Defined in header `<ratio>` | ||
---|---|---|

template< class R1, class R2 > using ratio_subtract = /* see below */; |

The alias template `std::ratio_subtract`

denotes the result of subtracting two exact rational fractions represented by the `std::ratio`

specializations `R1`

and `R2`

.

The result is a `std::ratio`

specialization `std::ratio<U, V>`

, such that given `Num == R1::num * R2::den - R2::num * R1::den`

and `Denom == R1::den * R2::den`

(computed without arithmetic overflow), `U`

is `std::ratio<Num, Denom>::num`

and `V`

is `std::ratio<Num, Denom>::den`

.

If `U`

or `V`

is not representable in `std::intmax_t`

, the program is ill-formed. If `Num`

or `Denom`

is not representable in `std::intmax_t`

, the program is ill-formed unless the implementation yields correct values for `U`

and `V`

.

The above definition requires that the result of `std::ratio_subtract<R1, R2>`

be already reduced to lowest terms; for example, `std::ratio_subtract<std::ratio<1, 2>, std::ratio<1, 6>>`

is the same type as `std::ratio<1, 3>`

.

#include <iostream> #include <ratio> int main() { typedef std::ratio<2, 3> two_third; typedef std::ratio<1, 6> one_sixth; typedef std::ratio_subtract<two_third, one_sixth> diff; std::cout << "2/3 - 1/6 = " << diff::num << '/' << diff::den << '\n'; }

Output:

2/3 - 1/6 = 1/2

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