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# std::weak_ptr::lock

From cppreference.com
< cpp‎ | memory‎ | weak ptr

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).

### [edit] Parameters

(none)

### [edit] Return value

A `shared_ptr` which shares ownership of the owned object.

### [edit] Exceptions

`noexcept` specification:
noexcept

### [edit] Notes

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>

    void observe(std::weak_ptr<int> weak)
    {
        std::shared_ptr<int> observe(weak.lock());
        if (observe) {
            std::cout << "\tobserve() able to lock weak_ptr<>, value=" << *observe << "\n";
        } else {
            std::cout << "\tobserve() unable to lock weak_ptr<>\n";
        }
    }

    int main()
    {
        std::weak_ptr<int> weak;
        std::cout << "weak_ptr<> not yet initialized\n";
        observe(weak);

        {
            std::shared_ptr<int> shared(new int(42));
            weak = shared;
            std::cout << "weak_ptr<> initialized with shared_ptr.\n";
            observe(weak);
        }

        std::cout << "shared_ptr<> has been destructed due to scope exit.\n";
        observe(weak);
    }

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) [edit]

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