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:	`__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

Compiler support
Freestanding and hosted
Language
Standard library headers
Named requirements
Feature test macros (C++20)
Language support library
Concepts library (C++20)
Metaprogramming library (C++11)
Diagnostics library
General utilities library
Strings library
Containers library
Iterators library
Ranges library (C++20)
Algorithms library
Numerics library
Localizations library
Input/output library
Filesystem library (C++17)
Regular expressions library (C++11)
Concurrency support library (C++11)
Technical specifications
Symbols index
External libraries

Common mathematical functions
Mathematical special functions (C++17)
Mathematical constants (C++20)
Floating-point environment (C++11)
Complex numbers
Numeric arrays
Pseudo-random number generation
Factor operations
gcd (C++17)
lcm (C++17)
Interpolations
midpoint (C++20)
lerp (C++20)
Generic numeric operations
iota (C++11)
ranges::iota (C++23)
accumulate
inner_product
adjacent_difference
partial_sum
reduce (C++17)
transform_reduce (C++17)
inclusive_scan (C++17)
exclusive_scan (C++17)
transform_inclusive_scan (C++17)
transform_exclusive_scan (C++17)
Bit operations
bit_cast (C++20)
byteswap (C++23)
has_single_bit (C++20)
bit_ceil (C++20)
bit_floor (C++20)
bit_width (C++20)
rotl (C++20)
rotr (C++20)
countl_zero (C++20)
countl_one (C++20)
countr_zero (C++20)
countr_one (C++20)
popcount (C++20)
endian (C++20)