RAII (Resource Acquisition Is Initialization)

RAII is the C++ idiom that ties the lifetime of a resource (memory, an open file, a held mutex, a network socket, a GPU handle) to the lifetime of an object. A constructor acquires the resource; the destructor releases it. When the object goes out of scope, the cleanup happens on its own, no matter how the scope exits. This chapter is the canonical introduction to the idiom: what it means, why it matters, what a hand-written RAII wrapper looks like, and when you absolutely need one.