[Spirit]Kleene star with arguments having optional attributes.

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Paul Graphov

24 Nov 2010 24 Nov '10

10:06 a.m.

Hello Boost Users, I'm now building configuration file parser with Boost.Spirit. I have a little trouble understanding how this parser builds attribute: It was supposed to parse strings throwing 'p' letter away. *((qi::char_ - 'p') | qi::lit('p')) attribute of qi::lit is Unused. attribute of (qi::char_ - 'p') is char. so attribute of ((qi::char_ - 'p') | qi::lit('p')) should be optional<char> that is uninitialized optional value when matched against character 'p' After applying Kleene star it should became vector. It seems to be compatible with string (at least it compiles). But 'p' letters are not thrown away. The full example is here: http://pastebin.com/tCMw22Zy The output of that example is: Full parsing Result: "abcpppdef" Is it possible to make such a parser without using semantic actions like [bind(&string::append, res, _1)] or something like that, which seem to be less elegant solution. Thanks!

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Paul Graphov

24 Nov 24 Nov

10:26 a.m.

New subject: [Spirit]Kleene star with arguments having optional attributes.

I've suddenly found a solution like this: *((qi::char_ - 'p') >> qi::omit[*qi::lit('p')]) But nevertheless it is interesting for me why my first attempt was wrong and how should I understand its behavior. Thanks. On 24 November 2010 13:06, Paul Graphov wrote:

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Hello Boost Users,

I'm now building configuration file parser with Boost.Spirit. I have a little trouble understanding how this parser builds attribute:

It was supposed to parse strings throwing 'p' letter away.

*((qi::char_ - 'p') | qi::lit('p'))

attribute of qi::lit is Unused. attribute of (qi::char_ - 'p') is char.

so attribute of ((qi::char_ - 'p') | qi::lit('p')) should be optional<char> that is uninitialized optional value when matched against character 'p'

After applying Kleene star it should became vector. It seems to be compatible with string (at least it compiles). But 'p' letters are not thrown away.

The full example is here: http://pastebin.com/tCMw22Zy

The output of that example is: Full parsing Result: "abcpppdef"

Is it possible to make such a parser without using semantic actions like [bind(&string::append, res, _1)] or something like that, which seem to be less elegant solution.

Thanks!

TONGARI

12:49 p.m.

New subject: [Spirit]Kleene star with arguments having optional attributes.

2010/11/24, Paul Graphov :

...

Is it possible to make such a parser without using semantic actions like [bind(&string::append, res, _1)] or something like that, which seem to be less elegant solution.

The following works as expected: std::vector vec; bool r = qi::parse(begin, end, *('p' | qi::char_), vec); Why std::string does not? I have no idea, either. You can go to https://lists.sourceforge.net/lists/listinfo/spirit-general for more specific help.

Paul Graphov

1:50 p.m.

New subject: [Spirit]Kleene star with arguments having optional attributes.

Thanks, I didn't know that there is a dedicated Spirit mailing list. On 24 November 2010 15:49, TONGARI wrote:

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2010/11/24, Paul Graphov :

...
Is it possible to make such a parser without using semantic actions like [bind(&string::append, res, _1)] or something like that, which seem to be less elegant solution.

The following works as expected:

std::vector vec; bool r = qi::parse(begin, end, *('p' | qi::char_), vec);

Why std::string does not? I have no idea, either.

You can go to https://lists.sourceforge.net/lists/listinfo/spirit-general for more specific help. _______________________________________________ Boost-users mailing list Boost-users@lists.boost.org http://lists.boost.org/mailman/listinfo.cgi/boost-users

TONGARI

1:57 p.m.

New subject: [Spirit]Kleene star with arguments having optional attributes.

BTW, you can use qi::skip in this case: bool r = qi::parse(begin, end, qi::skip('p')[*qi::char_], res); it seems well-suited here. 2010/11/24, Paul Graphov :

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Thanks, I didn't know that there is a dedicated Spirit mailing list.

On 24 November 2010 15:49, TONGARI wrote:

...
2010/11/24, Paul Graphov :

...
Is it possible to make such a parser without using semantic actions like [bind(&string::append, res, _1)] or something like that, which seem to be less elegant solution.

The following works as expected:

std::vector vec; bool r = qi::parse(begin, end, *('p' | qi::char_), vec);

Why std::string does not? I have no idea, either.

You can go to https://lists.sourceforge.net/lists/listinfo/spirit-general for more specific help. _______________________________________________ Boost-users mailing list Boost-users@lists.boost.org http://lists.boost.org/mailman/listinfo.cgi/boost-users

Torri, Stephen CIV NSWCDD, W15

1:59 p.m.

New subject: [Spirit]Kleene star with arguments havingoptional attributes.

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From: boost-users-bounces@lists.boost.org on behalf of TONGARI Sent: Wed 11/24/2010 7:49 AM To: boost-users@lists.boost.org Subject: Re: [Boost-users] [Spirit]Kleene star with arguments havingoptional attributes.

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2010/11/24, Paul Graphov : Is it possible to make such a parser without using semantic actions like [bind(&string::append, res, _1)] or something like that, which seem to be less elegant solution.

The following works as expected:

std::vector vec; bool r = qi::parse(begin, end, *('p' | qi::char_), vec);

Why std::string does not? I have no idea, either.

If you can in the future providing a stand alone example describing a problem is very helpful in giving you a good answer. What I see from the simple grammar is that you are looking for a sequence of characters. The 'qi::char_' will parse any single character (see http://www.boost.org/doc/libs/1_45_0/libs/spirit/doc/html/spirit/qi/referenc...). The 'p' is a qi literal which is not meant to be parsed into the output string. I found in a simple example I used below that the 'p' character was placed in the output. I think the | operator used the qi::char_ to parse the 'p' character. Here is my example which places the parsed input string into a std::string. What is happening beneath the code is that the sequence of zero or more characters is that is being placed into a std::vector<char> which happens to be automatically promoted into a std::string. Since I did not have the original email does this solve your problem? Stephen ------------------- #include #include <iostream> int main (int, char**) { std::string input = "apapa"; std::string::const_iterator begin = input.begin(); std::string::const_iterator end = input.end(); std::string output; bool r = boost::spirit::qi::parse ( begin, end, *(boost::spirit::qi::lit('p')|boost::spirit::qi::char_), output ); if ( r ) { std::cout << "Success: found - " << output << std::endl; } else { std::cout << "Failed to parse string" << std::endl; } return 0; }

Paul Graphov

25 Nov 25 Nov

8:32 a.m.

New subject: [Spirit]Kleene star with arguments havingoptional attributes.

Thanks for the answers. Stephen, you can look at original emails here: http://thread.gmane.org/gmane.comp.lib.boost.user/63995 The problem is solved although I don't yet understand that strange conversion from vector to string. Maybe I'll ask Spirit mailing list. qi::skip seems to be the best solution, thanks!

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Paul Graphov
TONGARI
Torri, Stephen CIV NSWCDD, W15