Try It Yourself - SyntaxStudy Editor

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#include <iostream>
#include <memory>
#include <string>
#include <vector>

struct Child;

struct Parent {
    std::string name;
    std::vector<std::shared_ptr<Child>> children;

explicit Parent(std::string n) : name(std::move(n)) {
        std::cout << "Parent '" << name << "' created
";
    }
    ~Parent() { std::cout << "Parent '" << name << "' destroyed
"; }
};

struct Child {
    std::string name;
    std::weak_ptr<Parent> parent;   // weak — no ownership cycle

explicit Child(std::string n) : name(std::move(n)) {
        std::cout << "Child '" << name << "' created
";
    }
    ~Child() { std::cout << "Child '" << name << "' destroyed
"; }

void greetParent() const {
        if (auto p = parent.lock()) {   // lock() returns shared_ptr or empty
            std::cout << name << " greets parent: " << p->name << "
";
        } else {
            std::cout << name << ": parent is gone
";
        }
    }
};

// enable_shared_from_this example
class Timer : public std::enable_shared_from_this<Timer> {
public:
    void scheduleCallback() {
        // Safe: captures a shared_ptr to self
        auto self = shared_from_this();
        std::cout << "Timer scheduled with use_count="
                  << self.use_count() << "
";
    }
};

int main() {
    auto parent = std::make_shared<Parent>("Alice");
    auto child  = std::make_shared<Child>("Bob");
    child->parent = parent;             // weak link — no cycle
    parent->children.push_back(child);

child->greetParent();

parent.reset();   // Parent destroyed (no cycle)
    child->greetParent();   // parent is gone

// enable_shared_from_this
    auto timer = std::make_shared<Timer>();
    timer->scheduleCallback();

return 0;
}