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: TONGARI (tongari95_at_[hidden])
Date: 2011-10-13 04:42:29

2011/10/13 Littlefield, Tyler <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

> 3) Where is menuitem returned?

The synthesized attribute you pass in (if any).

> 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.

My actual parser will look something like:
> pstart >> item >> *(delem >> item) >> pend;
>

FYI,  "item >> *(delem >> item)" can be replaced with "item % delem".

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

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;
> }
>