C++ 强制类型转换

 1 #include <iostream>
 2 using namespace std;
 3 class A
 4 {
 5 public:
 6     operator int() { return 1; }
 7     operator char * (){ return NULL; }
 8 };
 9 int main()
10 {
11     A a;
12     int n; char * p = "New Dragon Inn";
13     n = static_cast<int>(3.14); // n 的值变为 3
14     n = static_cast<int>(a); //调用a.operator int, n的值变为 1
15     
16     p = static_cast<char*>(a); //调用a.operator char *,p的值变为 NULL
17     n = static_cast<int> (p); //编译错误， static_cast不能将指针转换成整型
18     p = static_cast<char*>(n); //编译错误， static_cast不能将整型转换成指针
19     return 0;
20 }

 1 #include <iostream>
 2 using namespace std;
 3 class A
 4 {
 5 public:
 6     int i;
 7     int j;
 8     A(int n):i(n),j(n) { }
 9 };
10 int main()
11 {
12     A a(100);
13     int & r = reinterpret_cast<int&>(a); //强行让 r 引用 a
14     r = 200; //把 a.i 变成了 200
15     cout << a.i << "," << a.j << endl; // 输出 200,100
16     int n = 300;
17     
18     A * pa = reinterpret_cast<A*> ( & n); //强行让 pa 指向 n
19     pa->i = 400; // n 变成 400
20     pa->j = 500; //此条语句不安全，很可能导致程序崩溃
21     cout << n << endl; // 输出 400
22     long long la = 0x12345678abcdLL;
23     pa = reinterpret_cast<A*>(la); // la太长，只取低32位0x5678abcd拷贝给pa
24     unsigned int u = reinterpret_cast<unsigned int>(pa); //pa逐个比特拷贝到u
25     cout << hex << u << endl; //输出 5678abcd
26     typedef void (* PF1) (int);
27     typedef int (* PF2) (int,char *);
28     PF1 pf1; PF2 pf2;
29     pf2 = reinterpret_cast<PF2>(pf1); //两个不同类型的函数指针之间可以互相转换
30 }
31 //输出结果
32 //200,100
33 //400
34 //5678abcd

 1 #include <iostream>
 2 #include <string>
 3 using namespace std;
 4 class Base
 5 { //有虚函数，因此是多态基类
 6 public:
 7     virtual ~Base() { }
 8 };
 9 class Derived:public Base { };
10 int main()
11 {
12     Base b;
13     Derived d;
14     Derived * pd;
15     pd = reinterpret_cast<Derived*> ( &b);
16     
17     if( pd == NULL) //此处pd不会为NULL。
18         //reinterpret_cast不检查安全性，总是进行转换
19         cout << "unsafe reinterpret_cast" << endl;
20     //不会执行
21     pd = dynamic_cast<Derived*> ( &b);
22     if( pd == NULL)
23         //结果会是NULL，因为 &b不是指向派生类对象，此转换不安全
24         cout << "unsafe dynamic_cast1" << endl; //会执行
25     Base * pb = & d;
26     pd = dynamic_cast<Derived*> ( pb); //安全的转换
27     if( pd == NULL) //此处pd 不会为NULL
28         cout << "unsafe dynamic_cast2" << endl; //不会执行
29     return 0;
30 }
31 //输出结果：
32 //unsafe dynamic_cast1