提升精神解析 CSV，列顺序可变

我会同意你的想法，

我认为它非常优雅（齐当地人甚至允许重复使用这个）。

为了减少规则中的缺陷（Boost Spirit："语义行为是邪恶的"？），您可以将"转换函数"移至属性转换自定义点。

哎呀。正如评论的那样，这太简单了。但是，您仍然可以大大减少粗糙度。通过两个简单的调整，语法如下：

item.add("Name", NAME)("Age", AGE);
start  = omit[ header[_a=_1] ] >> eol >> line(_a) % eol;
header = (item | omit[column] >> attr(UNUSED)) % colsep;
line   = (column % colsep) [convert];
column = quoted | *~char_(",n");
quoted = '"' >> *("""" | ~char_(""n")) >> '"';

调整：

• 使用 qi::symbols 从标头映射到LineItem

• 使用直接访问上下文的原始语义操作（[convert]）（请参阅增强精神语义操作参数）：

  struct final {
      using Ctx = typename decltype(line)::context_type;
      void operator()(Columns const& columns, Ctx &ctx, bool &pass) const {
          auto& csvLine   = boost::fusion::at_c<0>(ctx.attributes);
          auto& positions = boost::fusion::at_c<1>(ctx.attributes);
          int i =0;
          for (LineItems position : positions) {
              switch (position) {
                  case NAME: csvLine.name = columns[i];              break;
                  case AGE:  csvLine.age = atoi(columns[i].c_str()); break;
                  default:   break;
              }
              i++;
          }
          pass = true; // returning false fails the `line` rule
      }
  } convert;
  

可以说，结果类似于做auto convert = phx::bind(&CsvGrammar<It>::convertFunc, this, qi::_1, qi::_r1, qi::_val)但是将auto与原始/凤凰/精神表达式一起使用是出了名的容易出错（UB 由于从表达式模板中悬挂对临时的引用），所以我当然更喜欢上面显示的方式。

住在科里鲁

//#define BOOST_SPIRIT_DEBUG
#define BOOST_SPIRIT_USE_PHOENIX_V3
#include <iostream>
#include <boost/fusion/include/at_c.hpp>
#include <boost/spirit/include/qi.hpp>
#include <boost/spirit/include/phoenix.hpp>
#include <string>
#include <vector>
namespace qi = boost::spirit::qi;
namespace phx = boost::phoenix;
using std::string;
enum LineItems { NAME, AGE, UNUSED };
struct CsvLine {
    string name;
    int age;
};
using Column  = std::string;
using Columns = std::vector<Column>;
using CsvFile = std::vector<CsvLine>;
template<typename It>
struct CsvGrammar: qi::grammar<It, CsvFile(), qi::locals<std::vector<LineItems>>, qi::blank_type> {
    CsvGrammar() : CsvGrammar::base_type(start) {
        using namespace qi;
        static const char colsep = ',';
        item.add("Name", NAME)("Age", AGE);
        start  = qi::omit[ header[_a=_1] ] >> eol >> line(_a) % eol;
        header = (item | omit[column] >> attr(UNUSED)) % colsep;
        line   = (column % colsep) [convert];
        column = quoted | *~char_(",n");
        quoted = '"' >> *("""" | ~char_(""n")) >> '"';
        BOOST_SPIRIT_DEBUG_NODES((header)(column)(quoted));
    }
private:
    qi::rule<It, std::vector<LineItems>(),                      qi::blank_type> header;
    qi::rule<It, CsvFile(), qi::locals<std::vector<LineItems>>, qi::blank_type> start;
    qi::rule<It, CsvLine(std::vector<LineItems> const&),        qi::blank_type> line;
    qi::rule<It, Column(), qi::blank_type> column;
    qi::rule<It, std::string()> quoted;
    qi::rule<It, qi::blank_type> empty;
    qi::symbols<char, LineItems> item;
    struct final {
        using Ctx = typename decltype(line)::context_type;
        void operator()(Columns const& columns, Ctx &ctx, bool &pass) const {
            auto& csvLine   = boost::fusion::at_c<0>(ctx.attributes);
            auto& positions = boost::fusion::at_c<1>(ctx.attributes);
            int i =0;
            for (LineItems position : positions) {
                switch (position) {
                    case NAME: csvLine.name = columns[i];              break;
                    case AGE:  csvLine.age = atoi(columns[i].c_str()); break;
                    default:   break;
                }
                i++;
            }
            pass = true; // returning false fails the `line` rule
        }
    } convert;
};
int main() {
    const std::string s = "Surname,Name,Age,nJohn,Doe,32nMark,Smith,43";
    auto f(begin(s)), l(end(s));
    CsvGrammar<std::string::const_iterator> p;
    CsvFile parsed;
    bool ok = qi::phrase_parse(f, l, p, qi::blank, parsed);
    if (ok) {
        for (CsvLine line : parsed) {
            std::cout << '[' << line.name << ']' << '[' << line.age << ']';
            std::cout << std::endl;
        }
    } else {
        std::cout << "Parse failedn";
    }
    if (f != l)
        std::cout << "Remaining unparsed: '" << std::string(f, l) << "'n";
}

指纹

[Doe][32]
[Smith][43]