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  1. #define BOOST_SPIRIT_USE_PHOENIX_V3
  2. #include <boost/spirit/include/qi.hpp>
  3. #include <boost/spirit/include/phoenix.hpp>
  4.  
  5. void add_operand(double& lhs, double rhs) { lhs += rhs; }
  6. void sub_operand(double& lhs, double rhs) { lhs -= rhs; }
  7.  
  8. int main()
  9. {
  10.     const std::string INPUT_DATA = "12e-1 + 3.4 - .67";
  11.     typedef std::string::const_iterator iterator_type;
  12.     iterator_type begin = std::begin(INPUT_DATA);
  13.     iterator_type end   = std::end(INPUT_DATA);
  14.  
  15.     namespace qi    = boost::spirit::qi;
  16.     namespace ascii = boost::spirit::qi::ascii;
  17.     namespace phx   = boost::phoenix;
  18.  
  19.     bool ok;
  20.     double result;
  21.     {
  22.         using namespace qi;
  23.         using phx::bind;
  24.  
  25.         auto parser = 
  26.                double_                  [_val  = _1]
  27.             >> *(   (lit('+') >> double_[bind(add_operand, _val, _1)])
  28.                   | (lit('-') >> double_[bind(sub_operand, _val, _1)])
  29.                 );
  30.  
  31.         ok = phrase_parse(begin, end, parser, ascii::space, result);
  32.     }
  33.  
  34.     if (ok  && begin == end)
  35.         std::cout << "parsed, result = " << result << std::endl;
  36.     else
  37.         std::cout << "not parsed" << std::endl;
  38. }
  39.  
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https://ideone.com/u29r9G
language:
C++14 (gcc 8.3)
created:
11 years ago
visibility:
secret

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