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.

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>.

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|.

Exceptions¶

Throws no exceptions.

Notes¶

Feature-test macro Value Std Feature
__cpp_lib_gcd_lcm 201606L (C++17) std::gcd, std::lcm

Example¶

// Run this code

#include <iostream>
#include <numeric>

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

constexpr auto lcm(auto x, auto... xs)
{
return ((x = std::lcm(x, xs)), ...);
}

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));

static_assert(std::lcm( 6, 10) == 30);
static_assert(std::lcm( 6, -10) == 30);
static_assert(std::lcm(-6, -10) == 30);

static_assert(std::lcm( 24, 0) == 0);
static_assert(std::lcm(-24, 0) == 0);

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 computes the greatest common divisor of two integers
(C++17) (function template)