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title

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):

#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).

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