C++: What are move semantics in C++?

1#include <utility>
2#include <iostream>
3
4class Buffer {
5private:
6    int* data;
7    size_t size;
8
9public:
10    // Constructor
11    Buffer(size_t s) : size(s) {
12        data = new int[s];
13        std::cout << "Constructed\n";
14    }
15
16    // Destructor
17    ~Buffer() {
18        delete[] data;
19        std::cout << "Destroyed\n";
20    }
21
22    // Copy constructor (expensive)
23    Buffer(const Buffer& other) : size(other.size) {
24        data = new int[size];
25        std::copy(other.data, other.data + size, data);
26        std::cout << "Copied\n";
27    }
28
29    // Move constructor (cheap!)
30    Buffer(Buffer&& other) noexcept : data(other.data), size(other.size) {
31        other.data = nullptr;  // Invalidate source
32        other.size = 0;
33        std::cout << "Moved\n";
34    }
35};
36
37int main() {
38    Buffer b1(100);      // Constructed
39    Buffer b2 = b1;      // Copied
40    Buffer b3 = std::move(b1);  // Moved!
41}  // b3 destroyed, b1 empty