,b) => ab    etc.

    unfortunately the  System  V  cpp  (at  least  the	HP  and  ELXSI
versions) instead produces

	name2(a,b) => a b

    this is a serious problem in  every  case  I  can  find  of  these
constructs  being  used  -  specifically  <vector.h>.  I  don't  think
there's any way to produce this behavior with the System V cpp.

    Combined with the problem of '//' comments	not  being  elided  by
cpp, I think C++ should come with its own  preprocessor  (or  have  it
integrated into cfront).

    Additional	amusement:  try  running  cpp  with  input  from  your
keyboard and #include <generic.h>. Note that it now takes > 1  EOF  to
get out of cpp!
-- 
    Jon Leech (jon@csvax.caltech.edu || ...seismo!cit-vax!jon)
    Caltech Computer Science Graphics Group
    __@/

Re: System V preprocessor problem with <generic.h>

#162

Author: guy
Date: Tue, 29 Apr 1986 02:11

22 lines
1311 bytes

> Try this fix for system V cpp:
> 
> 	#define name2(a,b)	a/**/b
> 	#define name3(a,b,c)	a/**/b/**/c
> 
> This works because the system V cpp strips the comments from the input.

So do earlier versions of Reiser's "cpp"; this is the "canonical" way of
concatenating two arguments to a macro, and is heavily used in 4BSD.  It
has, however, two problems:

	1) If you run your code through "lint", it won't work - "cpp"
	   is run by "lint" with the "-C" flag, which tells it not to
	   strip comments (for obvious reasons).

	2) It is not a guaranteed property of the C language, but a
	   quirk of the implementation, so it will not work in
	   general.
-- 
	Guy Harris
	{ihnp4, decvax, seismo, decwrl, ...}!sun!guy
	guy@sun.arpa

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