boost::spirit block of C++ code
I created this parser and it is working for me except the detail: //------------------ //the body of the block cpp_code_block_text = *(anychar_p-ch_p('{')-ch_p('}')); //the code begins with '{' cpp_code_block_begin_p = ch_p('{'); //the code ends with '}' cpp_code_block_end_p = ch_p('}'); //parser: cpp_code_block_p = cpp_code_block_begin_p >> repeat_p (0, 100)[(cpp_code_block_p|cpp_code_block_text)] >> cpp_code_block_end_p; ---------------------- Here is the text I'm using for tests: {asas {bbbbbb bbb b b { asa}bb bbb b bb } as {aaaa} {aaaacc} asasa {} aaa } 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? Thank you very much for reply.
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
Hi João!
I have adjusted the code according to your advise and the FAQ and it
is now working for me.
Here is the update:
//----------------
cpp_code_block_text = anychar_p-(ch_p('{')|ch_p('}'));
cpp_code_block_begin_p = ch_p('{');
cpp_code_block_end_p = ch_p('}');
cpp_code_block_p =
cpp_code_block_begin_p
>>
*(cpp_code_block_p|cpp_code_block_text)
>>
cpp_code_block_end_p;
At the first sight the boost::spirit seems to be difficult to use but
with more experience I recognize that it is realy nice/good tool.
Thank you João.
On 17/01/06, João Abecasis
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
_______________________________________________ Boost-users mailing list Boost-users@lists.boost.org http://lists.boost.org/mailman/listinfo.cgi/boost-users
participants (2)
-
elviin -
João Abecasis