cpp_cast - ShenYj/ShenYj.github.io GitHub Wiki
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C语言风格的类型转换符
- (type)expression
- type(expression)
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C++中有4个类型转换符
- static_cast
- dynamic_cast
- reinterpret_cast
- const_cast
使用格式:xx_cast<type>(expression)
一般用于去除const属性,将const转换成非const
const Person *p1 = new Person();
p1->m_age = 10;
Person *p2 = const_cast<Person *>(p1);
p2->m_age = 20;
一般用于多态类型的转换,有运行时安全检测
class Person {
virtual void run() { }
};
class Student: public Person { };
class Car { };
int main() {
Person *p1 = new Person();
Person *p2 = new Student();
Student *stu1 = dynamic_cast<Student *>(p1); // NULL
Student *stu2 = dynamic_cast<Student *>(p2);
Car *car = dynamic_cast<Car *>(p1); // NULL
}
类似于强制转换
- 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
int a = 10;
const double d = static_cast<double>(a);
Person *p1 = new Person();
Person *p2 = new Student();
Student *stu1 = static_cast<Student *>(p1);
Student *stu2 = static_cast<Student *>(p2);
Car *car = static_cast<Car *>(p1);
- 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 *>(p1);
int *p = reinterpret_cast<int *>(100);
int *num = reinterpret_cast<int>(p);
int i = 10;
/// 不同类型之间转换可能会报错,所以类型改为引用类型, 但是最终d1的值实际并非10,多了四个字节的垃圾值
double d1 = reinterpret_cast<double &>(i);