C++标准转换运算符(3)

三、static_cast

static_cast的用途有3个：

1. 基本数据类型之间的相互转化；
2. 派生类指针或引用 和 基类指针或引用的相互转化。(dynamic_cast在把基类指针转化成派生类指针时，会编译错误；而static_cast不会提示编译错误，但是这种转化是不安全的。)
3. 各种指针类型 转换成 void *类型. (如果使用static_cast把void*类型转化为其它指针类型，编译器不会报错，但是转化行为不安全。)

class CBase {public: int bb;};
class CDerived: public CBase {public:int dd; };

int main(){ 
        CBase b; CBase* pb; CBase* pb2;
        b.bb = 50;
        CDerived d; CDerived* pd;
        d.bb =100;d.dd=200;
        void * p = NULL; 
        pb = static_cast<CBase*>(&d);    // ok: derived-to-base
        pd = static_cast<CDerived*>(&b); // base* ->derived *,  not safe 需要程序员保证指向完整的派生类对象
        
        p = static_cast<void*>(&d);  // other * -> void *, OK
        pb = static_cast<CBase*>(p);  // void * -> other *, not safe.
        pb2 = static_cast<CDerived*>(p);// void * -> other *, not safe.

        int dwA=10, *pB = NULL; 
        short int *pA=NULL, wB =20; 
//      pA = static_cast<short int *> (&dwA); // int * -> short * ,compile error.
//      pB = static_cast<int *> (&wB);    // short * -> int * ,compile error.
        
        p = static_cast<void *> (&wB);// other * -> void *, OK.
        pB = static_cast<int *> (p);// void * -> other *, not safe.
        uint64_t * pB2 = static_cast<uint64_t *> (p);// void * -> other *, not safe.

        wB = static_cast<short int> (dwA);// conversion between fundmental types, OK.
        dwA= static_cast<int>( wB);// conversion between fundmental types, OK.
        cout<<endl;
        return 0;
}