std::ratio_multiply(3)

NAME
std::ratio_multiply - std::ratio_multiply

Synopsis
   Defined in header <ratio>
   template< class R1, class R2 > (since C++11)
   using ratio_multiply = /* see below */;
   The alias template std::ratio_multiply denotes the result of multiplying 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::num 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_multiply<R1, R2> be
   already reduced to lowest terms; for example, std::ratio_multiply<std::ratio<1, 6>,
   std::ratio<4, 5>> is the same type as std::ratio<2, 15>.

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 product = std::ratio_multiply<two_third, one_sixth>;
     static_assert(std::ratio_equal_v<product, std::ratio<13, 117>>);
     std::cout << "2/3 * 1/6 = " << product::num << '/' << product::den << '\n';
 }

Output:
 2/3 * 1/6 = 1/9

See also
   ratio_divide divides two ratio objects at compile-time
   (C++11) (alias template)