Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!ncar!tank!ux1.cso.uiuc.edu!ux1.cso.uiuc.edu!uxe.cso.uiuc.edu!mcdonald
From: mcdonald@uxe.cso.uiuc.edu
Newsgroups: comp.lang.c
Subject: Re: A solution to the multiple inclusio
Message-ID: <225800235@uxe.cso.uiuc.edu>
Date: 29 Oct 89 17:08:00 GMT
References: <14240@well.UUCP>
Lines: 32
Nf-ID: #R:well.UUCP:14240:uxe.cso.uiuc.edu:225800235:000:1067
Nf-From: uxe.cso.uiuc.edu!mcdonald    Oct 29 11:08:00 1989


    
   > >   #include FRED_H
    
>    Please be alert for problems.  K&R requires the token after the
>    "#include" to be a filename enclosed in double quotes or angle
>    brackets, not an arbitrary symbol.

Quoted without permission from "The C Programming Language" by
Kernighan and Ritchie, Prentice Hall, copyright 1988 (page231):

Finally, a directive of the form
   # include token-sequence

not matching one of the previous formsis interpreted by expanding the
token sequence as for normal text; one of the two forms with
<...> or "..." must result, and it is then treated as described
previously"

So, if FRED_H expands to "fred.h" it is perfectly legal. If is stays
as-is, it is illegal.

Another question arises: earlier K&R say "The characters in the filename
must not include >  [if it started with <] or the newline and 
the effect in undefined if it 
contains any of ", ',\, or /*."

Shouldn't that be "implementation defined" rather than undefined -
the most common operating system in the world uses "\" as a file
path separator.

Doug McDonald