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

观察器

weak_ptr::use_count

weak_ptr::expired

weak_ptr::lock

weak_ptr::owner_before

非成员函数

std::swap

辅助类

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

推导指引(C++17)

 

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

等价于 use_count() == 0 。可能仍未对被管理对象调用析构函数，但此对象的析构已经临近（或可能已发生）。

参数

（无）

返回值

若被管理对象已被删除则为 true ，否则为 false 。

注意

若被管理对象在线程间共享，则此函数内在地不可靠，通常 false 结果可能在能用之前就变得过时。 true 结果可靠。

示例

演示如何用 expired 检查指针的合法性。

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

参阅

lock	创建管理被引用的对象的shared_ptr (公开成员函数)
use_count	返回管理该对象的 shared_ptr 对象数量 (公开成员函数)