RE: Inconsistent hierarchy

[David Korn <dkorn at pixelpower dot com>]

>-----Original Message-----
>From: Jerry Miller [mailto:gmiller@cs.sunysb.edu]
>Sent: 22 February 2001 03:31
 
 [Rather an old one, but better late than never]

>It turns out that the string '/|\' is valid under PL/I, but
>it escapes the second single-quote under C.  However,
>the compiler seems to have no business whatsoever
>parsing something whose #ifdef condition has not been
>met.  It appears that the respective hierarchies of the
>quote symbol and the #ifdef/#endif pair are reversed
>between these two versions, and according to my own
>perception, it is the PC version whose behavior seems
>more intuitive.

  Well, there would be a slight problem with that: if you stop parsing
the moment you hit a #if 0, how do you know when to start parsing again?
At the very least you'd have to watch out for the #endif; and of course
you've got to watch out for nested #if-#endif pairs, so that you don't
start parsing again too easily, and it gets complex very quickly.

  I believe the C language standard actually specifies that everything
in the source file must be valid C preprocessing tokens, even if it is
enclosed in a #if 0.  It isn't to do with 'hierarchies' (I assume you
mean something like operator precedence here), and if it doesn't happen
on a newer version of the compiler I assume that means that somebody got
annoyed and did something about it.

  I ran across this problem for myself quite a while ago, since I used
to like doing stuff like...

#if 0

    ... code ...

 aha this code isn't finished yet so I shall use if 0 to stop it compiling

#endif

and the preprocessor complained about my unterminated character constant,
having taken the ' in "isn't" for the opening apostrophe of a character
constant.

  This isn't really a solution to your problem, because there isn't one
except to watch out for and correct those apostrophes as you encounter
them; sorry.

      DaveK
-- 
we are not seats or eyeballs or end users or consumers.
we are human beings - and our reach exceeds your grasp.
                    deal with it.                      - cluetrain.org 


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