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std::lcm

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.

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	Value	Std	Comment
`__cpp_lib_gcd_lcm`	201606L	(C++17)	`std::gcd`, `std::lcm`

Example

#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