Re: [Boost-users] help with boost::spirit:parsing out a list of menuitems

Subject: Re: [Boost-users] help with boost::spirit:parsing out a list of menuitems
From: Littlefield, Tyler (tyler_at_[hidden])
Date: 2011-10-13 11:52:50

Hello:
Thanks for the info. I've put in a couple questions below:
On 10/13/2011 2:42 AM, TONGARI wrote:
> 2011/10/13 Littlefield, Tyler <tyler_at_[hidden] 
> <mailto:tyler_at_[hidden]>>
>
>     Hello:
>     I have a client I'm writing, where the server sends data to the
>     client to display as a menu in one instance. I wanted to use
>     boost::spirit to parse this out. So, here's the code.
>     I have three questions:
>     1) What can I do better/differently?
>     2) When I parse out my menuitem, if there's no flag, can it be set
>     to 0 by default somehow?
>
>
> See: http://boost-spirit.com/home/articles/doc-addendum/faq/#default
awesome, thanks.

>     3) Where is menuitem returned?
>
>
> The synthesized attribute you pass in (if any).

> I'm confused here. Would someone mind explaining? I pass in menuitem() 
> to one of the templates, but I'm not sure what that returns.

>     Is there a way I can push it to a queue since I'll have more?
>
>
> By either auto attribute propagation or semantic action.
> I suggest the former if possible.
>
I'm not sure how to use the first. The second seems sort of easy, I 
would just use a function to do that, no? so:
pstart >> item[boost::bind(&Parser::PushMenuItem, this, _1)] >> *(delem 
 >> item[boost::bind(&Parser::PushMenuItem, this, _1)] >> pend;
?

>     My actual parser will look something like:
>     pstart >> item >> *(delem >> item) >> pend;
>
>
> FYI,  "item >> *(delem >> item)" can be replaced with "item % delem".
>
so the former would just be: pstart >> item[...]%delem >> pend;
?

>     Here is the code I have currently:
>     struct menuitem
>     {
>     std::string name;
>     int flag;
>     int choice;
>     };
>
>     BOOST_FUSION_ADAPT_STRUCT(
>                              menuitem,
>                              (std::string, name)
>                              (int, flag)
>                              (int, choice))
>
>                              namespace ascii = boost::spirit::ascii;
>     namespace qi = boost::spirit::qi;
>
>     //I'd like to just take a char* here, since that's my payload.
>     copying the char* to a std::string will take extra time, is there
>     a way to do that?
>
>
>
> const std::string &data -> char const* data
> std::string::const_ iterator -> char const*
> data.begin() -> data
> data.end() -> data + length
>
> ...and so on
>
awesome, thanks. I didn't know that I could use that rather than an iterator

>     BOOL Menu::Parse(const std::string &data, int length)
>     {
>        std::string::const_iterator it, itEnd;
>        it = data.begin();
>        itEnd = data.end();
>
>        //we construct a few parsers to make things easier.
>
>        qi::rule<std::string::const_ iterator, char, ascii::space_type>
>     pstart = qi::char_('[');
>        qi::rule<std::string::const_ iterator, char, ascii::space_type>
>     pend = qi::char_(']');
>        qi::rule<std::string::const_ iterator, char,
>     ascii::space_type>delem = qi::char_('|');
>        qi::rule<std::string::const_ iterator, menuitem(),
>     ascii::space_type>item = qi::char_("a-zA-Z0-9 -.?!$@") >>
>     qi::char_('(') >> -qi::int_ >> qi::char_(':') >> qi::int_ >>
>     qi::char_(')');
>
>        if (!qi::phrase_parse(it, itEnd, pstart >> item >> pend,
>     ascii::space))
>        {
>            return false;
>        }
>        return true;
>     }
>
>
>
>
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-- 
Take care,
Ty
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