std::weak_ptr::lock

From cppreference.com


std::shared_ptr<T> lock() const		(since C++11)

Creates a new shared_ptr that shares ownership of the managed object. If there is no managed object, i.e. *this is empty, then the returned shared_ptr also is empty.

Effectively returns expired() ? shared_ptr<T>() : shared_ptr<T>(*this).

Both this function and the constructor of shared_ptr may be used to acquire temporary ownership of the managed object. The difference is that the constructor of std::shared_ptr<T> throws an exception when the std::weak_ptr argument is empty, while std::weak_ptr<T>::lock() constructs an empty std::shared_ptr<T>.

[edit] Example

run this code

#include <iostream>
#include <memory>
#include <thread>
 
typedef std::shared_ptr<int> IntPtr;
typedef std::weak_ptr<int> IntWeakPtr;
 
void observe(IntWeakPtr pWeak) 
{
    IntPtr pObserve(pWeak.lock());
    if (pObserve) {
        std::cout << "\tobserve() able to lock weak_ptr<>, value=" << *pObserve << "\n";
    } else {
        std::cout << "\tobserve() unable to lock weak_ptr<>\n";
    }
}
 
int main()
{
    IntWeakPtr pWeak;
    std::cout << "weak_ptr<> not yet initialized\n";
    observe(pWeak);
 
    {
        IntPtr pShared(new int(42));
        pWeak = pShared;
        std::cout << "weak_ptr<> initialized with shared_ptr.\n";
        observe(pWeak);
    }
 
    std::cout << "shared_ptr<> has been destructed due to scope exit.\n";
    observe(pWeak);
}

Output:

weak_ptr<> not yet initialized
        observe() unable to lock weak_ptr<>
weak_ptr<> initialized with shared_ptr.
        observe() able to lock weak_ptr<>, value=42
shared_ptr<> has been destructed due to scope exit.
        observe() unable to lock weak_ptr<>

[edit] See also


expired	checks whether the referenced object was already deleted (public member function)

Language
Standard library headers
Concepts
Utilities library
Strings library
Containers library
Algorithms library
Iterators library
Numerics library
Input/output library
Localizations library
Regular expressions library (C++11)
Atomic operations library (C++11)
Thread support library (C++11)

std::weak_ptr::lock

Contents

[edit] Parameters

[edit] Return value

[edit] Exceptions

[edit] Notes

[edit] Example

[edit] See also