How can I check if a weak pointer has expired before using it?

Question

Ryan McCombe · Accepted Answer

When working with weak pointers, it's important to check if the pointed-to object still exists before attempting to access it. You can do this using either the expired() method or by attempting to lock() the weak pointer:

Using expired():

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 (WeakPtr.expired()) {
9    std::cout << "WeakPtr has expired";
10  } else {
11    std::cout << "WeakPtr is valid. Value: "
12      << *WeakPtr.lock();
13  }
14}

1WeakPtr is valid. Value: 42

Using lock():

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 << "WeakPtr is valid. Value: "
10      << *LockedPtr;
11  } else {
12    std::cout << "WeakPtr has expired";
13  }
14}

1WeakPtr is valid. Value: 42

Both approaches allow you to safely handle cases where the weak pointer may have expired. Use expired() if you just need to check the status, and use lock() if you also need to access the pointed-to object if it exists.

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