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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. #include <boost/phoenix/function/adapt_function.hpp>
  5.  
  6. struct add_operand { 
  7.     template<typename...> struct result { typedef void type; };
  8.     template<typename L, typename R>
  9.     void operator()(L& lhs, R rhs) const { lhs += rhs; } 
  10. };
  11.  
  12. struct sub_operand { 
  13.     template<typename...> struct result { typedef void type; };
  14.     template<typename L, typename R>
  15.     void operator()(L& lhs, R rhs) const { lhs -= rhs; } 
  16. };
  17.  
  18. int main()
  19. {
  20.     const std::string INPUT_DATA = "12e-1 + 3.4 - .67";
  21.     typedef std::string::const_iterator iterator_type;
  22.     iterator_type begin = std::begin(INPUT_DATA);
  23.     iterator_type end   = std::end(INPUT_DATA);
  24.  
  25.     namespace qi    = boost::spirit::qi;
  26.     namespace ascii = boost::spirit::qi::ascii;
  27.     namespace phx   = boost::phoenix;
  28.  
  29.     bool ok;
  30.     double result;
  31.     {
  32.         using namespace qi;
  33.         using phx::bind;
  34.  
  35.         auto parser = 
  36.                double_                  [_val  = _1]
  37.             >> *(   (lit('+') >> double_[bind(add_operand(), _val, _1)])
  38.                   | (lit('-') >> double_[bind(sub_operand(), _val, _1)])
  39.                 );
  40.  
  41.         ok = phrase_parse(begin, end, parser, ascii::space, result);
  42.     }
  43.  
  44.     if (ok  && begin == end)
  45.         std::cout << "parsed, result = " << result << std::endl;
  46.     else
  47.         std::cout << "not parsed" << std::endl;
  48. }
  49.  
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https://ideone.com/WA6nwg
language:
C++14 (gcc 8.3)
created:
10 years ago
visibility:
secret

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