C++: What is RAII and how do smart pointers implement it?

1// Manual RAII (pre-smart pointers)
2void risky() {
3    int* p = new int(10);
4    throw std::runtime_error("oops");  // Memory leak!
5    delete p;  // Never reached
6}
7
8// RAII with unique_ptr
9void safe() {
10    auto p = std::make_unique<int>(10);
11    throw std::runtime_error("oops");  // OK!
12    // p automatically deleted during stack unwinding
13}
14
15// Custom RAII wrapper
16template<typename T>
17class ScopedPtr {
18    T* ptr;
19public:
20    explicit ScopedPtr(T* p = nullptr) : ptr(p) {}
21    ~ScopedPtr() { delete ptr; }
22    T* operator->() { return ptr; }
23    T& operator*() { return *ptr; }
24    // Non-copyable
25    ScopedPtr(const ScopedPtr&) = delete;
26    ScopedPtr& operator=(const ScopedPtr&) = delete;
27    // Movable
28    ScopedPtr(ScopedPtr&& other) noexcept : ptr(other.ptr) {
29        other.ptr = nullptr;
30    }
31};