RTTI理解

几个例子，帮助理解 C++、C#、Java 中的运行时类型检查

RTTI（Run-Time Type Identification 运行时类型识别）允许用指向基类的指针或引用来操纵对象的程序能够获取到这些指针或引用所指对象的实际派生。

C++

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/**************************************************************************
	1. typeid      ：返回指针或引用所指对象的实际类型。
	2. dynamic_cast：将基类类型的指针或引用安全的转换为派生类型的指针或引用。
***************************************************************************/

#include <iostream>

using namespace std;

class Movable
{
public:
	Movable() { cout << "Movable constructed..." << endl; }
	virtual void move() = 0;
};

class Bus :public Movable
{
public:
	Bus() { cout << "Bus constructed..." << endl; }
	virtual void move() { cout << "Bus --> move" << endl; }
	void carry() { cout << "Bus --> carry" << endl; }
};

class Tank :public Movable
{
public:
	Tank() { cout << "Tank constructed..." << endl; }
	virtual void move() { cout << "Tank --> move" << endl; }
	void fire() { cout << "Tank --> fire" << endl; }
};

void CheckObjType(Movable &obj);
void CheckObjType(Movable *obj);

int main(int argc, char** argv)
{
	cout << "=====================    typeid    ====================" << endl;
	cout << "===================== dynamic_cast ====================" << endl;
	
	char a = 0;
	short b = 0;
	int c = 0;
	float d = 0;
	double e = 0;

	cout << "char   a --> typeid(a) == " << typeid(a).name() << endl
		 << "short  b --> typeid(b) == " << typeid(b).name() << endl
		 << "int    c --> typeid(c) == " << typeid(c).name() << endl
		 << "float  d --> typeid(d) == " << typeid(d).name() << endl
		 << "double e --> typeid(e) == " << typeid(e).name() << endl;

	Bus bus;
	Tank tank;

	CheckObjType(bus);
	CheckObjType(tank);

	cout << "=======================================================" << endl;
	CheckObjType(&bus);
	CheckObjType(&tank);
	
	return 0;
}

void CheckObjType(Movable &obj)
{
	obj.move();
	
	if (typeid(obj) == typeid(Bus))
	{
		Bus bus = dynamic_cast<Bus&>(obj);
		bus.carry();
	}
	else if (typeid(obj) == typeid(Tank))
	{
		Tank tank = dynamic_cast<Tank&>(obj);
		tank.fire();
	} 
	else
	{
		cout << "unknow type --> " << typeid(obj).name() << endl;
	}
}

void CheckObjType(Movable *obj)
{
	obj->move();

	if (typeid(*obj) == typeid(Bus))
	{
		Bus *pBus = dynamic_cast<Bus*>(obj);
		pBus->carry();
	}
	else if (typeid(*obj) == typeid(Tank))
	{
		Tank *pTank = dynamic_cast<Tank*>(obj);
		pTank->fire();
	}
	else
	{
		cout << "unknow type --> " << typeid(obj).name() << endl;
	}
}

C#

Java

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