c++ - Boost::spirit 从非终端获取值(value)

Question

我有这个，在我的 boost::spirit 语法中；

paren = (qi::token(LEFT_PAREN) >> character >> qi::token(RIGHT_PAREN)) [ build_paren ]
          ;
character = qi::token(CHARACTER) [ build_character]
          ;

这些被定义为；

qi::rule<Iterator> paren;
qi::rule<Iterator, char> character;

函数build_paren，具有以下原型(prototype)(通过编译器转换错误找到)；

void build_paren(boost::fusion::vector2<boost::iterator_range<__gnu_cxx::__normal_iterator<char*, std::basic_string<char>>>, boost::iterator_range<__gnu_cxx::__normal_iterator<char*, std::basic_string<char>>>> v)

这里的vector，持有两个字符串，分别是"(\0"和")\0"，这是我所期望的，但是我如何得到char 字符匹配？

真的，我想要的 build_paran 函数原型(prototype)是；

void build_paren(std::string left_paren, char character, std::string right_paren)

或者，同样，但是 char 参数作为列表中的最后一个。

Answer 1

你不必那么努力:)

Spirit 具有自动属性传播。实际上，我想说这是它的主要卖点。所以你可以:

char parsed_char;
bool ok = qi::phrase_parse(f,l, '(' >> qi::char_("0-9") >> ')', qi::space, parsed_char);

这将简单地绑定(bind) char_ 的公开属性 属性引用 ( parsed_char ) 的解析器组件传递到variadic 解析 API ( phrase_parse )。

下面是一个概括性的演示，展示了您可以通过多种方式来影响具体暴露的内容。解析器指令记录了确切暴露的内容，例如here, for the '%' list parser .

对于您的具体问题，您只想:

qi::rule<Iterator, char()> character;
qi::rule<Iterator, char()> parenthesized;

character     = qi::char_("0-9a-z_"); // or qi::alnum, qi::graph, qi::alpha etc...
parenthesized = '(' >> character >> ')';

Note importantly, you need to say qi::rule<Iterator, char()> instead of qi::rule<Iterator, char>!

演示

查看 Live on Coliru :

#include <boost/spirit/include/qi.hpp>
#include <cassert>

namespace qi = boost::spirit::qi;

template<typename ParseExpr, typename... Attr>
void test(const std::string& input, const ParseExpr& p, Attr&... attrs)
{
    auto f = input.begin(), 
         l = input.end();

    bool ok = qi::phrase_parse(f,l, p, qi::space, attrs...);

    if (!ok)
        std::cerr << "parse failed at: '" << std::string(f,l) << "'\n";

    if (f!=l) 
        std::cerr << "trailing unparsed: '" << std::string(f,l) << "'\n";
}

int main()
{
    char parsed_char1, parsed_char2;
    int parsed_int;
    std::string parsed_str;

    test("( 0 )",                        // input
         '(' >> qi::char_("0-9") >> ')', // parser/grammar
         parsed_char1                     // output
    );
    assert(parsed_char1 == '0');

    test("( q 123 )", 
            '(' >> qi::graph >> qi::int_ >> ')', 
            parsed_char1, 
            parsed_int);
    assert(parsed_char1 == 'q');
    assert(parsed_int == 123);

    // parsing strings: with the skipper
    test("( hello world )", 
        '(' >> *~qi::char_(")") >> ')', 
        parsed_str = "");
    assert(parsed_str == "helloworld");

    // parsing strings: qi::char_ exposes the char
    test("( hello world )", 
        qi::char_('(') >>  *~qi::char_(")") >> qi::char_(')'), 
        parsed_char1, parsed_str = "", parsed_char2);
    assert(parsed_char1 == '(');
    assert(parsed_str == "helloworld");
    assert(parsed_char2 == ')');

    // parsing strings: qi::char_ exposes the char, chars get 'combined' into attribute
    test("( hello world )", 
        qi::char_('(') >>  *~qi::char_(")") >> qi::char_(')'), 
        parsed_str = "");
    assert(parsed_str == "(helloworld)");

    // parsing strings: as a lexeme
    test("( hello world )", 
        '(' >> qi::lexeme [ *~qi::char_(")") ] >> ')', 
        parsed_str = "");
    assert(parsed_str == "hello world ");

    // parsing strings: as bigger lexeme
    test("( hello world )", 
        qi::lexeme [ '(' >>  *~qi::char_(")") >> ')' ], 
        parsed_str = "");
    assert(parsed_str == " hello world ");

    // parsing anything as "raw" - exposes an iterator pair, but still 'converts' to a string!
    test("( hello 42 false )", 
        qi::raw [ '(' >>  qi::lexeme[*qi::graph] >> qi::int_ >> qi::bool_ >> ')' ], 
        parsed_str = "");
    assert(parsed_str == "( hello 42 false )");

    // note: this would fail to parse, because with the skipper, *qi::graph would eat "42 false )" as well:
    std::cout << "next parse should fail:\n";
    test("( hello 42 false )", qi::raw [ '(' >>  *qi::graph >> qi::int_ >> qi::bool_ >> ')' ]);
}