# std::chrono::year::is_leap

< cpp‎ | chrono‎ | year

constexpr bool is_leap() const noexcept; |  | (C++20 起)

确定 *this 是否表示外推格里高利历中的闰年。

若存储的年份值满足下列条件则 *this 表示闰年

- 被 4 整除且不被 100 整除；或
- 被 400 整除。

### 返回值

若 `*this` 表示闰年则为 true ，否则为 false 。

### 示例

    #include <iostream>
    #include <chrono>

    int main()
    {
        using namespace std::chrono_literals;
        for (const std::chrono::year y : {2020y, 2021y, 2000y, 3000y}) {
            if (const int iy{ static_cast<int>(y) }; y.is_leap()) {
                std::cout << iy << " is a leap year because it is divisible by "
                          << (iy % 400 == 0 ? "400\n" : "4 and not divisible by 100\n");
            } else {
                std::cout << iy << " is not a leap year\n";
            }
        }
    }

输出：

    2020 is a leap year because it is divisible by 4 and not divisible by 100
    2021 is not a leap year
    2000 is a leap year because it is divisible by 400
    3000 is not a leap year