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std::weak_ptr::expired

性病：弱[医]PTR：：过期

bool expired() const;​(since C++11)

检查托管对象是否已被删除。相当于use_count() == 0...

参数

%280%29

返回值

true如果托管对象已被删除，false否则。

例外

noexcept规格：

noexcept

注记

如果托管对象在线程之间共享，则此函数本质上是动态的。特别是，一个错误的结果可能在使用之前就会变得陈旧。真正的结果是可靠的。

例

演示如何使用过期来检查指针的有效性。

二次

#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(
}

二次

产出：

二次

gw is valid
gw is expired

二次

另见

lockcreates a shared_ptr that manages the referenced object (public member function)
use_countreturns the number of shared_ptr objects that manage the object (public member function)

 © cppreference.com

在CreativeCommonsAttribution下授权-ShareAlike未移植许可v3.0。

http：//en.cppreference.com/w/cpp/Memory/WILE[医]PTR/过期

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