Re: [Boost-users] boost::spirit block of C++ code

From: João Abecasis (jpabecasis_at_[hidden])
Date: 2006-01-16 21:45:05

Hi!

elviin wrote:
> I created this parser and it is working for me
> except the detail:

[snip code]

> And the problem is in repeat_p (0, 100). I'd like to use * instead but
> it does not work for me because the parser runs forever. 100 means the
> number of blocks  cpp_code_block_p or cpp_code_block_text.
> 
> Where is the problem?

The code sample you provided can be summarized as

     continuation = *(anychar_p - (begin|end));
     all = begin >> *continuation >> end;

Which, substituting continuation, is the same as:

     all = begin >> *(*(anychar_p - (begin|end))) >> end;

The problem here is the double kleene star. The outer kleene will 
continue matching, in an infinite loop, as long as the inner one returns 
matches -- even if they're zero matches. Btw, this is a FAQ and is 
addressed here http://tinyurl.com/art36.

When you substitute the outer * for repeat_p(0, 100) you only limit the 
loop. You still get 100 matches, even if they're all empty.

The solution is pretty simple, and it is to remove one of the 
*/repeat_p. For instance,

     continuation = *(anychar_p - (begin|end));
     all = begin >> continuation >> end;

Best regards,

João