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

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