shared_ptr، weak_ptr و گراف‌های مالکیت

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

struct Logger {
    std::string name;
    Logger(std::string n) : name(std::move(n)) {
        std::cout << name << " created\n";
    }
    ~Logger() { std::cout << name << " destroyed\n"; }
    void log(const std::string& msg) {
        std::cout << "[" << name << "] " << msg << '\n';
    }
};

int main() {
    auto logger = std::make_shared<Logger>("AppLogger");
    std::cout << "use_count: " << logger.use_count() << '\n';  // 1

    {
        auto copy = logger;  // shared ownership
        std::cout << "use_count: " << logger.use_count() << '\n';  // 2
        copy->log("inside scope");
    }  // copy destroyed, count drops to 1

    std::cout << "use_count: " << logger.use_count() << '\n';  // 1
    logger->log("still alive");
}  // logger destroyed — count drops to 0, Logger deleted

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

struct Employee;
struct Team {
    std::string name;
    std::vector<std::shared_ptr<Employee>> members;
    Team(std::string n) : name(std::move(n)) {}
    ~Team() { std::cout << "Team " << name << " destroyed\n"; }
};

struct Employee {
    std::string name;
    std::weak_ptr<Team> team;  // weak — does NOT own the team
    Employee(std::string n) : name(std::move(n)) {}
    ~Employee() { std::cout << "Employee " << name << " destroyed\n"; }

    void print_team() {
        if (auto t = team.lock()) {  // try to get shared_ptr
            std::cout << name << " belongs to " << t->name << '\n';
        } else {
            std::cout << name << " has no team\n";
        }
    }
};

int main() {
    auto team = std::make_shared<Team>("Engineering");
    auto alice = std::make_shared<Employee>("Alice");
    auto bob = std::make_shared<Employee>("Bob");

    team->members.push_back(alice);
    team->members.push_back(bob);
    alice->team = team;  // weak_ptr — no circular ownership
    bob->team = team;

    alice->print_team();  // "Alice belongs to Engineering"

    team.reset();  // destroy team
    alice->print_team();  // "Alice has no team" — weak_ptr expired
}

#include <memory>
#include <iostream>

struct Widget {
    int data[4];
};

int main() {
    // Two allocations: one for Widget, one for control block
    std::shared_ptr<Widget> p1(new Widget{});

    // Single allocation: Widget + control block together
    auto p2 = std::make_shared<Widget>();

    // Sizes (typical 64-bit platform)
    std::cout << "sizeof(Widget*):          " << sizeof(Widget*) << '\n';   // 8
    std::cout << "sizeof(unique_ptr<Widget>): " << sizeof(std::unique_ptr<Widget>) << '\n';  // 8
    std::cout << "sizeof(shared_ptr<Widget>): " << sizeof(std::shared_ptr<Widget>) << '\n';  // 16

    // shared_ptr is 2 pointers: one to object, one to control block
    // Control block contains: strong count, weak count, deleter, allocator

    std::cout << "p2 use_count: " << p2.use_count() << '\n';  // 1
    std::weak_ptr<Widget> w = p2;
    std::cout << "p2 use_count: " << p2.use_count() << '\n';  // still 1
    // weak_ptr does NOT increase strong count
}