读书笔记：const_cast，reinterpret_cast,static_cast,dynamic_cast

1、reinterpret_cast

Allows any pointer to be converted into any other pointer type. Also allows any integral type to be converted into any pointer type and vice versa.

样例

int _tmain(int argc, _TCHAR* argv[])
{

CCTest objTest;
CCBase *p =  (CCBase*)reinterpret_cast<void*>(&objTest);

p->SetNumber1(1);   //CCBase::SetNumber1

CCTest *p2 =  (CCTest*)reinterpret_cast<void*>(&objTest);
p2->SetNumber1(1);   //CCTest::SetNumber1

unsigned int val = reinterpret_cast<unsigned int>( &objTest );  //objTest的地址

return 0;
}

2、const_cast

Removes the const, volatile, and __unaligned attribute(s) from a class.

样例：

int _tmain(int argc, _TCHAR* argv[])
{
int a = 12;
const int& a1= a;
const_cast<int&>(a1) =21;  // a:21,移除const常量声明
a1 =12;                    //Error:“a1”: 不能给常量赋值
return 0;
}

样例

class CCTest {
public:
void SetNumber1(int val) const
{
const_cast<CCTest*>(this)->number = val; //ok

}
void SetNumber2(int val) const
{
number = val;              //error C3490: 由于正在通过常量对象访问“number”，因此无法对其进行修改
}
private:
int number;
};

3、dynamic_cast

可以进行两个方向转换，downcast,upcast, 也就是派生类指针转换成基类指针，也可以基类指针转换成派生类指针。如果基类指针指向的对象地址是派生类对象，那么转换指针非空，否者为NULL.

CShape *pShape1 = new CRectangle();
try
{
CRectangle* p = dynamic_cast<CRectangle*>(pShape1);
}
catch (std::bad_cast&)
{

}