std::unique_ptr

Learn exclusive ownership with std::unique_ptr.

std::unique_ptr

std::unique_ptr is a smart pointer that provides exclusive ownership of an object. When the owner goes out of scope the pointed object is automatically deleted. It is defined in <memory>.

Example: std::unique_ptr<int> p(new int(42)); creates an int object. You access the value with *p. When p goes out of scope the int is automatically deleted; no delete is needed. A unique_ptr cannot be copied but can be moved (with std::move). This guarantees there is exactly one owner.

Move semantics

A unique_ptr cannot be copied but can be moved. To transfer ownership to another unique_ptr you use std::move: auto p2 = std::move(p1);. After this p1 becomes empty (nullptr).

Moving means ownership is transferred; there is no copy. So there is always exactly one owner. Returning a unique_ptr from a function also moves: return p; transfers ownership to the caller. This is very useful in factory functions; the created object's ownership safely passes to the caller.

Exercise Create a unique_ptr and print

Create a std::unique_ptr<int> with new int(42). Access the value with *p and print it with std::cout. Remember #include <memory> is required.

Show example solution

#include <iostream>
#include <memory>

int main() {
    std::unique_ptr<int> p(new int(42));
    std::cout << *p;
    return 0;
}

Test yourself

What happens when a unique_ptr goes out of scope?
```
{
    std::unique_ptr<int> p(new int(42));
} // end of scope
```
- Nothing happens
- A memory leak occurs
- The program crashes
- The pointed object is automatically deleted
Show answer

The pointed object is automatically deleted — The unique_ptr destructor automatically deletes the object.

Declare a unique_ptr

std::____<int> p(new int(42));

Show answer

std::unique_ptr<int> p(new int(42));

Match each feature to its meaning

std::unique_ptr

Exclusive ownership
std::move(p1)

Transfer ownership
*p

Access value
scope end

Automatic deletion

Next lesson: std::shared_ptr

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