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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. int main()
  6. {
  7.     const std::string INPUT_DATA = "12e-1 + 3.4 - .67";
  8.     typedef std::string::const_iterator iterator_type;
  9.     iterator_type begin = std::begin(INPUT_DATA);
  10.     iterator_type end   = std::end(INPUT_DATA);
  11.  
  12.     namespace qi    = boost::spirit::qi;
  13.     namespace ascii = boost::spirit::qi::ascii;
  14.     namespace phx   = boost::phoenix;
  15.  
  16.     bool ok;
  17.     double result;
  18.     {
  19.         using namespace qi;
  20.  
  21.         auto parser = 
  22.                double_                  [_val  = _1]      // (1)
  23.             >> *(   (lit('+') >> double_[_val += _1])     // (2)
  24.                   | (lit('-') >> double_[_val -= _1])     // (3)
  25.                 );
  26.  
  27.         ok = phrase_parse(begin, end, parser, ascii::space, result);
  28.     }
  29.  
  30.     if (ok  && begin == end)
  31.         std::cout << "parsed, result = " << result << std::endl;
  32.     else
  33.         std::cout << "not parsed" << std::endl;
  34. }
  35.  
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https://ideone.com/HD4Vj8
language:
C++14 (gcc 8.3)
created:
10 years ago
visibility:
secret

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