std::weak_ptr::expired

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C++
 
实用工具库
类型的支持 (basic types, RTTI, type traits)
动态内存管理
错误处理
程序实用工具
可变参数函数
日期和时间
函数对象
initializer_list（C++11）
bitset
hash（C++11）
关系运算符
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Relational operators
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rel_ops::operator!=
rel_ops::operator>
rel_ops::operator<=
rel_ops::operator>=
双和元组
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Pairs and tuples
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pair
tuple（C++11）
piecewise_construct_t（C++11）
piecewise_construct（C++11）
掉期，远期和移动
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Swap, forward and move
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swap
forward（C++11）
move（C++11）
move_if_noexcept（C++11）
declval（C++11）
 
动态内存管理
低级别的内存管理
分配器
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Allocators
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allocator
allocator_traits（C++11）
allocator_arg_t（C++11）
allocator_arg（C++11）
uses_allocator（C++11）
scoped_allocator_adaptor（C++11）
未初始化的存储空间
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Uninitialized storage
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uninitialized_copy
uninitialized_copy_n（C++11）
uninitialized_fill
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raw_storage_iterator
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智能指针
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Smart pointers
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unique_ptr（C++11）
shared_ptr（C++11）
weak_ptr（C++11）
auto_ptr（过时了）
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bad_weak_ptr（C++11）
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垃圾收集的支持
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Garbage collection support
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杂项
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Miscellaneous
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pointer_traits（C++11）
addressof（C++11）
align（C++11）
C库
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C Library
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std::weak_ptr
成员函数
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Member functions
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weak_ptr::weak_ptr
weak_ptr::~weak_ptr
weak_ptr::operator=
修饰符
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Modifiers
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weak_ptr::reset
weak_ptr::swap
观察员
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Observers
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weak_ptr::use_count
weak_ptr::expired
weak_ptr::lock
weak_ptr::owner_before
非成员函数
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Non-member functions
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std::swap
 
bool expired() const;
 （C++11 起）
检查是否被管理对象已经被删除。相当于use_count() == 0.
Original:
Checks whether the managed object has already been deleted. Equivalent to use_count() == 0.
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目录

[编辑] 参数

（无）
Original:
(none)
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[编辑] 返回值

true如果被管理对象已经被删除，false否则.
Original:
true if the managed object has already been deleted, false otherwise.
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[编辑] 例外

noexcept specification:  
noexcept
  （C++11 起）

[编辑] 注释

expired()可能会更快，比use_count().
Original:
expired() may be faster than use_count().
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[编辑] 为例

演示如何使用过期的检查有效性的指针.
Original:
Demonstrates how expired is used to check validity of the pointer.
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#include <iostream>
#include <memory>
 
std::weak_ptr<int> gw;
 
void f()
{
    if (!gw.expired()) {
	std::cout << "gw is valid\n";
    }
    else {
        std::cout << "gw is expired\n";
    }
}
 
int main()
{
    {
        auto sp = std::make_shared<int>(42);
	gw = sp;
 
	f();
    }
 
    f();
}

Output: 

gw is valid
gw is expired


[编辑] 另请参阅
创建一个shared_ptr管理引用的对象
Original:
creates a shared_ptr that manages the referenced object
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（公共成员函数） [edit]
返回shared_ptr对象，管理对象的数量
Original:
returns the number of shared_ptr objects that manage the object
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（公共成员函数） [edit]
来自“http://zh.cppreference.com/mwiki/index.php?title=cpp/memory/weak_ptr/expired&oldid=26702”