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

 

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C-style date and time

 

std::chrono::year_month_day

Member functions

year_month_day::year_month_day

year_month_day::operator+=year_month_day::operator-=

year_month_day::yearyear_month_day::monthyear_month_day::day

year_month_day::operator sys_daysyear_month_day::operator local_days

year_month_day::ok

Nonmember functions

operator==operator<=>

operator+operator-

operator<<

from_stream

Helper classes

formatter<std::chrono::year_month_day>

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

 

constexpr std::chrono::year_month_day&     operator+=( const std::chrono::years& dy ) const noexcept;	(1)	(since C++20)
constexpr std::chrono::year_month_day&     operator+=( const std::chrono::months& dm ) const noexcept;	(2)	(since C++20)
constexpr std::chrono::year_month_day&     operator-=( const std::chrono::years& dy ) const noexcept;	(3)	(since C++20)
constexpr std::chrono::year_month_day&     operator-=( const std::chrono::months& dm ) const noexcept;	(4)	(since C++20)

Modifies the time point *this represents by the duration dy or dm.

1) Equivalent to *this = *this + dy;.

2) Equivalent to *this = *this + dm;.

3) Equivalent to *this = *this - dy;.

4) Equivalent to *this = *this - dm;.

For durations that are convertible to both std::chrono::years and std::chrono::months, the years overloads (1,3) are preferred if the call would otherwise be ambiguous.

Example

Run this code

#include <cassert>
#include <chrono>
#include <iostream>
 
int main()
{
    constexpr auto monthsInYear{12};
    auto ymd{std::chrono::day(1)/std::chrono::July/2020};
    std::cout << "#1 " << ymd << '\n';
 
    ymd -= std::chrono::years(10);
    std::cout << "#2 " << ymd << '\n';
    assert(ymd.month() == std::chrono::July);
    assert(ymd.year() == std::chrono::year(2010));
 
    ymd += std::chrono::months(10 * monthsInYear + 11);
    std::cout << "#3 " << ymd << '\n';
    assert(ymd.month() == std::chrono::month(6));
    assert(ymd.year() == std::chrono::year(2021));
 
    // Handling the ymd += months "overflow" case.
    ymd = std::chrono::May/31/2021; // ok
    std::cout << "#4 " << ymd << '\n';
    assert(ymd.ok());
 
    ymd += std::chrono::months{1}; // bad date: June has only 30 days
    std::cout << "#5 " << ymd << '\n';
    assert(not ymd.ok());
    assert(ymd == std::chrono::June/31/2021);
 
    // Snap to the last day of the month, June 30:
    const auto ymd1 = ymd.year()/ymd.month()/std::chrono::last;
    std::cout << "#6 " << ymd1 << '\n';
    assert(ymd1.ok());
    assert(ymd1 == std::chrono::June/30/2021);
 
    // Overflow into the next month, July 1 (via converting to/from sys_days):
    const std::chrono::year_month_day ymd2 = std::chrono::sys_days{ymd};
    std::cout << "#7 " << ymd2 << '\n';
    assert(ymd2.ok());
    assert(ymd2 == std::chrono::July/1/2021);
}

Output:

#1 2020-07-01
#2 2010-07-01
#3 2021-06-01
#4 2021-05-31
#5 2021-06-31 is not a valid date
#6 2021/Jun/last
#7 2021-07-01

See also

operator+operator- (C++20)

adds or subtracts a year_month_day and some number of years or months (function)