C++ CoreLesson 08 of 441 min read6 questions

Static (outside classes)

File-scope static = internal linkage; static local = persists across calls.

Concept core idea Watch out easy to get wrong

Concept

Key concepts

static at file/global scope → internal linkage: symbol visible only in that translation unit (opposite of extern).
Two same-named non-static globals defined in two TUs → duplicate-symbol link error; bare extern int x; with no definition → 'undefined reference'.
static local variable → initialized once on first entry, retains value between calls, lifetime = whole program, scope = the function. Thread-safe init since C++11.
Global static init order across TUs is unspecified ('static initialization order fiasco'); static locals dodge it (init on first use).

Watch out

static (file) vs extern

static global = internal linkage (private to this file). extern = 'defined elsewhere, share it' (external linkage).

static local vs normal local

A normal local is created/destroyed each call. A static local is created once, keeps its value between calls, and lives for the whole program.

6 questions on this lesson. Write your answers from memory, then compare them with the model answers side by side.