NAME¶

std::chrono::month::operator+=,std::chrono::month::operator-= - std::chrono::month::operator+=,std::chrono::month::operator-=

Synopsis¶

constexpr std::chrono::month& operator+=( const (1) (since C++20)
std::chrono::months& m ) noexcept;
constexpr std::chrono::month& operator-=( const (2) (since C++20)
std::chrono::months& m ) noexcept;

Adds or subtracts m.count() from the month value, reducing the result modulo 12 to
an integer in the range [1, 12].

1) Performs *this = *this + m;.
2) Performs *this = *this - m;.

Return value¶

A reference to this month after modification.

Notes¶

After a call to one of these functions, ok() is always true if no overflow occurred
during the operation.

Example¶

// Run this code

#include <chrono>
#include <iostream>

int main()
{
std::cout << std::boolalpha;

std::chrono::month m{6};
m += std::chrono::months(2);
std::cout << (m == std::chrono::month(8)) << ' '
<< (m == std::chrono::August) << ' ';

m -= std::chrono::months(3);
std::cout << (m == std::chrono::month(5)) << ' '
<< (m == std::chrono::May) << ' ';

m = std::chrono::October;
m += std::chrono::months{8}; // ((10 += 8 == 18) % 12) == 6;
std::cout << (m == std::chrono::June) << ' ';

m -= std::chrono::months{std::chrono::December - std::chrono::February}; // -= 10
// (6 -= 10) == -4; -4 % 12 == (12 - 4) == 8
std::cout << (m == std::chrono::August) << '\n';
}

Output:¶

true true true true true true

See also¶

operator++
operator++(int) increments or decrements the month
operator-- (public member function)
operator--(int)
operator+ performs arithmetic on months
operator- (function)
(C++20)