Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP
Path: utzoo!dciem!nrcaer!cognos!geovision!alastair
From: alastair@geovision.UUCP (Alastair Mayer)
Newsgroups: comp.lang.c
Subject: Re: Portability and /**/
Message-ID: <118@geovision.UUCP>
Date: Tue, 28-Jul-87 16:03:46 EDT
Article-I.D.: geovisio.118
Posted: Tue Jul 28 16:03:46 1987
Date-Received: Fri, 31-Jul-87 01:20:10 EDT
References: <949@oakhill.UUCP> <23575@sun.uucp> <4983@prls.UUCP>
Reply-To: alastair@geovision.UUCP (Alastair Mayer)
Organization: Geovision Corporation, Ottawa, Canada
Lines: 44
Summary: Sometimes useful, cpp does it, different syntax between SysV and BSD

In article <4983@prls.UUCP> gardner@prls.UUCP (Robert Gardner) writes:
>We recently received a large amount of code written for our
>Unix VAX in C.  It's device driver routines make extensive use
>of an interesting construct -- a rather large number of #defines
>are of the form:
>#define a(n) a/**/n
>so that, for instance, a(2) expands to a2. 
> [...]  In pursuing this (out of curiosity), I
>found that the Ultrix VAX c compiler compiles the program
>    main()
>    {
>       int n2=2;
>       printf("%d\n",n/*comment*/2);
>    }
>and prints out '2' when executed.  This suggests that the pre-processor
>simply removes comments, rather than replacing them with white space.
>My Lightspeed C compiler at home will not compile the above program.
>Any comments on portability?
>
>Robert Gardner

You are right, the C pre-processor does (normally) strip out the comments.
However, the exact semantics depend on the particular version (BSD or
SYSV) of 'cpp'.  There *are* uses for this -- you note one.  The C++
compiler (which also uses 'cpp') uses a similar mechanism to allow definition
of generic classes.  The file <generic.h> has code something like:

    #ifdef BSD  /* BSD way */
    #define name2(a,b) a\
    b
    #else       /* System V way */
    #define name2(a,b) a/**/b
    #endif

You might try the former method with your Lightspeed C (never having used
it, I dunno if it'll work either).

As to portability, if you *must* catenate tokens like this, then #define
a macro to do it such as the above.
-- 
 Alastair JW Mayer     BIX: al
                      UUCP: ...!utzoo!dciem!nrcaer!cognos!geovision!alastair

(Why do they call it a signature file if I can't actually *sign* anything?)