逻辑非运算符在提升::精神::QI 中不起作用

the logical not operator not working in boost::spirit::qi

本文关键字:精神 QI 不起作用 运算符      更新时间:2023-10-16

如果在 qi::grammar 中,我使用此基本规则

expression = (boost::spirit::ascii::string("aaa"));

它将解析"AAA",仅此而已

当我使用这个(注意!)时,它根本不解析任何内容,而我希望它在除"aaa"之外的所有内容上都成功

expression = !(boost::spirit::ascii::string("aaa"));

我会错过一些包含吗?我正在使用提升 1.54.0。

编辑:

抱歉,这有点草稿,我为我的第一次试验修改了计算器示例......

#include <boost/config/warning_disable.hpp>
#include <boost/spirit/include/qi.hpp>
#include <boost/spirit/include/phoenix_operator.hpp>
#include <iostream>
#include <string>
#include <boost/spirit/include/qi_lit.hpp>
#include <boost/spirit/include/qi_not_predicate.hpp>
/*
 * 
    __grammar_calculator.cpp
HEADERS += 
    __grammar_calculator.h
 */
namespace client
{
    namespace qi = boost::spirit::qi;
    namespace ascii = boost::spirit::ascii;
    ///////////////////////////////////////////////////////////////////////////
    //  Our calculator grammar
    ///////////////////////////////////////////////////////////////////////////
    template <typename Iterator>
    struct calculator : qi::grammar<Iterator, int(), ascii::space_type>
    {
        calculator() : calculator::base_type(expression)
        {
            using qi::_val;
            using qi::_1;
            using qi::uint_;
            using boost::spirit::qi::lit;
            using boost::spirit::ascii::string;
            expression = !(boost::spirit::ascii::string("aaa"));
        }
        qi::rule<Iterator, int(), ascii::space_type> expression, term, factor;
    };
}
///////////////////////////////////////////////////////////////////////////////
//  Main program
///////////////////////////////////////////////////////////////////////////////
int
main()
{
    std::cout << "/////////////////////////////////////////////////////////nn";
    std::cout << "Expression parser...nn";
    std::cout << "/////////////////////////////////////////////////////////nn";
    std::cout << "Type an expression...or [q or Q] to quitnn";
    using boost::spirit::ascii::space;
    typedef std::string::const_iterator iterator_type;
    typedef client::calculator<iterator_type> calculator;
    calculator calc; // Our grammar
    std::string str;
    int result;
    while (std::getline(std::cin, str))
    {
        if (str.empty() || str[0] == 'q' || str[0] == 'Q')
            break;
        std::string::const_iterator iter = str.begin();
        std::string::const_iterator end = str.end();
        bool r = phrase_parse(iter, end, calc, space, result);
        if (r && iter == end)
        {
            std::cout << "-------------------------n";
            std::cout << "Parsing succeededn";
            //std::cout << "result = " << result << std::endl;
            std::cout << "-------------------------n";
        }
        else
        {
            std::string rest(iter, end);
            std::cout << "-------------------------n";
            std::cout << "Parsing failedn";
            //std::cout << "stopped at: ": " << rest << ""n";
            std::cout << "-------------------------n";
        }
    }
    std::cout << "Bye... :-) nn";
    return 0;
}

编辑2:

同样的一个更干净一点:

#include <boost/config/warning_disable.hpp>
#include <boost/spirit/include/qi.hpp>
#include <iostream>
#include <string>
#include <boost/spirit/include/qi_not_predicate.hpp>
namespace client
{
    namespace qi = boost::spirit::qi;
    namespace ascii = boost::spirit::ascii;
    template <typename Iterator>
    struct test : qi::grammar<Iterator>
    {
        test() : test::base_type(expression)
        {
            using boost::spirit::ascii::string;
            expression = (boost::spirit::ascii::string("aaa"));
        }
        qi::rule<Iterator> expression;
    };
}
int main()
{
    std::cout << "/////////////////////////////////////////////////////////nn";
    std::cout << "Expression parser...nn";
    std::cout << "/////////////////////////////////////////////////////////nn";
    std::cout << "Type an expression...or [q or Q] to quitnn";
    using boost::spirit::ascii::space;
    typedef std::string::const_iterator iterator_type;
    typedef client::test<iterator_type> test;
    test tester; // Our grammar
    std::string str;
    while (std::getline(std::cin, str))
    {
        if (str.empty() || str[0] == 'q' || str[0] == 'Q')
            break;
        std::string::const_iterator iter = str.begin();
        std::string::const_iterator end = str.end();
        bool r = phrase_parse(iter, end, tester, space);
        if (r && iter == end)
        {
            std::cout << "-------------------------n";
            std::cout << "Parsing succeededn";
            std::cout << "-------------------------n";
        }
        else
        {
            std::string rest(iter, end);
            std::cout << "-------------------------n";
            std::cout << "Parsing failedn";
            std::cout << "-------------------------n";
        }
    }
    std::cout << "Bye... :-) nn";
    return 0;
}

答:

问题来自测试:

if (r && iter == end)

正如所指出的,运算符没有消耗任何东西,所以 iter!=end

在下文中,Sehe提供了一些替代方案。

对于它的价值:

  • 正如其他人指出的那样,operator&operator!零宽度的前瞻断言(它们不匹配而是"窥视",匹配成功或失败)。

你会想知道

  • 否定字符集:

    qi::char_("a-z")    // matches lowercase letters
    

    ~qi::char_("a-z")//匹配除小写字母以外的任何内容

  • "解析器减法" - 考虑异常:

    qi::char_ - qi::char_("a-z")  // equivalent to ~qi::char_("a-z") 
    qi::char_("a-z") - "keyword"  // any lowercase letters, but not if it spells "keyword" 
    

编辑以便向前扫描到下一个"%{",您可以执行以下操作

qi::omit [ qi::char_ - "{%" ] >> "{%"

请注意,您并不总是需要将文本"包装"在qi::lit中,除非表达式尚未涉及 Qi 域中的原始表达式。


编辑 2 如何使用!&的示例:

&qi::int_ >> +qi::char_   // parse a string, **iff** it starts with an integer

!keyword_list >> identifier // parse any identifier that's not a known keyword