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

# [[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):
```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).