PricingLoginStart free
C++ Academy · Lesson

Move Constructors and Move Assignment

Implement move constructors and move assignment operators correctly.

Lesson 4 of 413 steps

Move Constructors and Move Assignment is a free C++ Academy lesson on CoddyKit. This is lesson 4 of 4. Any 3 lessons of this learning path are free to read in full — after that, CoddyKit PRO unlocks every lesson, plus hands-on practice with a built-in code editor and a 24/7 AI tutor. It is part of the C++ Academy learning path, and your progress syncs across the web and the CoddyKit app. The C++ Academy course includes 4 lessons in total.

Two Special Members

The move constructor and move assignment operator let your class take ownership of another instance s resources without copying.

Signature

Both take an rvalue reference to the same type.

class String {
public:
    String(String&& other) noexcept;          // move ctor
    String& operator=(String&& other) noexcept; // move assign
};

Implementing a Move Constructor

Steal the source s resources and leave it in a valid empty state.

String(String&& other) noexcept
    : data_(other.data_), size_(other.size_) {
    other.data_ = nullptr;
    other.size_ = 0;
}

Implementing Move Assignment

Three steps: release current resources, steal the source s, leave the source empty.

String& operator=(String&& other) noexcept {
    if (this != &other) {
        delete[] data_;
        data_ = other.data_;
        size_ = other.size_;
        other.data_ = nullptr;
        other.size_ = 0;
    }
    return *this;
}

Why noexcept Matters

Mark move operations noexcept whenever possible. Standard containers like std::vector only use moves on resize if they are noexcept; otherwise they fall back to copies for exception safety.

The Rule of Five

If you write any of these five, think about all five:

  • Destructor
  • Copy constructor
  • Copy assignment
  • Move constructor
  • Move assignment

The Rule of Zero

Even better — write none of them. Store members as RAII types (vectors, strings, smart pointers). Compiler-generated defaults work correctly and efficiently.

class Widget {
    std::string name_;
    std::vector<int> data_;
    // No need for destructor, copy, or move — compiler does the right thing
};

When the Compiler Generates Moves

The compiler generates default move members only when:

  • No user-declared copy constructor, copy assignment, destructor, or move members
  • All members and bases are themselves movable

Defaulted and Deleted Moves

You can request or forbid the compiler-generated moves explicitly.

class Widget {
public:
    Widget(Widget&&) = default;
    Widget& operator=(Widget&&) = default;
    // or
    Widget(Widget&&) = delete;
};

After a Move

The moved-from object is in a valid but unspecified state. You can:

  • Destroy it
  • Assign a new value to it
  • Call any operation that has no precondition (size(), empty(), clear())

Use Cases

Move semantics speeds up:

  • Returning large objects (when RVO does not kick in)
  • Putting big objects into containers (push_back of rvalues)
  • Implementing your own resource-owning types

Quick Check

Why should move constructors and move assignment operators be marked noexcept?

Answer it in the interactive lesson

Recap

Move constructors and move assignment operators steal resources from a soon-to-die rvalue. Mark them noexcept for container speed. Follow the Rule of Five — or better, the Rule of Zero by composing standard RAII types.

Free to start

Learn C++ with an AI tutor — free

Write and run real code in your browser, get instant help from a 24/7 AI tutor, and pick up where you left off on the web or in the app.

Courses
51
Lessons
203
Start learning freeView the full course

Frequently Asked Questions

Is the “Move Constructors and Move Assignment” lesson free?

Yes — any 3 lessons of the C++ Academy learning path, including “Move Constructors and Move Assignment”, are free to read in full here on the web. After that, CoddyKit PRO unlocks every lesson, plus interactive practice with a built-in code editor and a 24/7 AI tutor. The C++ Academy course includes 4 lessons in total.

What will I learn in “Move Constructors and Move Assignment”?

Implement move constructors and move assignment operators correctly. You practise C++ Academy with hands-on code you run directly in the browser, and a 24/7 AI tutor answers your questions as you work through the lesson.

Do I need any experience to start C++ Academy?

No prior experience is required. C++ Academy on CoddyKit is structured for beginners through advanced learners, so you can start here or from the beginning and move at your own pace. This is lesson 4 of 4.

How long does the “Move Constructors and Move Assignment” lesson take?

Most CoddyKit lessons take about 5–10 minutes. Each one is bite-sized and interactive, so you make steady progress and pick up exactly where you left off across the web and the app.

Can I write and run code in this C++ Academy lesson?

Yes. Every C++ Academy lesson includes a built-in code editor, so you write and run real code right in your browser and get instant AI feedback — no local setup required.

All lessons in this course

  1. Lvalue vs Rvalue The Distinction
  2. Rvalue References and the && Syntax
  3. std::move and std::forward
  4. Move Constructors and Move Assignment
← Back to C++ Academy