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

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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 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

increments or decrements the month
(public member function)
(C++20)
performs arithmetic on month s
(function)
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