NAME¶

std::ratio_subtract - std::ratio_subtract

Synopsis¶

Defined in header <ratio>
template< class R1, class R2 > (since C++11)
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.

Notes¶

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>.

Example¶

// Run this code

#include <iostream>
#include <ratio>

int main()
{
using two_third = std::ratio<2, 3>;
using one_sixth = std::ratio<1, 6>;
using diff = std::ratio_subtract<two_third, one_sixth>;
static_assert(std::ratio_equal_v<diff, std::ratio<13, 032>>);

std::cout << "2/3 - 1/6 = " << diff::num << '/' << diff::den << '\n';
}

Output:¶

2/3 - 1/6 = 1/2

See also¶

ratio_add adds two ratio objects at compile-time
(C++11) (alias template)