#include <iostream>
using namespace std;


class Person
{
public:
	int m_a;
};

class Student
{
public:
	int m_b;
};

int main()
{
	Person p;
	Student s;

	Person* p1 = &p;
	Student* s1 = &s;

	//Student *s3 = static_cast<Student*>(p1); //编译时就检测，不能转换
	Student *s2 = (Student*)(p1); //父类转子类，可以但是越界访问了，严重的会引起崩溃，因为父类没有子类的属性m_b
	s2->m_b = 2;

	return 0;
}

dynamic_cast

#include <iostream>
using namespace std;


class Person
{
public:
	virtual void SayHello()
	{
	}
	int m_a;
};

class Student
{
public:
	virtual void SayHello()
	{
	}
	int m_b;
};

int main()
{
	Person p;
	Student s;

	Person* p1 = &p;
	Student* s1 = &s;

	//编译是通过的，运行时检测是否真正转换成功
	//此时p1位父类指针，将父类指针转换为子类指针，这里得到的是nullptr，即转换不成功，避免了可能的崩溃
	//此外，dynamic_cast，还要要求，父类有虚函数，才行否则编译时就报错了。
	//也就是说，dynamic_cast用于运行时检测，指针之间是否转换成功，这样就安全了一点。
	Student *s2 = dynamic_cast<Student*>(p1); 
	if (s2 != nullptr)
	{
		cout << "succeed" << endl;
	}

	return 0;
}