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