2nd/10_Wiki/Dev/Topic_C/C_Functions_Callback.md

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id	title	category	status	verification_status	canonical_id	aliases	duplicate_of	source_trust_level	confidence_score	created_at	updated_at	review_reason	merge_history	tags	raw_sources	applied_in	github_commit
c-functions-callback	C Callback Functions	Programming_Language	draft	conceptual		callback pattern qsort callback C 콜백 함수		B	0.87	2026-07-04	2026-07-04			c programming-language w3schools functions callbacks qsort	https://www.w3schools.com/c/c_functions_callback.php

C Callback Functions

🎯 한 줄 통찰 (One-line insight)

qsort() — a real C standard library function, not a toy example — proves that callbacks aren't merely a teaching device but the actual mechanism the STANDARD LIBRARY itself relies on: qsort() has no idea how to compare YOUR specific data, so it delegates that decision entirely to a compare() function you supply, meaning the library's generic sorting algorithm and your data-specific comparison logic stay completely decoupled. [S1]

🧠 핵심 개념 (Core concepts)

• Callback function — a function passed AS AN ARGUMENT to another function, which then calls it back whenever needed; implemented in C via function pointers. [S1]
• Decoupling logic from control flow — the RECEIVING function (runCallback, calculate, greet) doesn't need to know the callback's name in advance; it just needs a matching function-pointer type. [S1]
• Parameter-matching requirement — a callback with parameters requires the function pointer TYPE in the receiving function's signature to match exactly (void (*callback)(int, int)). [S1]
• Real standard-library usage: qsort() — from <stdlib.h>; you supply a compare() function, and qsort() calls it internally as many times as needed while sorting. [S1]

📖 세부 내용 (Details)

• Basic callback with before/after wrapping: void runCallback(void (*callback)()) { printf("Before calling the callback...\n"); callback(); printf("After calling the callback.\n"); } runCallback(sayHello);. [S1]
• Callback with parameters: void calculate(void (*callback)(int, int), int x, int y) { callback(x, y); } calculate(addNumbers, 5, 3);. [S1]
• Real-world qsort() usage with a user-supplied comparator: int compare(const void *a, const void *b) { return (*(int*)a - *(int*)b); } qsort(numbers, size, sizeof(int), compare);. [S1]

⚖️ 모순 및 업데이트 (Contradictions & updates)

• 현재까지 발견된 모순 사항 없음 (No contradictions found in available sources).

🛠️ 적용 사례 (Applied in summary)

표준 라이브러리의 qsort() 함수가 사용자 정의 compare() 콜백을 받아 정렬 기준을 위임받는 것이 콜백 패턴의 실제 실전 활용 사례로 원문에 직접 제시됨. [S1]

💻 코드 패턴 (Code patterns)

Using a user-supplied comparison callback with the standard library's qsort() (C):

#include <stdlib.h>
int compare(const void *a, const void *b) {
  return (*(int*)a - *(int*)b);
}
int main() {
  int numbers[] = { 5, 2, 9, 1, 7 };
  int size = sizeof(numbers) / sizeof(numbers[0]);
  qsort(numbers, size, sizeof(int), compare);
  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: 0.87
• 중복 검사 결과: 신규 생성 (New discovery)

🔗 지식 그래프 (Knowledge Graph)

• 상위/루트: C Tutorial
• 관련 개념: C Functions Pointers, C Functions Inline, C Scope
• 참조 맥락: 콜백 함수 — 인라인 함수(Functions Inline) 챕터로 이어짐.

📚 출처 (Sources)

• [S1] W3Schools — C Callback Functions — https://www.w3schools.com/c/c_functions_callback.php

📝 변경 이력 (Change history)

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