NAME¶

std::lcm - std::lcm

Synopsis¶

Defined in header <numeric>
template< class M, class N > (since C++17)
constexpr std::common_type_t<M, N> lcm( M m, N n );

Computes the least common multiple of the integers m and n.

Parameters¶

m, n - integer values

Return value¶

If either m or n is zero, returns zero. Otherwise, returns the least common multiple
of |m| and |n|.

Remarks

If either M or N is not an integer type, or if either is (possibly cv-qualified)
bool, the program is ill-formed.

The behavior is undefined if |m|, |n|, or the least common multiple of |m| and |n|
is not representable as a value of type std::common_type_t<M, N>.

Exceptions¶

Throws no exceptions.

Notes¶

Feature-test macro: __cpp_lib_gcd_lcm

Example¶

// Run this code

#include <numeric>
#include <iostream>

#define OUT(...) std::cout << #__VA_ARGS__ << " = " << __VA_ARGS__ << '\n'

constexpr auto lcm(auto x, auto y) {
return std::lcm(x,y);
}
constexpr auto lcm(auto head, auto...tail) {
return std::lcm(head, lcm(tail...));
}

int main() {
constexpr int p {2 * 2 * 3};
constexpr int q {2 * 3 * 3};
static_assert(2 * 2 * 3 * 3 == std::lcm(p, q));
static_assert(225 == std::lcm(45, 75));

OUT(lcm(2*3, 3*4, 4*5));
OUT(lcm(2*3*4, 3*4*5, 4*5*6));
OUT(lcm(2*3*4, 3*4*5, 4*5*6, 5*6*7));
}

Output:¶

lcm(2*3, 3*4, 4*5) = 60
lcm(2*3*4, 3*4*5, 4*5*6) = 120
lcm(2*3*4, 3*4*5, 4*5*6, 5*6*7) = 840

See also¶

gcd constexpr function template returning the greatest common divisor of two
(C++17) integers
(function template)