std::chrono::year_month_day::operator+=, std::chrono::year_month_day::operator-=
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std::chrono::year_month_day
Member functions
year_month_day::operator+=year_month_day::operator-=
Nonmember functions
Helper classes
constexpr std::chrono::year_month_day &
operator+=( const std::chrono::years & dy ) const noexcept;
(1)
(since C++20)
operator+=( const std::chrono::years & dy ) const noexcept;
constexpr std::chrono::year_month_day &
operator+=( const std::chrono::months & dm ) const noexcept;
(2)
(since C++20)
operator+=( const std::chrono::months & dm ) const noexcept;
constexpr std::chrono::year_month_day &
operator-=( const std::chrono::years & dy ) const noexcept;
(3)
(since C++20)
operator-=( const std::chrono::years & dy ) const noexcept;
constexpr std::chrono::year_month_day &
operator-=( const std::chrono::months & dm ) const noexcept;
(4)
(since C++20)
operator-=( const std::chrono::months & dm ) const noexcept;
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.
[edit] 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年07月01日 #2 2010年07月01日 #3 2021年06月01日 #4 2021年05月31日 #5 2021-06-31 is not a valid date #6 2021/Jun/last #7 2021年07月01日