What are the types of smart pointers in C++?

In C++, there are several main types of smart pointers that help manage object lifetimes and prevent memory leaks:

• std::unique_ptr — provides exclusive ownership of an object. The object is destroyed when the unique_ptr goes out of scope. It cannot be copied, but can be moved.

• std::shared_ptr — implements reference counting. Multiple pointers can own the same object, which is destroyed when the last shared_ptr is deleted.

• std::weak_ptr — a weak reference to an object managed by shared_ptr. It does not affect the object's lifetime and is used to prevent cyclic references.

Example usage:

#include <memory>
#include <iostream>

int main() {
    std::unique_ptr<int> p1 = std::make_unique<int>(42);
    // std::unique_ptr<int> p2 = p1; // Copy error
    std::unique_ptr<int> p2 = std::move(p1); // Move ownership

    std::shared_ptr<int> sp1 = std::make_shared<int>(100);
    std::shared_ptr<int> sp2 = sp1; // Reference count increases

    std::weak_ptr<int> wp = sp1; // Does not increase reference count

    std::cout << *sp2 << std::endl; // 100
}