使用 Boost.Spirit.Qi 捕获字符串直到行尾

Question

我正在尝试编写一个自定义结构来捕获字符串，直到 EOL 或 EOS 作为更大语法的一部分，但我无法编译它。我关注了tutorial code，但我无法在下面的 sn-p 中找出错误。

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

#include <string>
#include <cassert>

namespace qi = boost::spirit::qi;

namespace project {

struct RawValue {
    std::string str;
};

}

BOOST_FUSION_ADAPT_STRUCT(project::RawValue, str)

namespace project::parser {

struct RawValueParser : qi::grammar<std::string::const_iterator, RawValue(), qi::space_type> {
  RawValueParser() : RawValueParser::base_type(expr) {
    using qi::blank;
    using qi::char_;
    using qi::eol;
    using qi::lexeme;

    expr %= lexeme[*(char_ - eol) >> (char_ - blank)];
  }

  qi::rule<iterator_type, RawValue(), skipper_type> expr;
};

}

int main() {
  project::parser::RawValueParser expr;
  project::RawValue result;
  std::string s1 = "test1";
  auto iter = s1.cbegin();
  auto end = s1.cend();
  assert(qi::phrase_parse(iter, end, expr, qi::space, result));
  return 0;
}

https://wandbox.org/permlink/PjaaYwO0Qz18998y

这应该是一个相当简单的例子。我做错了什么？

Answer 1

编译错误源自这里：

test.cpp|21 col 58| required from here
/home/sehe/custom/spirit/include/boost/spirit/home/qi/nonterminal/grammar.hpp|77 col 13| error: static assertion failed: incompatible_start_rule
||    77 |             BOOST_SPIRIT_ASSERT_MSG(
||       |             ^~~~~~~~~~~~~~~~~~~~~~~

如果您前往指定位置（另请参阅How do I grok boost spirit compiler errors）：

// If you see the assertion below failing then the start rule
// passed to the constructor of the grammar is not compatible with
// the grammar (i.e. it uses different template parameters).
BOOST_SPIRIT_ASSERT_MSG(
    (is_same<start_type, rule<Iterator_, T1_, T2_, T3_, T4_> >::value)
  , incompatible_start_rule, (rule<Iterator_, T1_, T2_, T3_, T4_>));

那是你的问题。语法是<It, RawValue(), qi::space_type>，但起始规则是<iterator_type, RawValue(), skipper_type>，其中

    static_assert(std::is_same_v<It, iterator_type>);
    static_assert(std::is_same_v<qi::space_type, skipper_type>);
    qi::space_type _y = skipper_type{};

显示第二个断言失败。第三行导致更详细的诊断：Live

test.cpp|33 col 29| error: could not convert ‘boost::spirit::qi::grammar<__gnu_cxx::__normal_iterator<const char*, std::__cxx11::basic_string<char> >, project::RawValue(), boost::proto::exprns_::expr<boost::proto::tagns_::tag::terminal, boost::proto::argsns_::term<boost::spirit::tag::char_code<boost::spirit::tag::space, boost::spirit::char_encoding::standard> >, 0> >::skipper_type{}’ from ‘boost::spirit::qi::grammar<__gnu_cxx::__normal_iterator<const char*, std::__cxx11::basic_string<char> >, project::RawValue(), boost::proto::exprns_::expr<boost::proto::tagns_::tag::terminal, boost::proto::argsns_::term<boost::spirit::tag::char_code<boost::spirit::tag::space, boost::spirit::char_encoding::standard> >, 0> >::skipper_type’ {aka ‘boost::spirit::qi::char_class<boost::spirit::tag::char_code<boost::spirit::tag::space, boost::spirit::char_encoding::standard> >’} to ‘boost::spirit::standard::space_type’ {aka ‘boost::proto::exprns_::expr<boost::proto::tagns_::tag::terminal, boost::proto::argsns_::te
||    33 |         qi::space_type _y = skipper_type{};
||       |                             ^~~~~~~~~~~~~~
||       |                             |
||       |                             boost::spirit::qi::grammar<__gnu_cxx::__normal_iterator<const char*, std::__cxx11::basic_string<char> >, project::RawValue(), boost::proto::exprns_::expr<boost::proto::tagns_::tag::terminal, boost::proto::argsns_::term<boost::spirit::tag::char_code<boost::spirit::tag::space, boost::spirit::char_encoding::standard> >, 0> >::skipper_type {aka boost::spirit::qi::char_class<boost::spirit::tag::char_code<boost::spirit::tag::space, boost::spirit::char_encoding::standard> >}

您可以将整个事情分开，但只要说您认为skipper_type 等于第三个模板参数的假设是错误的就足够了。

只需拼出您期望的类型：Live

qi::rule<It, RawValue(), qi::space_type> expr;

附注

1. lexeme 禁用船长。考虑到简化整个事情：Live（另见Boost spirit skipper issues）

2. operator %= 没有语义动作就没有意义

3. expr 似乎用词不当

4. 否定字符类比减法解析器更有效；你的意思是(char_ - blank) 比eol 更有意义吗？

5. 现在不接受输入结尾而不是 eol。也许你应该允许它。我会这样写

   start = *~qi::char_("\n\r") >> (eol | eoi);
   

简化列表

Live On Coliru

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

#include <iomanip>

namespace qi = boost::spirit::qi;
using It = std::string::const_iterator;

struct RawValue { std::string str; };

BOOST_FUSION_ADAPT_STRUCT(RawValue, str)

struct RawValueParser : qi::grammar<It, RawValue()> {
    RawValueParser() : RawValueParser::base_type(start)
    {
        using namespace qi;
        start = *~qi::char_("\n\r") >> (eol | eoi);
    }

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

int main() {
    RawValueParser expr;

    for (std::string const s : {
             "test1",
             " test2\tbla   \n",
         }) {

        RawValue result;
        std::cout
            << std::boolalpha
            //<< qi::phrase_parse(begin(s), end(s), expr, qi::space, result)
            << qi::parse(begin(s), end(s), expr, result) << " -> "
            << std::quoted(result.str) << "\n";
    }
}

打印

true -> "test1"
true -> " test2 bla   "