C++类型转换

static_cast（编译阶段）

• 用于类型相关的指针之间相互转换
• 用于基本类型的数据之间进行类型转换

#include <iostream>

class Base
{
public:
    int a;
};

class Derived : public Base
{
public:
    int b;
};

int main()
{
    Derived *p1 = new Derived();
    Base *p2 = static_cast<Base*>(p1);

    Base *p3 = new Base();
    Derived *p4 = static_cast<Derived*>(p3);

    int aa = 10;
    double bb = static_cast<double>(aa);

    double cc = 3.14f;
    int dd = static_cast<int>(cc);
}

dynamic_cast（运行阶段）

• 运行阶段执行类型检查

#include <iostream>

using namespace std;

class Fish
{
public:
    virtual void swim()
    {
        cout << "Fish swim in water" << endl;
    }

    virtual ~Fish()
    {}
};

class Tuna : public Fish
{
public:
    void swim()
    {
        cout << "tuna swims real fast in the sea" << endl;
    }
};

class Carp : public Fish
{
public:
    void swim()
    {
        cout << "carp swims real slow in the lake" << endl;
    }
};

void DetectFishType(Fish *fish)
{
    Tuna* p1 = dynamic_cast<Tuna *>(fish);
    if (p1)
        p1->swim();

    Carp* p2 = dynamic_cast<Carp *>(fish);
    if (p2)
        p2->swim();
}

int main()
{
    Tuna tuna;
    Carp carp;

    DetectFishType(&tuna);
    DetectFishType(&carp);
}

reinterpret_cast

• 能够让程序员能够将一种对象类型转换为另一种

---

应尽量避免在应用程序中使用reinterpret_cast，因为它让编译器将类型X视为不相关的类型Y，这看起来不像是优秀的设计或实现。

---

const_cast

• 让程序员能够关闭对象的访问修饰符const
  使用场景：拿到一个const引用的对象，通过这个对象操作非const的成员函数，编译器会报错，为了解决这个错误，需要使用到const_cast解除对象的const访问修饰符

#include <iostream>

using namespace std;

class A
{
public:
    void print()
    {
        cout << "A print" << endl;
    }
};

void printAllData(const A& a)
{
    A& ra = const_cast<A&>(a);

    ra.print();
}

int main()
{
    A a;

    printAllData(a);

    return 0;
}