Standard library header <ratio>
From cppreference.com
                    
                                        
                    
                    
                                                            
                    This header is part of the compile-time rational arithmetic library.
 
 Classes | 
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|    represents exact rational fraction  (class template)  | 
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 Arithmetic | 
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|    (C++11) 
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   adds two ratio objects at compile-time  (alias template)  | 
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|    (C++11) 
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   subtracts two ratio objects at compile-time  (alias template)  | 
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|    (C++11) 
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   multiplies two ratio objects at compile-time  (alias template)  | 
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|    (C++11) 
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   divides two ratio objects at compile-time  (alias template)  | 
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 Comparison | 
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|    (C++11) 
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   compares two ratio objects for equality at compile-time  (class template)  | 
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|    (C++11) 
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   compares two ratio objects for inequality at compile-time  (class template)  | 
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|    (C++11) 
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   compares two ratio objects for less than at compile-time  (class template)  | 
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|    (C++11) 
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   compares two ratio objects for less than or equal to at compile-time (class template)  | 
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|    (C++11) 
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   compares two ratio objects for greater than at compile-time  (class template)  | 
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|    (C++11) 
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   compares two ratio objects for greater than or equal to at compile-time  (class template)  | 
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 Constants | 
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  yocto
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std::ratio<1, 1000000000000000000000000>, if std::intmax_t can represent the denominator | |
  zepto
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std::ratio<1, 1000000000000000000000>, if std::intmax_t can represent the denominator | |
  atto
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std::ratio<1, 1000000000000000000> | |
  femto
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std::ratio<1, 1000000000000000> | |
  pico
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std::ratio<1, 1000000000000> | |
  nano
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std::ratio<1, 1000000000> | |
  micro
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std::ratio<1, 1000000> | |
  milli
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std::ratio<1, 1000> | |
  centi
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std::ratio<1, 100> | |
  deci
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std::ratio<1, 10> | |
  deca
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std::ratio<10, 1> | |
  hecto
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std::ratio<100, 1> | |
  kilo
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std::ratio<1000, 1> | |
  mega
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std::ratio<1000000, 1> | |
  giga
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std::ratio<1000000000, 1> | |
  tera
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std::ratio<1000000000000, 1> | |
  peta
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std::ratio<1000000000000000, 1> | |
  exa
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std::ratio<1000000000000000000, 1> | |
  zetta
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std::ratio<1000000000000000000000, 1>, if std::intmax_t can represent the numerator | |
  yotta
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std::ratio<1000000000000000000000000, 1>, if std::intmax_t can represent the numerator | |
namespace std { //class template ratio template <intmax_t N, intmax_t D = 1> class ratio { public: typedef ratio<num, den> type; static constexpr intmax_t num; static constexpr intmax_t den; }; // ratio arithmetic template <class R1, class R2> using ratio_add = /*ratio*/; template <class R1, class R2> using ratio_subtract = /*ratio*/; template <class R1, class R2> using ratio_multiply = /*ratio*/; template <class R1, class R2> using ratio_divide = /*ratio*/; // ratio comparison template <class R1, class R2> struct ratio_equal; template <class R1, class R2> struct ratio_not_equal; template <class R1, class R2> struct ratio_less; template <class R1, class R2> struct ratio_less_equal; template <class R1, class R2> struct ratio_greater; template <class R1, class R2> struct ratio_greater_equal; // convenience SI typedefs typedef ratio<1, 1000000000000000000000000> yocto; typedef ratio<1, 1000000000000000000000> zepto; typedef ratio<1, 1000000000000000000> atto; typedef ratio<1, 1000000000000000> femto; typedef ratio<1, 1000000000000> pico; typedef ratio<1, 1000000000> nano; typedef ratio<1, 1000000> micro; typedef ratio<1, 1000> milli; typedef ratio<1, 100> centi; typedef ratio<1, 10> deci; typedef ratio< 10, 1> deca; typedef ratio< 100, 1> hecto; typedef ratio< 1000, 1> kilo; typedef ratio< 1000000, 1> mega; typedef ratio< 1000000000, 1> giga; typedef ratio< 1000000000000, 1> tera; typedef ratio< 1000000000000000, 1> peta; typedef ratio< 1000000000000000000, 1> exa; typedef ratio< 1000000000000000000000, 1> zetta; typedef ratio<1000000000000000000000000, 1> yotta; }