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10_Wiki/Topic_Programming/Topic_CPP/CPP_Virtual_Functions.md

@@ -0,0 +1,81 @@
+---
+id: cpp-virtual-functions
+title: "C++ Virtual Functions"
+category: "Programming_Language"
+status: "draft"
+verification_status: "conceptual"
+canonical_id: ""
+aliases: ["virtual keyword", "override keyword", "pointer type vs object type", "C++ 가상 함수"]
+duplicate_of: ""
+source_trust_level: "B"
+confidence_score: 0.88
+created_at: 2026-07-04
+updated_at: 2026-07-04
+review_reason: ""
+merge_history: []
+tags: ["cpp", "programming-language", "w3schools", "oop", "virtual-functions", "polymorphism"]
+raw_sources: ["https://www.w3schools.com/cpp/cpp_virtual_functions.asp"]
+applied_in: []
+github_commit: ""
+---
+
+# [[CPP Virtual Functions]]
+
+## 🎯 한 줄 통찰 (One-line insight)
+Without the `virtual` keyword, a base-class pointer calls the function based on its DECLARED TYPE (`Animal*`), completely ignoring what it actually POINTS TO (a `Dog` object) — the source's own example proves this: `Animal* a = &d;` (where `d` is a `Dog`) still calls `Animal::sound()`, not `Dog::sound()`, UNTIL `virtual` is added to the base method, at which point the SAME pointer-based call correctly resolves to the actual object's type — meaning polymorphism through pointers doesn't work AT ALL by default in C++, and `virtual` is the specific opt-in required to make it happen. [S1]
+
+## 🧠 핵심 개념 (Core concepts)
+- **Virtual function** — a base-class member function that CAN be overridden in derived classes and resolved based on the ACTUAL object, not the pointer's declared type. [S1]
+- **Without `virtual`** — a base-class pointer always calls the BASE class's version of a method, even if it points to a derived-class object. [S1]
+- **With `virtual`** — the SAME pointer call now resolves to the DERIVED class's overridden version — this is how runtime polymorphism actually works in C++. [S1]
+- **`override` keyword** — optional but recommended in the derived class, for clarity (documents that this method is intentionally overriding a virtual base method). [S1]
+- **`->` operator** — accesses members through a pointer; shorthand for `(*pointer).member`. [S1]
+
+## 📖 세부 내용 (Details)
+- Without virtual — the base class's version runs despite the pointer pointing to a Dog: `class Animal { public: void sound() { cout << "Animal sound\n"; } }; class Dog : public Animal { public: void sound() { cout << "Dog barks\n"; } }; Animal* a; Dog d; a = &d; a->sound(); // "Animal sound" — WRONG, ignores actual object type`. [S1]
+- With virtual — the derived class's version correctly runs: `class Animal { public: virtual void sound() { cout << "Animal sound\n"; } }; class Dog : public Animal { public: void sound() override { cout << "Dog barks\n"; } }; Animal* a; Dog d; a = &d; a->sound(); // "Dog barks" — CORRECT`. [S1]
+- The `->` shorthand explained: `Animal* a = new Animal(); a->sound(); // same as (*a).sound();`. [S1]
+
+## ⚖️ 모순 및 업데이트 (Contradictions & updates)
+- **virtual 없이는 포인터 기반 다형성이 전혀 작동하지 않음**: Animal 포인터가 실제로는 Dog 객체를 가리키고 있어도 virtual이 없으면 항상 Animal::sound()가 호출된다는 점이 직접 예제로 증명됨 — virtual을 붙여야만 실제 객체 타입 기반으로 올바르게 해석됨. [S1]
+
+## 🛠️ 적용 사례 (Applied in summary)
+현재 발견된 실제 적용 사례가 없습니다 — 베이스 클래스 포인터로 파생 클래스 객체를 가리키고 올바른 오버라이드 메서드가 호출되도록 하는 것이 실전 다형성 구현의 핵심 요구사항이다. [S1]
+
+## 💻 코드 패턴 (Code patterns)
+virtual making a base-class pointer correctly resolve to the derived class's overridden method (C++):
+```cpp
+class Animal {
+public:
+  virtual void sound() { cout << "Animal sound\n"; }
+};
+class Dog : public Animal {
+public:
+  void sound() override { cout << "Dog barks\n"; }
+};
+int main() {
+  Animal* a;
+  Dog d;
+  a = &d;
+  a->sound(); // Outputs: Dog barks (correct, thanks to virtual)
+  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:** 0.88
+- **중복 검사 결과:** 신규 생성 (New discovery)
+
+## 🔗 지식 그래프 (Knowledge Graph)
+- **상위/루트:** [[C++ Tutorial]]
+- **관련 개념:** [[CPP Polymorphism]], [[CPP Pointers]], [[CPP Friend Function]]
+- **참조 맥락:** 가상 함수 — friend 함수(Friend Function) 챕터로 이어짐.
+
+## 📚 출처 (Sources)
+- [S1] W3Schools — C++ Virtual Functions — https://www.w3schools.com/cpp/cpp_virtual_functions.asp
+
+## 📝 변경 이력 (Change history)
+- 2026-07-04: Initial draft synthesized from the W3Schools "C++ Virtual Functions" page (Astra wiki-curation, P-Reinforce v3.1 format).