Re: [boost] [test] como doesn't like #warning

From: Paul Mensonides (pmenso57_at_[hidden])
Date: 2005-12-20 04:47:02

> -----Original Message-----
> From: boost-bounces_at_[hidden] 
> [mailto:boost-bounces_at_[hidden]] On Behalf Of Paul Mensonides

> > So if I understand you correctly, it should just skip over any 
> > gibberish it might encounter until the matching #endif is found?
> 
> Yes, except that it still must tokenize the block.  You can 
> still get errors in tokenization, such as:
> 
> #if 0
>  "half-open // error
> #endif
> 
> > Is the preprocessor allowed to issue warnings about the gibberish?
> 
> The main point about the above is that the block must be 
> tokenized, but it should not be parsed to produce directives 
> or scanned for macro replacement.

What I said here isn't quite correct, so I'll elaborate.  The block has to be
parsed just enough to determine nested conditional compilation blocks.  E.g.

#if 0
   #if 0
   #endif
#endif

...but it isn't supposed to parse anything else--including an operands to
directives.  So, the following should still work:

#if 0
   #if // no expression!
   #endif
#endif

So, basically, the only parse is to tell if a name following '#' on a new line
is one of the conditional compilation directives or not.  Specifically, from
16.1/6, "...the group that it controls is skipped: directives are processed only
through the name that determines the directive in order to keep track of the
level of nested conditionals; the rest of the directives' preprocessing tokens
are ignored, as are the other preprocessing tokens in the group."

Regards,
Paul Mensonides