RTTI(RunTime Type Information)执行时类型信息 具体解释

本文地址: http://blog.csdn.net/caroline_wendy/article/details/24369987

RTTI, RunTime Type Information, 执行时类型信息, 是多态的主要组成部分,

通过执行时(runtime)确定使用的类型, 执行不同的函数,复用(reuse)接口.

dynamic_cast<>能够 使基类指针转换为派生类的指针, 通过推断指针的类型, 能够决定使用的函数.

typeid(), 能够推断类型信息, 推断指针指向位置, 在多态中, 能够推断基类还是派生类.

代码:

/*

 * test.cpp

 *

 *  Created on: 2014.04.22

 *      Author: Spike

 */

/*eclipse cdt, gcc 4.8.1*/

#include <iostream>

#include <typeinfo>

using namespace std;

class Base {

public:

	virtual void fcnA() {

		std::cout << "base" << std::endl;

	}

};

class Derived : public Base {

public:

	virtual void fcnB() {

		std::cout << "derived" << std::endl;

	}

};

void fcnC(Base* p) {

	Derived* dp = dynamic_cast<Derived*>(p);

	if (dp != NULL)

		dp->fcnB();

	else

		p->fcnA();

}

void fcnD(Base* p) {

	if (typeid(*p) == typeid(Derived)) {

		Derived* dp = dynamic_cast<Derived*>(p);

		dp->fcnB();

	} else

		p->fcnA();

}

int main(void) {

	Base* cp = new Derived;

	std::cout << typeid(cp).name() << std::endl;

	std::cout << typeid(*cp).name() << std::endl;

	std::cout << typeid(&(*cp)).name() << std::endl;

	fcnC(cp);

	fcnD(cp);

	Base* dp = new Base;

	fcnC(dp);

	fcnD(dp);

	return 0;

}

输出:

P4Base

7Derived

P4Base

derived

derived

base

base

以上代码仅仅是演示样例,

详细使用时, 避免使用dynamic_cast<>和typeid()去推断类型, 直接通过多态就可以.

注意多态的绑定仅仅能通过指针, 如fcnC(Base*), 或引用, 如fcnD(Base&), 实现动态绑定,
两者效果同样;

都会依据输入的类型,动态绑定虚函数(virtual function).

代码例如以下:

/*

 * test.cpp

 *

 *  Created on: 2014.04.22

 *      Author: Spike

 */

/*eclipse cdt, gcc 4.8.1*/

#include <iostream>

#include <typeinfo>

using namespace std;

class Base {

public:

	virtual void fcn() {

		std::cout << "base" << std::endl;

	}

};

class Derived : public Base {

public:

	virtual void fcn() override {

		std::cout << "derived" << std::endl;

	}

};

void fcnC(Base* p) {

	p->fcn();

}

void fcnD(Base& p) {

	p.fcn();

}

int main(void) {

	Base* cp = new Derived;

	std::cout << typeid(cp).name() << std::endl;

	std::cout << typeid(*cp).name() << std::endl;

	fcnC(cp);

	fcnD(*cp);

	Base* dp = new Base;

	fcnC(dp);

	fcnD(*dp);

	Base& cr = *cp;

	std::cout << typeid(&cr).name() << std::endl;

	std::cout << typeid(cr).name() << std::endl;

	fcnC(&cr);

	fcnD(cr);

	Base& dr = *dp;

	fcnC(&dr);

	fcnD(dr);

	return 0;

}

输出:

P4Base

7Derived

derived

derived

base

base

P4Base

7Derived

derived

derived

base

base