std::chrono::year_month_day::operator+=, std::chrono::year_month_day::operator-=
From cppreference.com
< cpp | chrono | year month day
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.
[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 2020-07-01 #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
[edit] See also
(C++20) |
adds or subtracts a year_month_day and some number of years or months (function) |