std::weak_ptr<T>::expired

 

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std::weak_ptr

成员函数

weak_ptr::weak_ptr

weak_ptr::~weak_ptr

weak_ptr::operator=

修改器

weak_ptr::reset

weak_ptr::swap

观察者

weak_ptr::use_count

weak_ptr::expired

weak_ptr::lock

weak_ptr::owner_before

weak_ptr::owner_hash (C++26)

weak_ptr::owner_equal (C++26)

非成员函数

swap(std::weak_ptr)

辅助类

atomic<std::weak_ptr> (C++20)

推导指南(C++17)

 

bool expired() const noexcept;		(自 C++11 起)

等效于 use_count() == 0。托管对象的析构函数可能尚未被调用，但此对象的析构即将发生（或可能已经发生）。

参数

(无)

返回值

如果托管对象已被删除，则为 true，否则为 false。

备注

如果托管对象在多个线程之间共享，则只有在 expired() 返回 true 时才有意义。

示例

演示如何使用 expired 检查指针的有效性。

运行此代码

#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();
}

输出

gw is valid
gw is expired

另请参阅

lock	创建一个管理引用对象的 shared_ptr (公共成员函数)
use_count	返回管理该对象的 shared_ptr 对象的数量 (公共成员函数)