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std::optional::has_value

可选：：操作符bool，std：：可选：：had[医]价值

constexpr explicit operator bool() const;​(since C++17)
constexpr bool has_value() const;​(since C++17)

检查是否*this包含一个值。

参数

%280%29

返回值

true如果*this包含一个值，false如果*this不包含值。

例外

noexcept规格：

noexcept

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