Introduction to Weak Pointers

Smart pointer std::weak_ptr doesn't own the object it points to. This essentially means that a weak pointer doesn't increase the reference count of the object.

A std::weak_ptr allows access to an object managed by shared pointers without extending its lifetime. If all shared pointers go out of scope, the object is deleted, even if a weak pointer still exists. This is useful for observing shared objects without preventing their deallocation.

main.cpp


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#include <iostream>
#include <memory>

struct Resource {
    Resource() { std::cout << "Resource created\n"; }
    ~Resource() { std::cout << "Resource destroyed\n"; }
};

int main() 
{
    std::shared_ptr<Resource> sp1 = std::make_shared<Resource>();
    std::weak_ptr<Resource> wp = sp1; // Weak pointer does not increase ref count

    std::cout << "Shared pointer going out of scope...\n";
    sp1.reset(); // Resource is deleted

    if (wp.expired())
        std::cout << "Resource no longer exists\n";
}

The Lifecycle of a Weak Pointer

Weak pointers are observers they can access an object but don't extend its lifetime.

Their lifecycle depends on shared pointers. When the last shared pointer is destroyed, the object is deallocated, and the weak pointer expires. It still exists but becomes empty.

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Sezione 4. Capitolo 1

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Contenuti del Corso

C++ Smart Pointers

1. Introduction to Smart Pointers

Understanding Pointers Dynamic memory allocation The Need For Smart Pointers

2. Unique Pointers

Introduction to Unique Pointers Moving Unique Pointers Application For Unique Pointers Passing Around Unique Pointers Methods of a Unique Pointer

3. Shared Pointers

Introduction to Shared Pointers Creating and Sharing Shared Pointers Circular References and Shared Pointers

4. Weak Pointers

Introduction to Weak Pointers Creating And Using Weak Pointers Breaking Circular References With Weak Pointers Important Weak Pointer Functions

5. Advanced topics

Providing Custom Deleters For Smart Pointers Performance Considerations With Smart Pointers Overview Shared vs Unique vs Weak Pointers