Weak Pointers with std::weak_ptr

Detecting Expired Weak Pointers

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

Illustration representing computer hardware

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.

This Question is from the Lesson:

Weak Pointers with `std::weak_ptr`

A full guide to weak pointers, using std::weak_ptr. Learn what they’re for, and how we can use them with practical examples

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This Question is from the Lesson:

Weak Pointers with `std::weak_ptr`

A full guide to weak pointers, using std::weak_ptr. Learn what they’re for, and how we can use them with practical examples

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Detecting Expired Weak Pointers

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

Weak Pointers with `std::weak_ptr`

How do I create a shared pointer from a weak pointer to access the pointed-to object?

Do weak pointers have any performance overhead compared to raw pointers?

Are weak pointers thread-safe? How can I use them safely in multithreaded code?

Can I store weak pointers in containers like `std::vector` or `std::map`?

Can I use custom deleters with weak pointers like I can with `unique_ptr` and `shared_ptr`?

Weak Pointers with `std::weak_ptr`

Professional C++

This course includes:

Professional C++

Detecting Expired Weak Pointers

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

Weak Pointers with std::weak_ptr

How do I create a shared pointer from a weak pointer to access the pointed-to object?

Do weak pointers have any performance overhead compared to raw pointers?

Are weak pointers thread-safe? How can I use them safely in multithreaded code?

Can I store weak pointers in containers like std::vector or std::map?

Can I use custom deleters with weak pointers like I can with unique_ptr and shared_ptr?

Weak Pointers with std::weak_ptr

Professional C++

This course includes:

Professional C++

Weak Pointers with `std::weak_ptr`

Can I store weak pointers in containers like `std::vector` or `std::map`?

Can I use custom deleters with weak pointers like I can with `unique_ptr` and `shared_ptr`?

Weak Pointers with `std::weak_ptr`