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title

C Storage Classes

🎯 한 줄 통찰 (One-line insight)

A static local variable inside a function survives BETWEEN separate calls to that function — the source's count() example prints 1, 2, 3 across three separate calls specifically because static makes the variable retain its value instead of resetting to 0 each time, whereas an ordinary local variable would print 1, 1, 1 — demonstrating that static fundamentally changes a variable's LIFETIME, not just its scope. [S1]

🧠 핵심 개념 (Core concepts)

Scope vs. storage class — scope defines WHERE a variable can be used; storage class defines HOW LONG it lasts and WHERE it's stored — two independent concepts. [S1]
auto — the default storage class for local variables inside functions; rarely written explicitly since it's already the default. [S1]
static — a local variable keeps its value across separate function calls (rather than resetting each call); a global variable/function marked static becomes invisible outside its own file. [S1]
register — suggests storing a variable in a CPU register for faster access; its address cannot be taken with &; considered mostly obsolete since modern compilers auto-optimize register allocation. [S1]
extern — tells the compiler a variable/function is DEFINED in another file, used for sharing variables across multiple source files. [S1]

📖 세부 내용 (Details)

static preserving value across calls: void count() { static int myNum = 0; myNum++; printf("num = %d\n", myNum); } int main() { count(); count(); count(); return 0; } — outputs num = 1, num = 2, num = 3 (removing static would reset to 1 each time). [S1]
extern sharing a variable across files: main.c declares extern int shared; while data.c defines int shared = 50;, compiled together via gcc main.c data.c -o program. [S1]

⚖️ 모순 및 업데이트 (Contradictions & updates)

static은 값을 유지, register는 사실상 구식: static이 함수 호출 간 값을 보존한다는 점과, register 키워드는 현대 컴파일러가 알아서 최적화하므로 명시적으로 쓸 필요가 거의 없다는 점이 함께 언급됨. [S1]

🛠️ 적용 사례 (Applied in summary)

현재 발견된 실제 적용 사례가 없습니다 — count() 함수가 호출될 때마다 값을 누적하는 static 카운터 패턴이 함수 호출 횟수를 추적하는 실전 활용의 대표 사례다. [S1]

💻 코드 패턴 (Code patterns)

A static local variable retaining its value across separate function calls (C):

void count() {
  static int myNum = 0; // Keeps its value between calls
  myNum++;
  printf("num = %d\n", myNum);
}
int main() {
  count(); // num = 1
  count(); // num = 2
  count(); // num = 3
  return 0;
}

✅ 검증 상태 및 신뢰도

상태: draft
검증 단계: conceptual
출처 신뢰도: B (W3Schools — widely used educational reference, not a primary standards body)
신뢰 점수: 0.86
중복 검사 결과: 신규 생성 (New discovery)

🔗 지식 그래프 (Knowledge Graph)

상위/루트: C Tutorial
관련 개념: C Constants, C Scope, C Fixed Width Ints
참조 맥락: 저장 클래스와 변수 생명주기 — 고정폭 정수(Fixed Width Ints) 챕터로 이어짐.

📚 출처 (Sources)

[S1] W3Schools — C Storage Classes — https://www.w3schools.com/c/c_storage_classes.php

📝 변경 이력 (Change history)

2026-07-04: Initial draft synthesized from the W3Schools "C Storage Classes" page (Astra wiki-curation, P-Reinforce v3.1 format).

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