91 C++对象模型探索。RTTI运行时类型识别回顾与存储位置介绍

news2024/11/16 19:34:17

一，RTTI 运行时类型识别，简单回顾

C++运行时类型识别RTTI，要求父类这种必须至少有一个虚函数，如果父类中没有虚函数，那么得到的RTTI就不准确；

RTTI就可以在执行期间查询一个多态指针，或者多态应用的信息了

RTTI的能力靠 typeid和dynamic_cast运算符来体现。

class Teacher25base {
public:
	void virtual func() {
		cout << "Teacher25base virtual func called" << endl;
	}
	virtual ~Teacher25base(){
		cout << "Teacher25base virtual 析构函数被调用" << endl;
	}
};

class Teacher25son :public Teacher25base{

public:
	void virtual func() {
		cout << "Teacher25son virtual func called" << endl;
	}

	virtual ~Teacher25son() {
		cout << "Teacher25son virtual 析构函数被调用" << endl;
	}
};

void main() {
	Teacher25base *ptea = new Teacher25son;
	ptea->func();
	cout << "------" << endl;
	cout << typeid(ptea).name() << endl;//class Teacher25base *
	cout<<typeid(*ptea).name() << endl; //class Teacher25son

	Teacher25base * aa = dynamic_cast<Teacher25base *>(ptea);
	if (aa!=NULL) {
		cout << "aa == success" << endl; //ok
		aa->func();//注意这里：Teacher25son virtual func called
	}
	else {
		cout << "fail" << endl;
	}

	Teacher25son * bb = dynamic_cast<Teacher25son *>(ptea);
	if (bb != NULL) {
		cout << "bb = success" << endl;//ok
		bb->func(); //注意这里：Teacher25son virtual func called
	}
	else {
		cout << "fail" << endl;
	}
}

二 RTTI运行原理以及常用方法，以及RTTI的保存位置

typeid 返回的是一个常量对象的引用。

这个常量对象的类型一般是type_info（类）

class Teacher25base {
public:
	void virtual func() {
		cout << "Teacher25base virtual func called" << endl;
	}
	virtual ~Teacher25base(){
		cout << "Teacher25base virtual 析构函数被调用" << endl;
	}
};

class Teacher25son :public Teacher25base{

public:
	void virtual func() {
		cout << "Teacher25son virtual func called" << endl;
	}

	virtual ~Teacher25son() {
		cout << "Teacher25son virtual 析构函数被调用" << endl;
	}
};

void main() {
	Teacher25base *ptea = new Teacher25son;
	ptea->func();
	cout << "------" << endl;
	cout << typeid(ptea).name() << endl;//class Teacher25base *
	cout<<typeid(*ptea).name() << endl; //class Teacher25son

	Teacher25base * aa = dynamic_cast<Teacher25base *>(ptea);
	if (aa!=NULL) {
		cout << "aa == success" << endl; //ok
		aa->func();//注意这里：Teacher25son virtual func called
	}
	else {
		cout << "fail" << endl;
	}

	Teacher25son * bb = dynamic_cast<Teacher25son *>(ptea);
	if (bb != NULL) {
		cout << "bb = success" << endl;//ok
		bb->func(); //注意这里：Teacher25son virtual func called
	}
	else {
		cout << "fail" << endl;
	}

	const std::type_info &tp = typeid(*ptea);

	if (typeid(Teacher25son).name() == typeid(*ptea).name() )
	{
		cout << "相等" << endl;
	}
	else {
		cout << "bu相等" << endl;
	}
	//静态用法，不属于多态类型
	cout << typeid(int).name() << endl; // int
	cout << typeid(Teacher25base).name() << endl; //class Teacher25base
	cout << typeid(Teacher25base).raw_name() << endl;//.?AVTeacher25base@@
	cout << typeid(Teacher25base *).name() << endl;//class Teacher25base *
	cout << typeid(Teacher25base *).raw_name() << endl;//.PAVTeacher25base@@
	Teacher25base *ptea5 = new Teacher25base();
	cout << typeid(ptea5).name() << endl;//class Teacher25base *
	cout << typeid(*ptea5).raw_name() << endl;//.?AVTeacher25base@@

	cout << "断点在这里" << endl;

	//当我们把基类中的虚函数 都删除后，
	//测试如下的代码
	Teacher25base *ptea6 = new Teacher25son;
	cout << typeid(ptea6).name() << endl;//在基类没有虚函数的情况下，这块显示为 class Teacher25base
	//这说明：RTTI 一定和虚函数表有关系。如果没有虚函数表，RTTI就不准确。

	//没有虚函数的调用，没有父类子类的继承，就没有多态。

}