一個用來展示 C++ casting 的簡單程序

  1 #include <iostream>
  2 using std::cout;
  3 using std::endl;
  4
  5 class base {
  6 public:
  7     int x;
  8
  9     base() { x = 0; };
 10     virtual ~base() {};
 11 };
 12
 13 class child_a : public base {
 14 public:
 15     int a;
 16
 17     child_a() { a = 0; };
 18 };
 19
 20 class child_b : public base {
 21 public:
 22     int b;
 23
 24     child_b() { b = 0; };
 25 };
 26
 27 void class_check_a(base *p) {
 28     child_a     *ptr_a;
 29
 30     // check actual object type
 31     ptr_a = dynamic_cast<child_a*>(p);
 32
 33     if(ptr_a) {
 34         cout << "It is a child a" << endl;
 35     } else {
 36         cout << "It is not a child a" << endl;
 37     }
 38 }
 39
 40 void class_check_b(base *p) {
 41     child_b     *ptr_b;
 42
 43     // check actual object type
 44     ptr_b = dynamic_cast<child_b*>(p);
 45
 46     if(ptr_b) {
 47         cout << "It is a child b" << endl;
 48     } else {
 49         cout << "It is not a child b" << endl;
 50     }
 51 }
 52
 53 int main(int argc, char* argv[]) {
 54     // RTTI example
 55     child_a     a;
 56     child_b     b;
 57
 58     class_check_a(&a);
 59     class_check_a(&b);
 60
 61     class_check_b(&a);
 62     class_check_b(&b);
 63
 64     // reinterpret_cast and static_cast
 65     int     num_base = 10;
 66     double  num_1 = 0, num_2 = 0;
 67
 68     num_1 = static_cast<double>(num_base);
 69     //num_2 = reinterpret_cast<double&>(num_base);
 70
 71     cout << "num_base = " << num_base << endl;
 72     cout << "num_1 = " << num_1 << endl;
 73     cout << "num_2 = " << num_2 << endl;
 74
 75     // const_cast
 76     const child_a   ca;
 77     child_a         *ptr_ma;
 78
 79     cout << "ca.a = " << ca.a << endl;
 80    
 81     // enable it to generate error message
 82     // becasue ca is a constant class
 83     //ca.a = 10;
 84
 85     // from const to non-const
 86     ptr_ma = const_cast<child_a*>(&ca);
 87     ptr_ma->a = 10;
 88
 89     cout << "ca.a = " << ca.a << endl;
 90    
 91     return 0;
 92 }
 93
 94