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# std::ratio_subtract

From cppreference.com
< cpp‎ | numeric‎ | ratio

Defined in header `<ratio>` |  |
template< class R1, class R2 > using ratio_subtract = /* unspecified */; |  |

The template alias `std::ratio_subtract` denotes the result of subtracting two exact rational fractions represented by the std::ratio instances `R1` and `R2`. The result a std::ratio instance `std::ratio<Num, Denom>` where Num == R1::num * R2::den - R2::num * R1::den and Denom == R1::den * R2::den.

### [edit] Member types

Member type | Definition
`type` | std::ratio<num, den>

### [edit] Member constants

num [static] | constexpr value of type std::intmax_t equal to `sign(Num) * sign(Denom) * abs(Num) / gcd(Num, Denom)` (public static member constant)
den [static] | constexpr value of type std::intmax_t equal to `abs(Denom) / gcd(Num, Denom)` (public static member constant)

### [edit] Example

Run this code

    #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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