std::lcm

 

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

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 (C++17)

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