Boost::Spirit::QI 解析器:解析元素的索引 [英] Boost::Spirit::QI parser: index of parsed element

问题描述

是否可以(使用 Boost::Spirit::QI)从逗号分隔的字符串中解析数字，以便获得每个解析数字的索引?

假设我有一个字符串 "23,123,65,1" 并且我想将这些数字中的每一个插入到给定位置 (0, 1, 2, 3) 的矩阵中.一种方法是将数字解析为 std::vector，然后将它们复制到矩阵行，但速度不是特别快.

目前我正在使用矢量变体:

矩阵数据(10, 4);整数行 = 0;int col = 0;std::string str = "23,123,65,1";std::vector资源；if (qi::parse(str.begin(), str.end(), qi::double_ % ',', res)){std::for_each(res.begin(), res.end(), [&col, &data, &row](double elem) {数据(行，列)= elem；颜色++;});}

如果解析器有一个采用 lambda 函数或类似功能的成功回调，那就太棒了.

解决方案

有很多方法.

• 我通常推荐的做法是使用经过深思熟虑的repeat(n) 表达式，并直接暴露容器属性(如vector<;向量 >).

• 您似乎要寻找的是带有状态的语义动作.(这是来自 lex/yacc 的常见做法).

我在下面的三个完整演示中介绍了这些方法(1.、2. 和 3.)

• 一种高级技术是使用自定义点让 Spirit 直接将您的 Matrix 类型视为容器属性，并使用 spirit 覆盖它的插入逻辑::traits.对于这种方法，我参考了这个答案:pass attribute to孩子统治提振精神.

使用 继承属性

这是一个相对简单的方法:

1. 直接解析成vector;>(完整代码在线直播)

   qi::rule排;qi::rule矩阵;行 %= skip(char_(" 	,")) [ repeat(_r1) [ double_ ] ];矩阵 %= eps//[ std::cout <<phx::val("调试:") <<_r1<<", " <<_r2<<"
   " ]>>重复(_r1)[行(_r2)>>(eol|eoi) ];

   用法:

   if (qi::phrase_parse(f,l,parser(10, 4),qi::blank, m))std::cout <<"哇哦
   ";别的std::cerr <<"呃
   ";

2. 类似，但采用 Matrix 结构(完整代码住在这里)

   struct 矩阵{矩阵(size_t 行，size_t cols):_cells()，_rows(行)，_cols(cols){}双&数据(size_t col, size_t row) { return _cells.at(row).at(col);}const double &数据(size_t col, size_t row) const { return _cells.at(row).at(col);}size_t 列()const { 返回 _cols;}size_t 行()const { 返回 _rows；}std::vector>_细胞;size_t _rows, _cols;};BOOST_FUSION_ADAPT_STRUCT(矩阵，(std::vector >,_cells))

   用法

   矩阵 m(10, 4);如果 (qi::phrase_parse(f,l,parser(m.rows(),m.columns()),qi::blank, m))std::cout <<"哇哦
   ";别的std::cerr <<"呃
   ";

使用语义动作/qi::locals

3.这是更多的工作，但可能更灵活.您将定义一个多态可调用类型以在给定单元格中插入一个值:

struct MatrixInsert{模板<类型名，类型名，类型名，类型名>结构结果 { typedef bool 类型；};模板 <typename Matrix, typename Row, typename Col, typename Value>bool operator()(Matrix &m, Row& r, Col& c, Value v) const{if (r 

最后一行使它成为一个 phoenix 惰性函数，因此您可以在语义操作中使用它而无需奇怪的绑定语法:

qi::rule>矩阵;矩阵 = eps [ _a = 0/*当前行*/]>>(eps [ _b = 0/*当前列*/]>>double_ [ _pass = matrix_insert(_val, _a, _b, _1) ] % ',') % (eol [ ++_a/*下一行*/]);

完整代码再次liveworkspace.org

Is it possible (using Boost::Spirit::QI) to parse numbers from a comma separated string so that I get the index of each parsed number?

Suppose I have a string "23,123,65,1" and I want to insert each of these numbers into a matrix at given locations (0, 1, 2, 3). One way to do it would to parse the numbers into an std::vector and then copy them to the matrix row, but it isn't particularly fast.

