[C++] cast

개요

• static_cast
  • 명시적(explicit) 변환
• const_cast
  • 상수성 추가/제거
• as_const
  • C++17
  • const reference로 변환
• dynamic_cast
  • 런타임에 다형성을 만족하는 파생 클래스 사이에서의 up/down cast
• reinterpret_cast
  • 강제 형변환

예제

• 코드

   #include <cstdlib>
   #include <iostream>
   #include <string>
   #include <typeinfo>
   #include <utility>
      
   using namespace std;
      
   void func(string *s) {
   	*s += "1";
   	cout << "call func(string* s)" << endl;
   }
   void func(const string *s) { cout << "call func(const string* s)" << endl; }
      
   void func(string &s) {
   	s += "1";
   	cout << "call func(string& s)" << endl;
   }
   void func(const string &s) { cout << "call func(const string& s)" << endl; }
      
   class Base {
   	public:
   		virtual ~Base() {}
   };
   class Derived : public Base {
   	public:
   		virtual ~Derived() {}
      
   		void show() { cout << 1 << endl; }
   };
      
   class Test1 {};
   class Test2 {
   	public:
   		void show() { cout << 1 << endl; }
   };
      
   int main() {
   	int i = 1;
   	cout << typeid(static_cast<double>(i)).name() << endl;
      
   	const string s = "abc";
   	func(const_cast<string *>(&s));
   	cout << s << endl;
      
   	string ss = "abc";
   	func(const_cast<const string *>(&ss));
   	cout << ss << endl;
      
   	string sss = "abc";
   	func(as_const(sss));
   	cout << sss << endl;
   	func(sss);
   	cout << sss << endl;
      
   	Base *base = NULL;
   	Derived *derived = new Derived;
   	base = dynamic_cast<Base *>(derived);
   	derived = dynamic_cast<Derived *>(base);
   	derived->show();
   	delete derived;
   	base = NULL;
   	derived = NULL;
      
   	Test1 *t1 = NULL;
   	Test2 *t2 = new Test2;
   	t1 = reinterpret_cast<Test1 *>(t2);
   	t2 = reinterpret_cast<Test2 *>(t1);
   	t2->show();
   	delete t2;
   	t1 = NULL;
   	t2 = NULL;
      
   	return 0;
   }
  

• 실행 결과

   d
   call func(string* s)
   abc1
   call func(const string* s)
   abc
   call func(const string& s)
   abc
   call func(string& s)
   abc1
   1
   1