Smart Pointers

A smart pointer applies RAII to heap memory itself, so delete is called automatically — modern C++ code rarely calls new/delete directly at all.

#include <memory>

std::unique_ptr<int> owned = std::make_unique<int>(42);
std::cout << *owned << std::endl; // 42
// automatically deleted when owned goes out of scope

std::shared_ptr<int> shared1 = std::make_shared<int>(10);
std::shared_ptr<int> shared2 = shared1; // both now own it
std::cout << shared1.use_count() << std::endl; // 2
// deleted automatically once the LAST shared_ptr to it is gone

std::unique_ptr allows exactly one owner (it can be moved — see Move Semantics — but not copied); std::shared_ptr uses reference counting to allow multiple owners, at a small runtime cost for maintaining that count.

Common mistakes

• Reaching for std::shared_ptr by default — prefer std::unique_ptr unless shared ownership is a genuine requirement; it's cheaper and makes ownership unambiguous.
• Creating a reference cycle with two shared_ptrs pointing at each other — neither's count ever reaches zero, leaking both (fixed with std::weak_ptr for the back-reference, in real code).

Practice

Create a std::unique_ptr<std::string> holding "Hello" and print its contents.

std::unique_ptr<std::string> greeting = std::make_unique<std::string>("Hello");
std::cout << *greeting << std::endl;