std::ratio(3) C++ Standard Libary std::ratio(3) NAME std::ratio - std::ratio Synopsis Defined in header <ratio> template< std::intmax_t Num, (since C++11) std::intmax_t Denom = 1 > class ratio; The class template std::ratio provides compile-time rational arithmetic support. Each instantiation of this template exactly represents any finite ratio- nal number as long as its numerator Num and denominator Denom are representable as compile-time constants of type std::intmax_t. In addition, Denom may not be zero and both Num and Denom may not be equal to the most negative value. The static data members num and den representing the numerator and de- nominator are calculated by dividing Num and Denom by their greatest common divisor. However, two std::ratio with different Num or Denom are distinct types even if they represent the same rational number (after reduction). A std::ratio type can be reduced to the lowest terms via its type member: std::ratio<3, 6>::type is std::ra- tio<1, 2>. The following convenience typedefs that correspond to the SI ratios are provided by the standard library: Defined in header <ratio> Type Definition quecto (since C++26) std::ratio<1, 1000000000000000000000000000000> (10^-30)^[1] ronto (since C++26) std::ratio<1, 1000000000000000000000000000> (10^-27)^[1] yocto std::ratio<1, 1000000000000000000000000> (10^-24)^[1] zepto std::ratio<1, 1000000000000000000000> (10^-21)^[1] atto std::ratio<1, 1000000000000000000> (10^-18) femto std::ratio<1, 1000000000000000> (10^-15) pico std::ratio<1, 1000000000000> (10^-12) nano std::ratio<1, 1000000000> (10^-9) micro std::ratio<1, 1000000> (10^-6) milli std::ratio<1, 1000> (10^-3) centi std::ratio<1, 100> (10^-2) deci std::ratio<1, 10> (10^-1) deca std::ratio<10, 1> (10^1) hecto std::ratio<100, 1> (10^2) kilo std::ratio<1000, 1> (10^3) mega std::ratio<1000000, 1> (10^6) giga std::ratio<1000000000, 1> (10^9) tera std::ratio<1000000000000, 1> (10^12) peta std::ratio<1000000000000000, 1> (10^15) exa std::ratio<1000000000000000000, 1> (10^18) zetta std::ratio<1000000000000000000000, 1> (10^21)^[2] yotta std::ratio<1000000000000000000000000, 1> (10^24)^[2] ronna (since C++26) std::ratio<1000000000000000000000000000, 1> (10^27)^[2] quetta (since C++26) std::ratio<1000000000000000000000000000000, 1> (10^30)^[2] 1. a ^1.0 ^1.1 ^1.2 ^1.3 These typedefs are only defined if std::int- max_t can represent the denominator. 2. a ^2.0 ^2.1 ^2.2 ^2.3 These typedefs are only defined if std::int- max_t can represent the numerator. Notes Feature-test macro Value Std Feature __cpp_lib_ratio 202306L (C++26) Adding the new 2022 SI prefixes: quecto, quetta, ronto, ronna Example // Run this code #include <ratio> static_assert ( std::ratio_equal_v<std::ratio_multiply<std::femto, std::exa>, std::kilo> ); int main() {} See also Mathematical constants (C++20) provides several mathematical constants, such as std::numbers::e for e http://cppreference.com 2024.06.10 std::ratio(3)
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