int *n= new int;
double *d=reinterpret_cast<double*> (n);

int n=9;
double d=static_cast<double>(n);

int n=9;
double d=reinterpret_cast<double & >(n);

 1 #include <iostream>
 2 using std::cout;
 3 using std::endl;
 4 class CBaseX
 5 {
 6     public:
 7         int x;
 8         CBaseX() { x = 10; }
 9         void foo() { printf("CBaseX::foo() x=%d/n", x); }
10 };
11 class CBaseY
12 {
13     public:
14         int y;
15         int* py;
16         CBaseY() { y = 20; py = &y; }
17         void bar() { printf("CBaseY::bar() y=%d, *py=%d/n", y, *py);}
18 };
19 class CDerived : public CBaseX, public CBaseY
20 {
21     public:
22         int z;
23 };
24
25 int main(int argc, char *argv[])
26 {
27     float f = 12.3;
28     float* pf = &f;
29
30     //基本类型的转换
31     cout<<"=================Basic Cast================="<<endl;
32     //======static cast<>的使用:
33     int n = static_cast<int>(f); //成功编译
34     cout<<"n is :"<<n<<endl;//n = 12
35     //int* pn = static_cast<int*>(pf);//编译错误，指向的类型是无关的,不能将指针指向无关的类型
36     void* pv = static_cast<void*>(pf);//编译成功
37     int* pn2 = static_cast<int*>(pv);//成功编译, 但是 *pn2是无意义的内存（rubbish）
38     cout<<"pf is:"<<pf<<",pv is:"<<pv<<",pn2 is:"<<pn2<<endl;//三者值一样
39     cout<<"*pf is:"<<*pf<<",*pn2 is:"<<*pn2<<endl;//pf=12.3,pn2是无用值，注意无法使用"*pv"因为编译错。
40
41     //======reinterpret_cast<>的使用:
42     //int i = reinterpret_cast<int>(f);//编译错误，类型‘float’到类型‘int’的转换无效.
43     //成功编译, 但是 *pn 实际上是无意义的内存,和 *pn2一样
44     int* pi = reinterpret_cast<int*>(pf);
45     cout<<"pf is:"<<pf<<",pi is:"<<pi<<endl;//值一样
46     cout<<"*pf is:"<<*pf<<",*pi is:"<<*pi<<endl;//pi是无用值，和pn2一样。
47
48
49     //对象类型的转换
50     cout<<"=================Class Cast================="<<endl;
51     CBaseX cx;
52     CBaseY cy;
53     CDerived cd;
54
55     CDerived* pD = &cd;
56     CBaseX *pX = &cx;
57     CBaseY *pY = &cy;
58     cout<<"CDerived* pD = "<<pD<<endl;
59
60     //======static_cast<>的使用:
61     CBaseY* pY1 = pD;  //隐式static_cast转换
62     //不一样是因为多继承，pD还要前移动以便也指向CBaseX.
63     cout<<"CDerived* pD = "<<pD<<",CBaseY* pY1 = "<<pY1<<endl;//pY1=pD+4!!!!!!
64
65     //CDerived* pD1 = pY1;//编译错误,类型 ‘CBaseY*’ 到类型 ‘CDerived*’ 的转换无效
66     CDerived* pD1 = static_cast<CDerived*>(pY1);//成功编译
67     cout<<"CDerived* pD1 = "<<pD1<<endl;//现在 pD1 = pD
68
69     //pX = static_cast<CBaseX*>(pY);//编译错误，从类型 ‘CBaseY*’ 到类型 ‘CBaseX*’ 中的 static_cast 无效。
70     pD1 = static_cast<CDerived*>(pY);//竟然可以编译通过!!!!!!
71     cout<<"CDerived* pD1 = "<<pD1<<",CBaseY *pY = "<<pY<<endl;//现在 pD1 = pY-4
72     //======reinterpret_cast<>的使用:
73     CBaseY* pY2 = reinterpret_cast<CBaseY*>(pD);// 成功编译, 但是 pY2 不是 CBaseY*
74     cout<<"CDerived* pD = "<<pD<<",CBaseY* pY2 = "<<pY2<<endl;//pY2=pD!!!!!!
75
76     //======通过void的转换注意：
77     CBaseY* ppY = pD;
78     cout<<"CDerived* pD = "<<pD<<",CBaseY* ppY = "<<ppY<<endl;//ppY = pD + 4
79
80     void* ppV1 = ppY; //成功编译
81     cout<<"CBaseY* ppY = "<<ppY<<",void* ppV1 = "<<ppV1<<endl;//ppV1 = ppY
82
83     //CDerived* ppD2 = ppV1;//编译错误,类型‘void*’ 到类型 ‘CDerived*’的转换无效
84     CDerived* ppD2 = static_cast<CDerived*>(ppV1);
85     cout<<"CDerived* ppD2 = "<<ppD2<<endl;//ppD2 = ppY, 但是我们预期 ppD2 = ppY - 4 = pD
86     //ppD2->bar();//系统崩溃,段错误
87     return 0;
88 }

 1 #include <iostream>
 2 using std::cout;
 3 using std::endl;
 4
 5 class CTest
 6 {
 7     public:
 8         CTest(int i){m_val = i;cout<<"construction"<<m_val<<endl;}
 9         ~CTest(){cout<<"destructionn"<<endl;}
10         void SelfAdd(){m_val++;};
11         int m_val;
12 };
13
14 int main(int argc, char *argv[])
15 {
16     const int ic = 100;
17     //int cc = const_cast<int>(ic);//编译错误
18     int cc = const_cast<int&>(ic);
19     cout<<cc<<endl;//输出100
20     //const_cast<int &>(&ic)=200;//编译错误，从类型 ‘const int*’ 到类型 ‘int&’ 中的 const_cast 无效
21     const_cast<int &>(ic)=200;
22     cout<<ic<<endl;//输出100
23     cout<<*(&ic)<<endl;//输出100
24     //int *pc = &ic;//编译错误，从类型 ‘const int*’ 到类型 ‘int*’ 的转换无效
25     const int *pc=&ic;
26     //const_cast<int &>(pc)=200;//编译错误，从类型 ‘const int**’ 到类型 ‘int*’ 中的 const_cast 无效
27     const_cast<int &>(ic)=200;
28     //printf("%d,%d/n", ic, *pc);
29     cout<<ic<<','<<*pc<<endl;//100,200
30     //int *ppc = const_cast<int*>(ic);//编译错误
31     int *ppc = const_cast<int*>(&ic);
32     *ppc = 300;
33     cout<<ic<<','<<*ppc<<endl;//100,300
34
35     const CTest test(1000);
36     CTest test2(1050);
37     //test = test2;//编译错误，无法给常量赋值
38     const_cast<CTest &>(test)= test2;
39     cout<<test.m_val<<endl;//输出1050
40 }