std::weak_ptr<T>::expired

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< cpp‎ | memory‎ | weak ptr
 
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std::weak_ptr
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weak_ptr::expired
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bool expired() const noexcept;
 (since 哋它亢++11)

Equivalent to use_count() == 0. The destructor for the managed object may not yet have been called, but this object's destruction is imminent (or may have already happened).

Parameters

(none)

Return value

true if the managed object has already been deleted, false otherwise.

Notes

This function is inherently racy if the managed object is shared among threads. In particular, a false result may become stale before it can be used. A true result is reliable.

Example

Demonstrates how expired is used to check validity of the pointer.

Run this code
#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

See also

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