---
id: cpp-functions
title: "C++ Functions"
category: "Programming_Language"
status: "draft"
verification_status: "conceptual"
canonical_id: ""
aliases: ["void function", "function call", "declaration order matters", "C++ 함수"]
duplicate_of: ""
source_trust_level: "B"
confidence_score: 0.85
created_at: 2026-07-04
updated_at: 2026-07-04
review_reason: ""
merge_history: []
tags: ["cpp", "programming-language", "w3schools", "functions"]
raw_sources: ["https://www.w3schools.com/cpp/cpp_functions.asp"]
applied_in: []
github_commit: ""
---

# [[CPP Functions]]

## 🎯 한 줄 통찰 (One-line insight)
Calling a function BEFORE it's defined (with no prior declaration) is an explicit ERROR in C++ — the source shows `myFunction()` called inside `main()` at the top, with its full definition written BELOW, producing a compile error — a stricter behavior than what C-style top-down reading might suggest, meaning the declaration-above/definition-below organizational pattern isn't just a style preference here, it's the FIX for a real compile failure, not merely cosmetic. [S1]

## 🧠 핵심 개념 (Core concepts)
- **Function** — a block of code that only runs when CALLED. [S1]
- **`void` return type** — the function returns no value. [S1]
- **Calling before defining fails without a declaration** — if `myFunction()` is called in `main()` but only DEFINED below `main()` with no prior declaration, it's a compile error. [S1]
- **Declaration + definition split** — writing `void myFunction();` above `main()` and the full body below fixes the ordering problem while keeping code organized. [S1]

## 📖 세부 내용 (Details)
- The error case (calling before any declaration exists): `int main() { myFunction(); return 0; } void myFunction() { cout << "..."; } // Error`. [S1]
- The fix using forward declaration: `void myFunction(); int main() { myFunction(); return 0; } void myFunction() { cout << "I just got executed!"; }`. [S1]

## ⚖️ 모순 및 업데이트 (Contradictions & updates)
- **선언 없이 정의보다 먼저 호출하면 명시적 에러**: main() 안에서 함수를 호출하고 그 정의가 아래에 있을 뿐 사전 선언이 없으면 컴파일 에러가 발생한다는 점이 직접 예시로 확인됨 — C 챕터보다 이 문제를 더 명확히 강조함. [S1]

## 🛠️ 적용 사례 (Applied in summary)
현재 발견된 실제 적용 사례가 없습니다 — 함수 선언을 main() 위에 두고 정의를 아래에 두는 구조가 컴파일 에러를 피하면서 코드 가독성도 높이는 실전 표준 관행이다. [S1]

## 💻 코드 패턴 (Code patterns)
Forward-declaring a function above main() so it can be called before its full definition (C++):
```cpp
// Function declaration
void myFunction();

int main() {
  myFunction();  // works because of the forward declaration above
  return 0;
}

// Function definition
void myFunction() {
  cout << "I just got executed!";
}
```

## ✅ 검증 상태 및 신뢰도
- **상태:** draft
- **검증 단계:** conceptual
- **출처 신뢰도:** B (W3Schools — widely used educational reference, not a primary standards body)
- **신뢰 점수:** 0.85
- **중복 검사 결과:** 신규 생성 (New discovery)

## 🔗 지식 그래프 (Knowledge Graph)
- **상위/루트:** [[C++ Tutorial]]
- **관련 개념:** [[CPP Memory Management New]], [[CPP Function Param]], [[C Functions]]
- **참조 맥락:** 함수 섹션 첫 챕터 — 함수 매개변수(Function Param) 챕터로 이어짐.

## 📚 출처 (Sources)
- [S1] W3Schools — C++ Functions — https://www.w3schools.com/cpp/cpp_functions.asp

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