# std::chrono::operator==,<=>(std::chrono::year_month)

< cpp‎ | chrono‎ | year month

定义于头文件 `<chrono>` |  |
constexpr bool operator==( const std::chrono::year_month& x, const std::chrono::year_month& y ) noexcept; | (1) | (C++20 起)
constexpr std::strong_ordering operator<=>( const std::chrono::year_month& x, const std::chrono::year_month& y ) noexcept; | (2) | (C++20 起)

比较二个 `year_month` 值 `x` 与 `y` 。

`<`、 `<=`、 `>`、 `>=` 及 `!=` 运算符分别从 `operator<=>` 与 `operator==` 合成。

### 返回值

1) x.year() == y.year() && x.month() == y.month()
2) x.year() <=> y.year() != 0 ? x.year() <=> y.year() : x.month() <=> y.month()

### 示例

    #include <iostream>
    #include <chrono>

    int main()
    {
        using namespace std::chrono;

        constexpr year_month ym1 {year(2021), month(7)};
        constexpr year_month ym2 {year(2021)/7};

        std::cout << std::boolalpha << (ym1 == ym2) << '\n';

        static_assert(
            (2020y/1 < 2020y/2) && (2020y/2 == 2020y/2) && (2020y/3 <= 2021y/3)
         && (2023y/1 > 2020y/2) && (3020y/2 != 2020y/2) && (2020y/3 >= 2020y/3)
        );
    }

输出：

    true