day17_类型转换

类型转换

• C语言风格的类型转换符
  • (type)expression
  • type(expression)
• C++中有4个类型转换符
  • static_cast
  • dynamic_cast
  • reinterpret_cast
  • const_cast

使用格式:xx_cast(expression)

const_cast

◼ 一般用于去除const属性，将const转换成非const

void test1const_cast() {
	const Person *p1 = new Person();

	Person *p2 = const_cast<Person *>(p1);
	Person *p3 = (Person *)p1;


	p2->m_age = 20;
	p3->m_age = 30;

	cout << p1->m_age << endl;
}

dynamic_cast

◼ 一般用于多态类型的转换，有运行时安全检测

void test2dynamic_cast() {
	Person *p1 = new Person();
	Person *p2 = new Student();

	/*Student *stu1 = (Student *) p1;
	Student *stu2 = (Student *) p2;
	Car *car = (Car *) p2;*/

	Student *stu1 = dynamic_cast<Student *>(p1);
	Student *stu2 = dynamic_cast<Student *>(p2);
	Car *car = dynamic_cast<Car *>(p2);

	cout << stu1 << endl;
	cout << stu2 << endl;
	cout << car << endl;
}

static_cast

◼ 对比dynamic_cast，缺乏运行时安全检测

◼ 不能交叉转换(不是同一继承体系的，无法转换)

◼ 常用于基本数据类型的转换、非const转成const

◼ 使用范围较广

void test3static_cast() {
	Person *p1 = new Person();
	Person *p2 = new Student();

	Student *stu1 = static_cast<Student *>(p1);
	Student *stu2 = static_cast<Student *>(p2);

	int i = 10;
	double d = i;

	cout << stu1 << endl;
	cout << stu2 << endl;
}

reinterpret_cast

◼ 属于比较底层的强制转换，没有任何类型检查和格式转换，仅仅是简单的二进制数据拷贝

◼ 可以交叉转换
◼ 可以将指针和整数互相转换

	Person *p1 = new Person();
	Person *p2 = new Student();

	Student *stu1 = reinterpret_cast<Student *>(p1);
	Student *stu2 = reinterpret_cast<Student *>(p2);
	Car *car = reinterpret_cast<Car *>(p2);

	cout << p1 << endl;
	cout << p2 << endl;
	cout << p2 << endl;

	cout << stu1 << endl;
	cout << stu2 << endl;
	cout << car << endl;