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+---
+id: c-macros
+title: "C Preprocessor and Macros"
+category: "Programming_Language"
+status: "draft"
+verification_status: "conceptual"
+canonical_id: ""
+aliases: ["#define", "#ifdef", "conditional compilation", "C 전처리기와 매크로"]
+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", "preprocessor", "macros"]
+raw_sources: ["https://www.w3schools.com/c/c_macros.php"]
+applied_in: []
+github_commit: ""
+---
+
+# [[C Preprocessor and Macros]]
+
+## 🎯 한 줄 통찰 (One-line insight)
+`#define PI 3.14` doesn't create a variable at all — the preprocessor performs a pure TEXT REPLACEMENT of every literal occurrence of `PI` with `3.14` BEFORE the compiler ever sees the code, meaning macros exist in an entirely different phase from variables/constants (which are compiled), which is also why parameterized macros like `SQUARE(x)` need careful parenthesization — they're substituting raw text, not evaluating an expression with real function-call semantics. [S1]
+
+## 🧠 핵심 개념 (Core concepts)
+- **Preprocessor** — runs BEFORE actual compilation; handles directives (lines starting with `#`) like including files and defining macros. [S1]
+- **`#include`** — angle brackets `< >` for standard libraries, double quotes `" "` for your own header files. [S1]
+- **`#define NAME value`** — creates a macro; every literal occurrence of `NAME` in the code is textually replaced with `value` before compilation. [S1]
+- **Parameterized macros** — `#define SQUARE(x) ((x) * (x))` behaves like a function shortcut, but is really TEXT SUBSTITUTION, so careful parenthesization is required to avoid operator-precedence mistakes. [S1]
+- **`#ifdef` / `#ifndef`** — conditional compilation; includes or skips code blocks depending on whether a macro is defined, useful for debug builds or program variants. [S1]
+
+## 📖 세부 내용 (Details)
+- Basic value macro: `#define PI 3.14 int main() { printf("Value of PI: %.2f\n", PI); return 0; }`. [S1]
+- Parameterized macro: `#define SQUARE(x) ((x) * (x)) printf("Square of 4: %d\n", SQUARE(4));`. [S1]
+- Conditional compilation gated on a defined macro: `#define DEBUG int main() { #ifdef DEBUG printf("Debug mode is ON\n"); #endif return 0; }` — if `DEBUG` were undefined, that block would be skipped entirely. [S1]
+
+## ⚖️ 모순 및 업데이트 (Contradictions & updates)
+- **매크로는 변수가 아니라 텍스트 치환**: #define PI 3.14는 컴파일 전에 코드상의 PI를 문자 그대로 3.14로 바꿔치기하는 전처리 단계 작업이며, 변수나 상수처럼 컴파일되는 개념이 아니라는 점이 확인됨. [S1]
+
+## 🛠️ 적용 사례 (Applied in summary)
+DEBUG 매크로가 정의되어 있을 때만 디버그 메시지를 출력하는 조건부 컴파일이 원문에서 직접 실전 활용 사례로 제시됨(디버깅이나 프로그램 버전 분기에 유용). [S1]
+
+## 💻 코드 패턴 (Code patterns)
+Conditional compilation — code included only if a macro is defined (C):
+```c
+#define DEBUG
+int main() {
+  #ifdef DEBUG
+  printf("Debug mode is ON\n");
+  #endif
+  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 Type Conversion]], [[C Organize Code]], [[C Null]]
+- **참조 맥락:** 전처리기와 매크로 — NULL(Null) 챕터로 이어짐.
+
+## 📚 출처 (Sources)
+- [S1] W3Schools — C Preprocessor and Macros — https://www.w3schools.com/c/c_macros.php
+
+## 📝 변경 이력 (Change history)
+- 2026-07-04: Initial draft synthesized from the W3Schools "C Preprocessor and Macros" page (Astra wiki-curation, P-Reinforce v3.1 format).