std::owner_less
Defined in header <memory> | | |
|---|---|---|
| (1) | |
template< class T > struct owner_less; /* undefined */ | (since C++11) (until C++17) | |
template< class T = void > struct owner_less; /* undefined */ | (since C++17) | |
template< class T > struct owner_less<std::shared_ptr<T>>; | (2) | (since C++11) |
template< class T > struct owner_less<std::weak_ptr<T>>; | (3) | (since C++11) |
template<> struct owner_less<void>; | (4) | (since C++17) |
此函数对象提供基于所有者的%28 AS，而不是两者的基于值的%29混合类型排序。std::weak_ptr和std::shared_ptr.顺序是这样的，只有当两个智能指针都是空的，或者它们都管理同一个对象时，它们才能比较等价的值，即使get()是不同的。因为它们指向同一对象%29内的不同子对象。
类模板是构建关联容器时的首选比较谓词。std::shared_ptr或std::weak_ptr作为钥匙，也就是说，
std::map<std::shared_ptr<T>, U,std::owner_less<std::shared_ptr<T>>>
或者。
std::map<std::weak_ptr<T>, U,std::owner_less<std::weak_ptr<T>>>...
默认operator<不是为弱指针定义的，并且可能错误地考虑了同一个对象的两个共享指针---非等效的%28(请参见shared_ptr::owner_before29%。
专门性
The standard library provides a specialization of std::owner_less when T is not specified. In this case, the parameter types are deduced from the arguments (each of which must still be either a std::shared_ptr or a std::weak_ptr). owner_less<void> function object providing mixed-type owner-based ordering of shared and weak pointers, regardless of the type of the pointee (class template specialization) | owner_less<void> | function object providing mixed-type owner-based ordering of shared and weak pointers, regardless of the type of the pointee (class template specialization) | (since C++17) |
|---|---|---|---|
owner_less<void> | function object providing mixed-type owner-based ordering of shared and weak pointers, regardless of the type of the pointee (class template specialization) |
成员类型
Member type | Definition |
|---|---|
result_type(deprecated in c++17) | 2-3) bool |
first_argument_type(deprecated in c++17) | 2) std::shared_ptr<T>3) std::weak_ptr<T> |
second_argument_type(deprecated in c++17) | 2) std::shared_ptr<T>3) std::weak_ptr<T> |
成员函数
operator() | compares its arguments using owner-based semantics (function) |
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STD：业主[医]减：：操作员%28%29
bool operator()( const std::shared_ptr<T>& lhs, const std::shared_ptr<T>& rhs ) const; | | (since C++11) (member only of owner_less<shared_ptr<T>> template specialization) |
|---|---|---|
bool operator()( const std::shared_ptr<T>& lhs, const std::weak_ptr<T>& rhs ) const; | | (since C++11) |
bool operator()( const std::weak_ptr<T>& lhs, const std::shared_ptr<T>& rhs ) const; | | (since C++11) |
bool operator()( const std::weak_ptr<T>& lhs, const std::weak_ptr<T>& rhs ) const; | | (since C++11) (member only of owner_less<weak_ptr<T>> template specialization) |
比较lhs和rhs使用基于所有者的语义。有效呼叫lhs.owner_before(rhs)...
排序是严格弱序关系。
lhs和rhs只有当它们都是空的或共享的所有权时，它们才是等价的。
参数
lhs, rhs | - | shared-ownership pointers to compare |
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返回值
true如果lhs是少于rhs由业主依据订单确定。
例外
(none) | (until C++17) |
|---|---|
noexcept specification: noexcept | (since C++17) |
另见
owner_before | provides owner-based ordering of shared pointers (public member function of std::shared_ptr) |
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owner_before | provides owner-based ordering of weak pointers (public member function of std::weak_ptr) |
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