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Boost Spirit在空字符串输入时失败

boost-spirit c++11

Max · 技术社区 · 8 年前

我试图解析以下字符串并提取括号内的部分。

此字符串失败:

_FIND('Something', '')_
Should return
part1 = 'Something'
part2 = ''

此字符串传递:

_FIND('Something', '*')_
Returns
part1 = 'Something'
part2 = '*'

我假设问题在于“quoted\u字符串”

    find_parser() : find_parser::base_type(start)
    {
        using qi::lit;
        using qi::lexeme;
        using standard_wide::char_;

        /// simple quoted string.
        quoted_string %= lexeme['\'' >> +(char_ - '\'') >> '\''];

        start %=
            -(lit("$(")) // optional
            >> lit("_FIND")
            >> '('
            >> quoted_string
            >> -(',' >> quoted_string) // 2nd parameter optional
            >> ")_"
            >> -(lit(")")) // optional
            ;
    }

        quoted_string %= lexeme['\'' >> +(char_ - '\'') >> '\''];
        empty_quoted_string %= lexeme['\'' >> +(qi::space - '\'') >> '\''];

        start %=
            lit("_FIND")
            >> '('
            >> (quoted_string|empty_quoted_string)
            >> -(',' >> (quoted_string|empty_quoted_string)) // 2nd parameter optional
            >> ")_"
            ;

我知道这一定是件简单的事,但我不能把我的手指放在上面。

感谢您的任何意见、提示或提示。

1 回复 | 直到 8 年前

sehe 8 年前

  lexeme['\'' >> +(char_ - '\'') >> '\''];

+p 意味着 p 必须 match one-or-more times . 如果必须接受空字符串,请使用 Kleene-star operator, which allows zero-or-more matches

  lexeme['\'' >> *(char_ - '\'') >> '\''];

现场演示

此外,不正确,其中 "$(_FIND('')" 或 "_FIND('')" 将解析为“正确”

Live On Coliru

#include <boost/spirit/include/qi.hpp>
#include <boost/fusion/adapted/std_pair.hpp>

using Params = std::pair<std::string, std::string>;

namespace qi = boost::spirit::qi;

template <typename It> 
struct find_parser : qi::grammar<It, Params()> {
    find_parser() : find_parser::base_type(start)
    {
        using namespace qi;

        start = skip(space) [ "$(" >> find >> ")" | find ];

        find
            = '_' >> lit("FIND") >> lit('(')
            >> quoted_string >> -(',' >> quoted_string) // 2nd parameter optional
            >> ')' >> '_'
            ;

        quoted_string = "'" >> *~char_("'") >> "'";

        BOOST_SPIRIT_DEBUG_NODES((start)(find)(quoted_string))
    }

  private:
    qi::rule<It, Params()> start;

    // rules with skipper
    qi::rule<It, Params(), qi::space_type> find;

    // implicit lexemes
    qi::rule<It, std::string()> quoted_string;
};

int main() {
    using It = std::string::const_iterator;
    find_parser<It> const p;

    for (std::string const input : {
            "_FIND('Something', 'Something else')_",
            "_ FIND('Something', 'Something else') _",
            "$(_FIND('Something', 'Something else')_)",
            "$( _FIND( 'Something', 'Something else' )_ )",
            // second arg empty
            "_FIND('Something', '')_",
            "_ FIND('Something', '') _",
            "$(_FIND('Something', '')_)",
            "$( _FIND( 'Something', '' )_ )",
            // optional args omitted
            "_FIND('Something')_",
            "_ FIND('Something') _",
            "$(_FIND('Something')_)",
            "$( _FIND( 'Something' )_ )",
            })
    {
        std::cout << "-------- " << input << " ------------\n";

        It f = input.begin(), l = input.end();
        Params parsed;
        if (parse(f, l, p, parsed))
            std::cout << "Parsed: '" << parsed.first << "', '" << parsed.second << "'\n";
        else
            std::cout << "Parsing failed\n";

        if (f!=l)
            std::cout << "  -- Remaining unparsed: '" << std::string(f,l) << "'\n";
    }
}