std::ratio - Man Page

typedef ratio< num, den > type

static constexpr intmax_t den
static constexpr intmax_t num

struct std::ratio< _Num, _Den >"Provides compile-time rational arithmetic.

This class template represents any finite rational number with a numerator and denominator representable by compile-time constants of type intmax_t. The ratio is simplified when instantiated.

For example:

std::ratio<7,-21>::num == -1;
std::ratio<7,-21>::den == 3;