C - Scope and Storage Classes

Scope determines where a name is visible. Storage class determines lifetime and linkage.

Learning Objectives

• Differentiate block, file, and global scope.
• Use static, extern, and automatic storage correctly.

Examples

#include <stdio.h>

int file_scope = 1;      // external linkage by default
static int internal = 2; // internal linkage (file-only)

void f(void) {
  static int counter = 0; // persists across calls
  int local = 5;          // automatic storage
  counter++;
  printf("%d %d %d\n", file_scope, internal, counter);
}

int main(void) {
  f(); f(); f();
}

Common Pitfalls

• Forgetting static when you want to preserve state across calls.
• Confusing static at file scope (internal linkage) vs inside a function (persistent lifetime).