operators (std::optional)
Defined in header <optional> | | |
|---|---|---|
Compare two optional objects | | |
template< class T, class U > constexpr bool operator==( const optional<T>& lhs, const optional<U>& rhs ); | (1) | (since C++17) |
template< class T, class U > constexpr bool operator!=( const optional<T>& lhs, const optional<U>& rhs ); | (2) | (since C++17) |
template< class T, class U > constexpr bool operator<( const optional<T>& lhs, const optional<U>& rhs ); | (3) | (since C++17) |
template< class T, class U > constexpr bool operator<=( const optional<T>& lhs, const optional<U>& rhs ); | (4) | (since C++17) |
template< class T, class U > constexpr bool operator>( const optional<T>& lhs, const optional<U>& rhs ); | (5) | (since C++17) |
template< class T, class U > constexpr bool operator>=( const optional<T>& lhs, const optional<U>& rhs ); | (6) | (since C++17) |
Compare an optional object with a nullopt | | |
template< class T > constexpr bool operator==( const optional<T>& opt, std::nullopt_t ); | (7) | (since C++17) |
template< class T > constexpr bool operator==( std::nullopt_t, const optional<T>& opt ); | (8) | (since C++17) |
template< class T > constexpr bool operator!=( const optional<T>& opt, std::nullopt_t ); | (9) | (since C++17) |
template< class T > constexpr bool operator!=( std::nullopt_t, const optional<T>& opt ); | (10) | (since C++17) |
template< class T > constexpr bool operator<( const optional<T>& opt, std::nullopt_t ); | (11) | (since C++17) |
template< class T > constexpr bool operator<( std::nullopt_t, const optional<T>& opt ); | (12) | (since C++17) |
template< class T > constexpr bool operator<=( const optional<T>& opt, std::nullopt_t ); | (13) | (since C++17) |
template< class T > constexpr bool operator<=( std::nullopt_t, const optional<T>& opt); | (14) | (since C++17) |
template< class T > constexpr bool operator>( const optional<T>& opt, std::nullopt_t ); | (15) | (since C++17) |
template< class T > constexpr bool operator>( std::nullopt_t, const optional<T>& opt ); | (16) | (since C++17) |
template< class T > constexpr bool operator>=( const optional<T>& opt, std::nullopt_t ); | (17) | (since C++17) |
template< class T > constexpr bool operator>=( std::nullopt_t, const optional<T>& opt ); | (18) | (since C++17) |
Compare an optional object with a T | | |
template< class T, class U > constexpr bool operator==( const optional<T>& opt, const U& value); | (19) | (since C++17) |
template< class T, class U > constexpr bool operator==( const U& value, const optional<T>& opt ); | (20) | (since C++17) |
template< class T, class U > constexpr bool operator!=( const optional<T>& opt, const U& value ); | (21) | (since C++17) |
template< class T, class U > constexpr bool operator!=( const U& value, const optional<T>& opt ); | (22) | (since C++17) |
template< class T, class U > constexpr bool operator<( const optional<T>& opt, const U& value ); | (23) | (since C++17) |
template< class T, class U > constexpr bool operator<( const U& value, const optional<T>& opt ); | (24) | (since C++17) |
template< class T, class U > constexpr bool operator<=( const optional<T>& opt, const U& value ); | (25) | (since C++17) |
template< class T, class U > constexpr bool operator<=( const U& value, const optional<T>& opt); | (26) | (since C++17) |
template< class T, class U > constexpr bool operator>( const optional<T>& opt, const U& value ); | (27) | (since C++17) |
template< class T, class U > constexpr bool operator>( const U& value, const optional<T>& opt ); | (28) | (since C++17) |
template< class T, class U > constexpr bool operator>=( const optional<T>& opt, const U& value ); | (29) | (since C++17) |
template< class T, class U > constexpr bool operator>=( const U& value, const optional<T>& opt ); | (30) | (since C++17) |
对optional物品。
1-6%29比较两optional物体，lhs和rhs使用相应的运算符将所包含的值%28进行比较。T%29只有当两者兼而有之时lhs和rhs包含值。否则，
lhs被认为等于rhs当且仅当lhs和rhs不包含值。
lhs被认为少于rhs如果，而且只有在这样的情况下，rhs包含一个值和lhs不会的。
7-18%29比较opt带着nullopt值等于%281-6%29。optional它不包含值。
19-30%29比较opt带着value。使用相应的运算符将值%28进行比较。T%29只在以下情况下opt包含一个值。否则，opt被认为少于value。如果对应的比较表达式*opt和value格式不正确，或者如果其结果不能转换为bool，该行为是未定义的。
参数
lhs, rhs, opt | - | an optional object to compare |
|---|---|---|
value | - | value to compare to the contained value |
返回值
1%29bool(lhs) != bool(rhs)、回报false
否则，如果bool(lhs) == false%28左右bool(rhs) == false以及%29，返回true
否则，返回*lhs == *rhs...
2%29bool(lhs) != bool(rhs)、回报true
否则，如果bool(lhs) == false%28左右bool(rhs) == false以及%29，返回false
否则，返回*lhs != *rhs...
3%29bool(rhs) == false回报false
否则，如果bool(lhs) == false、回报true
否则返回*lhs < *rhs...
4%29bool(lhs) == false回报true
否则，如果bool(rhs) == false、回报false
否则返回*lhs <= *rhs...
5%29bool(lhs) == false回报false
否则，如果bool(rhs) == false、回报true
否则返回*lhs > *rhs...
6%29bool(rhs) == false回报true
否则，如果bool(lhs) == false、回报false
否则返回*lhs >= *rhs...
7-8%29!opt...
9-10%29bool(opt)...
11%29false...
12%29bool(opt)...
13%29!opt...
14%29true...
15%29bool(opt)...
16%29false...
17%29true...
18%29!opt...
19%29bool(opt) ? *opt == value : false...
20%29bool(opt) ? value == *opt : false...
21%29bool(opt) ? *opt != value : true...
22%29bool(opt) ? value != *opt : true...
23%29bool(opt) ? *opt < value : true...
24%29bool(opt) ? value < *opt : false...
25%29bool(opt) ? *opt <= value : true...
26%29bool(opt) ? value <= *opt : false...
27%29bool(opt) ? *opt > value : false...
28%29bool(opt) ? value > *opt : true...
29%29bool(opt) ? *opt >= value : false...
30%29bool(opt) ? value >= *opt : true...
例外
1-6%29%280%29
7-18%29
noexcept规格：
noexcept
19-30%29%280%29
© cppreference.com在CreativeCommonsAttribution下授权-ShareAlike未移植许可v3.0。
本文档系腾讯云开发者社区成员共同维护，如有问题请联系 cloudcommunity@tencent.com
