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

 

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C-style date and time

 

std::chrono::month

Member functions

month::month

month::operator++month::operator--

month::operator+=month::operator-=

month::operator unsigned

month::ok

Nonmember functions

operator==operator<=>

operator+operator-

operator<<

from_stream

Helper classes

formatter<std::chrono::month>

hash<std::chrono::month> (C++26)

 

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

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