2nd/10_Wiki/Topic_Programming/Topic_CPP/CPP_Virtual_Functions.md

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

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
cpp-virtual-functions	C++ Virtual Functions	Programming_Language	draft	conceptual		virtual keyword override keyword pointer type vs object type C++ 가상 함수		B	0.88	2026-07-04	2026-07-04			cpp programming-language w3schools oop virtual-functions polymorphism	https://www.w3schools.com/cpp/cpp_virtual_functions.asp

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++):

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).