std::weak_ptr<T>::expired

 

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std::weak_ptr

Member functions

weak_ptr::weak_ptr

weak_ptr::~weak_ptr

weak_ptr::operator=

Modifiers

weak_ptr::reset

weak_ptr::swap

Observers

weak_ptr::use_count

weak_ptr::expired

weak_ptr::lock

weak_ptr::owner_before

Non-member functions

std::swap

Helper classes

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

Deduction guides(C++17)

 

bool expired() const noexcept;		(since C++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

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