---
id: c-scope
title: "C Variable Scope"
category: "Programming_Language"
status: "draft"
verification_status: "conceptual"
canonical_id: ""
aliases: ["local scope", "global scope", "shadowing", "C 변수 스코프"]
duplicate_of: ""
source_trust_level: "B"
confidence_score: 0.86
created_at: 2026-07-04
updated_at: 2026-07-04
review_reason: ""
merge_history: []
tags: ["c", "programming-language", "w3schools", "scope"]
raw_sources: ["https://www.w3schools.com/c/c_scope.php"]
applied_in: []
github_commit: ""
---

# [[C Variable Scope]]

## 🎯 한 줄 통찰 (One-line insight)
When a local variable shares a name with a global variable, C doesn't merge or conflict them — it silently treats them as TWO COMPLETELY SEPARATE variables, and the source's own example proves it: the function prints its local `x` (22) while `main()` prints the untouched global `x` (5), meaning name collision between scopes causes no error at all, just quiet shadowing that can confuse anyone reading the code without realizing two different `x`s exist. [S1]

## 🧠 핵심 개념 (Core concepts)
- **Scope** — the region of code where a variable is accessible; in C, a variable is only usable within the region it was created. [S1]
- **Local scope** — a variable declared INSIDE a function belongs only to that function; using it outside causes a compile error. [S1]
- **Global scope** — a variable declared OUTSIDE any function is accessible from ANY scope, both other functions and `main()`. [S1]
- **Name collision = shadowing, not conflict** — a local variable with the SAME NAME as a global one creates two independent variables; inside the function, the LOCAL one takes precedence and the global remains untouched. [S1]
- **Global mutability risk** — because globals are reachable from anywhere, any function can silently modify one (e.g. `++x`), making the program's state harder to reason about. [S1]
- **Recommended practice** — prefer local variables for maintainability; understand globals because they appear often in existing/collaborative C code. [S1]

## 📖 세부 내용 (Details)
- Local variable inaccessible outside its function (produces an error): `void myFunction() { int x = 5; } int main() { myFunction(); printf("%d", x); /* error: x not accessible here */ }`. [S1]
- Global variable accessible everywhere: `int x = 5; void myFunction() { printf("%d", x); } int main() { myFunction(); printf("%d", x); }`. [S1]
- Same-name shadowing — two independent variables coexist: `int x = 5; void myFunction() { int x = 22; printf("%d\n", x); // 22, local } int main() { myFunction(); printf("%d\n", x); // 5, global — untouched }`. [S1]
- A function silently mutating a global: `int x = 5; void myFunction() { printf("%d\n", ++x); } int main() { myFunction(); printf("%d\n", x); } // x is now 6`. [S1]

## ⚖️ 모순 및 업데이트 (Contradictions & updates)
- **동일 이름의 지역/전역 변수는 충돌이 아니라 완전히 별개의 변수**: 함수 안의 지역 x(22)와 함수 밖의 전역 x(5)가 이름은 같지만 서로 독립적으로 존재하며, 함수 내부에서는 지역 변수가 우선한다는 점이 직접 예제로 증명됨. [S1]
- **전역 변수는 어디서든 수정 가능**: 어떤 함수든 전역 변수를 조용히 변경할 수 있으므로 주의해서 다뤄야 한다고 명시적으로 경고됨. [S1]

## 🛠️ 적용 사례 (Applied in summary)
현재 발견된 실제 적용 사례가 없습니다 — 기존 C 프로그램이나 협업 코드에서 전역 변수를 마주칠 가능성이 높으므로 스코프 동작 원리를 이해해두는 것이 실전에서 유용하다고 원문에 명시됨. [S1]

## 💻 코드 패턴 (Code patterns)
A local variable shadowing a global variable of the same name (C):
```c
int x = 5; // global
void myFunction() {
  int x = 22; // local, shadows the global
  printf("%d\n", x); // 22 (local x)
}
int main() {
  myFunction();
  printf("%d\n", x); // 5 (global x, untouched)
  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 Functions Inline]], [[C Storage Classes]], [[C User Input]]
- **참조 맥락:** 스코프 섹션 유일 챕터 — 사용자 입력(User Input) 챕터로 이어짐.

## 📚 출처 (Sources)
- [S1] W3Schools — C Variable Scope — https://www.w3schools.com/c/c_scope.php

## 📝 변경 이력 (Change history)
- 2026-07-04: Initial draft synthesized from the W3Schools "C Variable Scope" page (Astra wiki-curation, P-Reinforce v3.1 format).
