The class templatestd::ratio providescompile-time rational arithmetic support. Each instantiation of this template exactly represents any finite rational number as long as its numeratorNum and denominatorDenom are representable as compile-time constants of typestd::intmax_t. In addition,Denom may not be zero and bothNum andDenom may not be equal to the most negative value.

The static data membersnum andden representing the numerator and denominator are calculated by dividingNum andDenom by their greatest common divisor. However, twostd::ratio with differentNum orDenom are distinct types even if they represent the same rational number (after reduction). Astd::ratio type can be reduced to the lowest terms via itstype member:std::ratio<3,6>::type isstd::ratio<1,2>.

The following convenience typedefs that correspond to the SI ratios are provided by the standard library:

1. ↑^1.01.11.21.3These typedefs are only declared ifstd::intmax_t can represent the denominator.
2. ↑^2.02.12.22.3These typedefs are only declared ifstd::intmax_t can represent the numerator.

[edit]Nested types

[edit]Data members

In the definitions given below,

• sign(Denom) is-1 ifDenom is negative, or1 otherwise; and
• gcd(Num, Denom) is the greatest common divisor ofstd::abs(Num) andstd::abs(Denom).

[edit]Notes

[edit]Example

#include <ratio> static_assert(std::ratio_equal_v<std::ratio_multiply<std::femto, std::exa>, std::kilo>); int main(){}

[edit]See also

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