Currently I'm using the vector variant:

Matrix data(10, 4);
int row = 0;
int col = 0;
std::string str = "23,123,65,1";
std::vector<double> res;
if (qi::parse(str.begin(), str.end(), qi::double_ % ',', res))
{
  std::for_each(res.begin(), res.end(), [&col, &data, &row](double elem) {

      data(row, col) = elem;
      col++;
});
}

It'd be awesome if the parser had a success callback that takes a lambda function or a similar feature.

解决方案

There are a number of approaches.

• What I'd usually recommend instead, is using well thought out repeat(n) expressions with directly exposed container attributes (like vector<vector<double> >).

• What you seem to be looking for is semantic actions with state. (This is common practice coming from lex/yacc).

I treat these approaches in three full demos below (1., 2. and 3.)

• An advanced technique is using customization points to allow Spirit to directly treat your Matrix type as a container attribute and override the insertion logic for it using spirit::traits. For this approach I refer to this answer: pass attribute to child rule in boost spirit.

Using inherited attributes

Here is a relatively straightforward approach:

1. parsing directly into a vector<vector<double> > (full code live online)

   qi::rule<It, Matrix::value_type(size_t cols), qi::blank_type> row;
   qi::rule<It, Matrix(size_t rows,size_t cols), qi::blank_type> matrix;
   
   row    %= skip(char_(" 	,")) [ repeat(_r1) [ double_ ] ];
   matrix %= eps // [ std::cout << phx::val("debug: ") << _r1 << ", " << _r2 << "
   " ]
          >> repeat(_r1) [ row(_r2) >> (eol|eoi) ];
   

   Usage:

   if (qi::phrase_parse(f,l,parser(10, 4),qi::blank, m))
       std::cout << "Wokay
   ";
   else
       std::cerr << "Uhoh
   ";
   

2. Similarly, but adapting a Matrix struct (full code live here)

   struct Matrix
   {
       Matrix(size_t rows, size_t cols) : _cells(), _rows(rows), _cols(cols) { }
   
       double       & data(size_t col, size_t row)       { return _cells.at(row).at(col); } 
       const double & data(size_t col, size_t row) const { return _cells.at(row).at(col); } 
   
       size_t columns() const { return _cols; }
       size_t rows()    const { return _rows; }
   
       std::vector<std::vector<double> > _cells;
       size_t _rows, _cols;
   };
   
   BOOST_FUSION_ADAPT_STRUCT(Matrix, (std::vector<std::vector<double> >,_cells))
   

   Usage

   Matrix m(10, 4);
   
   if (qi::phrase_parse(f,l,parser(m.rows(),m.columns()),qi::blank, m))
       std::cout << "Wokay
   ";
   else
       std::cerr << "Uhoh
   ";
   

Using semantic actions/qi::locals

3. This is more work, but potentially more flexible. You'd define a polymorphic callable type to insert a value at a given cell:

struct MatrixInsert
{
    template <typename, typename, typename, typename> struct result { typedef bool type; };
    template <typename Matrix, typename Row, typename Col, typename Value>
        bool operator()(Matrix &m, Row& r, Col& c, Value v) const
        {
            if (r < m.rows() && c < m.columns())
            {
                m.data(r, c++) = v;
                return true; // parse continues
            }
            return false;    // fail the parse
        }
};

BOOST_PHOENIX_ADAPT_CALLABLE(matrix_insert, MatrixInsert, 4)

The last line makes this a phoenix lazy function, so you can use it without weird bind syntax in your semantic actions:

qi::rule<It, Matrix(), qi::blank_type, qi::locals<size_t /*_a: row*/, size_t/*_b: col*/> > matrix;
matrix = eps    [ _a = 0 /*current row*/ ]
     >> (
            eps     [ _b = 0 /*current col*/ ] 
         >> double_ [ _pass = matrix_insert(_val, _a, _b, _1) ] % ','
        ) % (eol    [ ++_a /*next row*/])
     ;

Full code is, again live on liveworkspace.org

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