将解析结果自动连接到向量中

auto concatenation of parse results into vectors

本文关键字：连接 向量 结果      更新时间：2023-10-16

我已经编写了一些规则，将浮点解析为两个std:：vector的浮点，然后将其存储在struct:中

数据输入：

#
# object name01
#
v  -1.5701 33.8087 0.3592
v  -24.0119 0.0050 21.7439
# a comment
vn 0.0000 0.5346 0.8451
vn 0.8331 0.5531 -0.0000
# another comment

结构：

struct ObjParseData
{
    ObjParseData() : verts(), norms() {}
    std::vector<float> verts;
    std::vector<float> norms;
};

以及相关解析代码：

struct objGram : qi::grammar<std::string::const_iterator, ObjParseData(), iso8859::space_type>
    {
        objGram() : objGram::base_type(start)
        {
            vertex  = 'v' >> qi::double_ >> qi::double_ >> qi::double_;
            normal  = "vn" >> qi::double_ >> qi::double_ >> qi::double_;
            comment = '#' >> qi::skip(qi::blank)[ *(qi::print) ];
            vertexList = *(vertex | comment);
            normalList = *(normal | comment);
            start = vertexList >> normalList;
        }
        qi::rule<std::string::const_iterator, ObjParseData(), iso8859::space_type> start;
        qi::rule<std::string::const_iterator, std::vector<float>(), iso8859::space_type> vertexList;
        qi::rule<std::string::const_iterator, std::vector<float>(), iso8859::space_type> normalList;
        qi::rule<std::string::const_iterator, std::vector<float>(), iso8859::space_type> vertex;
        qi::rule<std::string::const_iterator, std::vector<float>(), iso8859::space_type> normal;
        qi::rule<std::string::const_iterator, iso8859::space_type> comment;
    } objGrammar;

    ObjParseData resultData;
    std::string::const_iterator f = data.cbegin();
    bool res = qi::phrase_parse( f, data.cend(), objGrammar, iso8859::space, resultData );

这是有效的。它将所有以"v"开头的浮点数解析为结构的verts向量，并将所有以"vn"开头的浮数解析为范数。这很好，但我真的不知道为什么这样有效。

现在，如果我正确理解了这一点，下面定义的规则会将其所有结果放入一个std：：向量的float中。

qi::rule<std::string::const_iterator, std::vector<float>(), iso8859::space_type> vertex;

所以，看看上面显示的解析代码，知道像vertex这样的规则会解析成一个std:：vector of float，显然像vertex List这样的规则（上面显示的那个）会将来自vertex的结果连接成一个std：：vector的float？所以看到这种行为，你会认为你可以把这两个规则（顶点和顶点列表）写为一个，但不幸的是，这不起作用：

vertex  = *('v' >> qi::double_ >> qi::double_ >> qi::double_) | comment;
normal  = *("vn" >> qi::double_ >> qi::double_ >> qi::double_) | comment;
comment = '#' >> qi::skip(qi::blank)[ *(qi::print) ];
start = vertex >> normal;

代码确实进行了编译，qi:：phrase_parse确实返回了一个成功的解析，但结构中的std:：vector不再被填充。。我在这里错过了什么？

您错放了分组括号：展开

    vertexList = *(vertex | comment);
    normalList = *(normal | comment);

通过消除导致的子规则

    vertex     = *(('v'  >> qi::double_ >> qi::double_ >> qi::double_) | comment);
    normal     = *(("vn" >> qi::double_ >> qi::double_ >> qi::double_) | comment);

或者，我更喜欢：

完整的工作样本（请下次让您的代码样本SSCCE？https://meta.stackexchange.com/questions/22754/sscce-how-to-provide-examples-for-programming-questions)：

#include <iterator>
#include <fstream>
#include <boost/fusion/adapted.hpp>
#include <boost/spirit/include/qi.hpp>
#include <boost/spirit/include/karma.hpp>
#include <boost/spirit/include/phoenix.hpp>
namespace qi    = boost::spirit::qi;
namespace karma = boost::spirit::karma;
namespace phx   = boost::phoenix;
struct ObjParseData
{
    ObjParseData() : verts(), norms() {}
    std::vector<float> verts;
    std::vector<float> norms;
};
BOOST_FUSION_ADAPT_STRUCT(ObjParseData, (std::vector<float>, verts)(std::vector<float>, norms))

template <typename It, typename Skipper = qi::space_type>
    struct parser : qi::grammar<It, ObjParseData(), Skipper>
{
    parser() : parser::base_type(start)
    {
        using namespace qi;

        vertex     = 'v'  >> qi::double_ >> qi::double_ >> qi::double_;
        normal     = "vn" >> qi::double_ >> qi::double_ >> qi::double_;
        comment    = '#' >> qi::skip(qi::blank)[ *(qi::print) ];
#if 0
        vertexList = *(vertex | comment);
        normalList = *(normal | comment);
        start      = vertexList >> normalList;
#else
        vertex     = *(comment | ('v'  >> qi::double_ >> qi::double_ >> qi::double_));
        normal     = *(comment | ("vn" >> qi::double_ >> qi::double_ >> qi::double_));
        start      = vertex >> normal;                                              
#endif
        BOOST_SPIRIT_DEBUG_NODE(start);
    }
  private:
    qi::rule<std::string::const_iterator, ObjParseData(), qi::space_type> start;
    qi::rule<std::string::const_iterator, std::vector<float>(), qi::space_type> vertexList;
    qi::rule<std::string::const_iterator, std::vector<float>(), qi::space_type> normalList;
    qi::rule<std::string::const_iterator, std::vector<float>(), qi::space_type> vertex;
    qi::rule<std::string::const_iterator, std::vector<float>(), qi::space_type> normal;
    qi::rule<std::string::const_iterator, qi::space_type> comment;
};
bool doParse(const std::string& input)
{
    typedef std::string::const_iterator It;
    auto f(begin(input)), l(end(input));
    parser<It, qi::space_type> p;
    ObjParseData data;
    try
    {
        bool ok = qi::phrase_parse(f,l,p,qi::space,data);
        if (ok)   
        {
            std::cout << "parse successn";
            std::cout << "data: " << karma::format_delimited(
                    "v: " << karma::auto_ << karma::eol <<
                    "n: " << karma::auto_ << karma::eol, ' ', data);
        }
        else      std::cerr << "parse failed: '" << std::string(f,l) << "'n";
        if (f!=l) std::cerr << "trailing unparsed: '" << std::string(f,l) << "'n";
        return ok;
    } catch(const qi::expectation_failure<It>& e)
    {
        std::string frag(e.first, e.last);
        std::cerr << e.what() << "'" << frag << "'n";
    }
    return false;
}
int main()
{
    std::ifstream ifs("input.txt", std::ios::binary);
    ifs.unsetf(std::ios::skipws);
    std::istreambuf_iterator<char> f(ifs), l;
    bool ok = doParse({ f, l });
}

输出：

parse success
data: v:  -1.57 33.809 0.359 -24.012 0.005 21.744 
 n:  0.0 0.535 0.845 0.833 0.553 0.0
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