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

From cppreference.com
< cpp‎ | chrono‎ | month
C++
Date and time library
Time point
(C++11)
(C++20)
Duration
(C++11)
Clocks
(C++11)
(C++11)
(C++20)
(C++20)
(C++20)
(C++11)
(C++20)
(C++20)
(C++20)
Time of day
(C++20)(C++20)
(C++20)(C++20)
(C++20)

Calendar
(C++20)
(C++20)
(C++20)
(C++20)
(C++20)
(C++20)
(C++20)
(C++20)
(C++20)
(C++20)
(C++20)(C++20)
Time zone
(C++20)
(C++20)
(C++20) (C++20) (C++20) (C++20)
(C++20)
(C++20)
(C++20)
(C++20)
(C++20)
(C++20)
(C++20)
(C++20)
chrono I/O
(C++20)
C-style date and time
std::chrono::month
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

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

 increments or decrements the month
(public member function)
(C++20)
 performs arithmetic on months
(function)
Retrieved from "https://en.cppreference.com/mwiki/index.php?title=cpp/chrono/month/operator_arith&oldid=157580