C++: What is the difference between std::unique_ptr and std::shared_ptr?

std::unique_ptr:

• Exclusive ownership
• Zero overhead (same as raw pointer)
• Cannot be copied, only moved
• Use for single-owner scenarios

1auto p1 = std::make_unique<int[]>(100);
2auto p2 = std::move(p1); // p1 is now null

std::shared_ptr:

• Shared ownership with reference counting
• Overhead for control block
• Can be copied
• Use for shared ownership

1auto p1 = std::make_shared<int>(42);
2auto p2 = p1; // ref count = 2
3// Destroyed when last shared_ptr dies

Weak pointer: Breaks cycles in shared ownership:

1std::weak_ptr<Node> weak = shared;
2if (auto locked = weak.lock()) { /* use */ }