Move Constructor and Move Assignment Operator

Advanced14 min read•Updated: 2026-10-22

🏗️ Move Constructor and Move Assignment Operator

Introduction

While copy constructors duplicate dynamic memory buffers, move operations steal the existing pointer from the source object and set the source's pointer to nullptr. This turns an expensive O(N) memory allocation into a microsecond O(1) pointer swap.

💻 Full Custom Buffer Implementation

1#include <iostream>
2#include <utility>
3 
4class LargeDataBuffer {
5private:
6    int* m_data = nullptr;
7    std::size_t m_size = 0;
8 
9public:
10    // Parameterized Constructor
11    explicit LargeDataBuffer(std::size_t size)
12        : m_data(new int[size]{}), m_size(size) {
13        std::cout << "[ALLOC]: Allocated " << m_size << " integers on heap.\n";
14    }
15 
16    // Destructor
17    ~LargeDataBuffer() noexcept {
18        delete[] m_data;
19    }
20 
21    // 1. Move Constructor (Must be marked noexcept!)
22    LargeDataBuffer(LargeDataBuffer&& other) noexcept
23        : m_data(other.m_data), m_size(other.m_size) {
24        // Pilfer resources and nullify source:
25        other.m_data = nullptr;
26        other.m_size = 0;
27        std::cout << "[MOVE CONSTRUCTOR]: Transferred buffer ownership in O(1).\n";
28    }
29 
30    // 2. Move Assignment Operator
31    LargeDataBuffer& operator=(LargeDataBuffer&& other) noexcept {
32        if (this == &other) {
33            return *this; // Self-assignment guard
34        }
35 
36        // Clean up our current buffer
37        delete[] m_data;
38 
39        // Steal resources
40        m_data = other.m_data;
41        m_size = other.m_size;
42 
43        // Leave source in valid empty state
44        other.m_data = nullptr;
45        other.m_size = 0;
46 
47        std::cout << "[MOVE ASSIGNMENT]: Transferred buffer via operator= in O(1).\n";
48        return *this;
49    }
50 
51    std::size_t getSize() const noexcept { return m_size; }
52};
53 
54int main() {
55    LargeDataBuffer buf1(1000000); // 1 million integers on heap
56 
57    // Move constructor invoked:
58    LargeDataBuffer buf2 = std::move(buf1);
59 
60    LargeDataBuffer buf3(500);
61    // Move assignment operator invoked:
62    buf3 = std::move(buf2);
63 
64    std::cout << "Final buf3 size: " << buf3.getSize() << "\n";
65    return 0;
66}

⚡ Why `noexcept` is Mandatory for Move Operations

Standard containers like std::vector will refuse to move elements during reallocation and fall back to slow deep copying unless your move constructor is explicitly declared noexcept. This ensures the strong exception safety guarantee.

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Rvalue References (&&) and std::move Mechanics	The Rule of Five and Rule of Zero in Modern C++

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💻 Full Custom Buffer Implementation

1#include <iostream>
2#include <utility>
3 
4class LargeDataBuffer {
5private:
6    int* m_data = nullptr;
7    std::size_t m_size = 0;
8 
9public:
10    // Parameterized Constructor
11    explicit LargeDataBuffer(std::size_t size)
12        : m_data(new int[size]{}), m_size(size) {
13        std::cout << "[ALLOC]: Allocated " << m_size << " integers on heap.\n";
14    }
15 
16    // Destructor
17    ~LargeDataBuffer() noexcept {
18        delete[] m_data;
19    }
20 
21    // 1. Move Constructor (Must be marked noexcept!)
22    LargeDataBuffer(LargeDataBuffer&& other) noexcept
23        : m_data(other.m_data), m_size(other.m_size) {
24        // Pilfer resources and nullify source:
25        other.m_data = nullptr;
26        other.m_size = 0;
27        std::cout << "[MOVE CONSTRUCTOR]: Transferred buffer ownership in O(1).\n";
28    }
29 
30    // 2. Move Assignment Operator
31    LargeDataBuffer& operator=(LargeDataBuffer&& other) noexcept {
32        if (this == &other) {
33            return *this; // Self-assignment guard
34        }
35 
36        // Clean up our current buffer
37        delete[] m_data;
38 
39        // Steal resources
40        m_data = other.m_data;
41        m_size = other.m_size;
42 
43        // Leave source in valid empty state
44        other.m_data = nullptr;
45        other.m_size = 0;
46 
47        std::cout << "[MOVE ASSIGNMENT]: Transferred buffer via operator= in O(1).\n";
48        return *this;
49    }
50 
51    std::size_t getSize() const noexcept { return m_size; }
52};
53 
54int main() {
55    LargeDataBuffer buf1(1000000); // 1 million integers on heap
56 
57    // Move constructor invoked:
58    LargeDataBuffer buf2 = std::move(buf1);
59 
60    LargeDataBuffer buf3(500);
61    // Move assignment operator invoked:
62    buf3 = std::move(buf2);
63 
64    std::cout << "Final buf3 size: " << buf3.getSize() << "\n";
65    return 0;
66}

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Next Lesson

Rvalue References (&&) and std::move Mechanics

The Rule of Five and Rule of Zero in Modern C++

🏗️ Move Constructor and Move Assignment Operator

Introduction

💻 Full Custom Buffer Implementation

⚡ Why noexcept is Mandatory for Move Operations

The Rule of Five and Rule of Zero in Modern C++

Related Lessons

Practice Quiz

Loading Page Content...

🏗️ Move Constructor and Move Assignment Operator

Introduction

💻 Full Custom Buffer Implementation

⚡ Why noexcept is Mandatory for Move Operations

The Rule of Five and Rule of Zero in Modern C++

Related Lessons

Practice Quiz

⚡ Why `noexcept` is Mandatory for Move Operations

⚡ Why `noexcept` is Mandatory for Move Operations