std::ratio_subtract(3)

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)