Reset vs Release for Unique Pointers

The reset() and release() functions are both members of std::unique_ptr, but they serve different purposes in managing the ownership of the pointed-to object. Let's dive into each one:

The reset() Function

The reset() function does two things:

1. It deletes the currently owned object (if any).
2. It takes ownership of a new object (if provided).

Here's an example:

1#include <iostream>
2#include <memory>
3
4class Character {
5public:
6  std::string Name;
7};
8
9int main() {
10  auto Frodo{std::make_unique<Character>("Frodo")};
11  std::cout << "Before reset: " << Frodo->Name << '\n';
12
13  Frodo.reset(new Character("Samwise")); 
14  std::cout << "After reset: " << Frodo->Name << '\n';
15
16  Frodo.reset(); 
17  std::cout << "After reset to nullptr: "
18      << (Frodo ? Frodo->Name : "nullptr") << '\n';
19}

1Before reset: Frodo
2After reset: Samwise
3After reset to nullptr: nullptr

The release() Function

The release() function, on the other hand:

1. Releases ownership of the managed object without deleting it.
2. Returns a pointer to the managed object.
3. Sets the unique_ptr to null.

Here's an example:

1#include <iostream>
2#include <memory>
3
4class Character {
5public:
6  std::string Name;
7};
8
9int main() {
10  auto Gandalf{std::make_unique<Character>("Gandalf")};
11  std::cout << "Before release: " << Gandalf->Name << '\n';
12
13  Character* RawPtr{Gandalf.release()}; 
14  std::cout << "After release: "
15      << (Gandalf ? Gandalf->Name : "nullptr")
16      << '\n';
17  std::cout << "Raw pointer: " << RawPtr->Name << '\n';
18
19  delete RawPtr; // Don't forget to delete!
20}

1Before release: Gandalf
2After release: nullptr
3Raw pointer: Gandalf

Key Differences

Memory Management:

• reset() handles memory deallocation for you.
• release() leaves memory management to you.

Ownership:

• reset() can transfer ownership to the unique_ptr.
• release() transfers ownership away from the unique_ptr.

Return Value:

• reset() doesn't return anything.
• release() returns the raw pointer.

In general, reset() is safer and more commonly used, as it handles memory management automatically. Use release() with caution, typically when you need to transfer ownership to a different memory management scheme.