C++: What is std::unique_ptr and how does it work?

1#include <memory>
2
3class Resource {
4public:
5    Resource() { std::cout << "Acquired\n"; }
6    ~Resource() { std::cout << "Released\n"; }
7};
8
9// Create unique_ptr
10auto ptr = std::make_unique<Resource>();
11
12// Transfer ownership
13auto ptr2 = std::move(ptr);  // ptr is now nullptr
14
15// Release ownership
16Resource* raw = ptr2.release();
17delete raw;
18
19// Reset
20ptr2.reset(new Resource());
21
22// Custom deleter
23auto custom = std::unique_ptr<FILE, decltype(&fclose)>(
24    fopen("file.txt", "r"), &fclose
25);