THINK++ — Engineering Visualized

Lifetime & Linkage

Storage Classes

Storage classes define the scope, visibility, and lifetime of variables and functions in a C++ program.

auto

Default for local variables. Stored on stack.

static

Persists value between function calls. Allocated once.

extern

Refers to a global variable defined in another file.

register

Hint to store in CPU register (mostly ignored by modern compilers).

mutable

Allows modification of a member even in a const object.

THE STATIC KEYWORD

void counter() {
    static int c = 0; // initialized ONLY once
    cout << ++c << " ";
}
// Calling counter() 3 times prints: 1 2 3

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