Creating a Shared Pointer from a Weak Pointer

To access the object pointed to by a weak pointer, you need to create a shared pointer from it using the lock() method. This will return a shared_ptr that shares ownership of the object, if it still exists.

1#include <memory>
2#include <iostream>
3
4int main() {
5  auto SharedPtr{std::make_shared<int>(42)};
6  std::weak_ptr<int> WeakPtr{SharedPtr};
7
8  if (auto LockedPtr{WeakPtr.lock()}) {
9    std::cout << "Accessed value: " << *LockedPtr;
10  } else {
11    std::cout << "The object no longer exists";
12  }
13
14  SharedPtr.reset();
15
16  if (auto LockedPtr{WeakPtr.lock()}) {
17    std::cout << "\nAccessed value: "
18      << *LockedPtr;
19  } else {
20    std::cout << "\nThe object no longer exists";
21  }
22}

1Accessed value: 42
2The object no longer exists

It's crucial to check the returned shared_ptr before attempting to dereference it, as the original object may have been destroyed. If lock() returns an empty shared_ptr, dereferencing it will lead to undefined behavior.

By using lock(), you ensure that the object will remain alive at least as long as the shared_ptr created from the weak_ptr exists, preventing dangling pointers.