Boost C++ Libraries: Ticket #10193: [Spirit.qi] real_parser is too strict with the exponent part

component changed; owner set

viboes — Wed, 23 Jul 2014 21:08:19 GMT

owner set to Joel de Guzman
component None → spirit

status changed; resolution set

Joel de Guzman — Thu, 24 Jul 2014 01:03:37 GMT

status new → closed
resolution → invalid

No, that is incorrect. '4e' is a valid real number even without an integer following it. The grammar in the docs is correct. No exceptions are thrown. It parses '4e' just fine. If that's not you want, then you can customize the real number parser.

See http://en.cppreference.com/w/cpp/language/floating_literal

If you do not agree with this, please start a discussion in the Spirit mailing list. I'm closing this one as invalid.

olegmax@… — Mon, 11 Aug 2014 07:05:47 GMT

Replying to djowel:

The grammar in the docs is correct. It parses '4e' just fine.

No, it is not. exponent_part grammar in docs requires at least one digit after 'e'. How can it match '4e'?

status changed; resolution deleted

olegmax@… — Mon, 11 Aug 2014 07:07:08 GMT

status closed → reopened
resolution invalid

Joel de Guzman — Mon, 11 Aug 2014 08:46:22 GMT

Sorry, you are right. OK, let me try again...

Joel de Guzman — Mon, 11 Aug 2014 09:10:21 GMT

OK, second try. Pardon the confusion. 42e is indeed not valid. What was I thinking!

OK, here's what's happening. The parser parses 4e and attempts to find a number after that. So, 4em is not a double number and it fails. If I understand correctly, what you want is this:

exponent_part = -((lit('e') | 'E') >> -sign >> +digit);

Is that correct? In other words, the whole exponent part is optional. I think that makes sense. I reopened this as a bug.

olegmax@… — Mon, 11 Aug 2014 09:40:50 GMT

Replying to djowel:

If I understand correctly, what you want is this:

exponent_part = -((lit('e') | 'E') >> -sign >> +digit);

Grammar in documentation is already treats exponent_part as optional. So, preferred solution for me as a library user is to sync code with existing grammar description. Not sure whether you may break backward compatibility in this case. May be additional option should be added...

Btw, grammar in documentation doesn't permit dot before exponent part (integer only mantissa), but I'm almost sure that actual code permits it.

status changed; resolution set

Joel de Guzman — Mon, 11 Aug 2014 09:55:39 GMT

status reopened → closed
resolution → fixed

Joel de Guzman — Mon, 11 Aug 2014 09:57:46 GMT

It's fixed now in devel branch. Thanks for your diligence and sorry for my confusion.