hour13_3.cpp

《24学时精通c++》的随书源码的下半部分。欢迎下载学习。

 // Listing 13.3
 // Copy constructors
 #include <iostream>
 
 class CAT
 {
 public:
     CAT();                         // default constructor
     CAT (const CAT &);     // copy constructor
     ~CAT();                         // destructor
     int GetAge() const { return *itsAge; }
     int GetWeight() const { return *itsWeight; }
     void SetAge(int age) { *itsAge = age; }
 
 private:
     int *itsAge;
     int *itsWeight;
 };
 
/* comment out our constructor and use the default
 CAT::CAT()
 {
     itsAge = new int;
     itsWeight = new int;
     *itsAge = 5;
     *itsWeight = 9;
 }
end of commented out constructor */

// Now the code won't behave like you expect (if it compiles) 
// because space is not allocated for itsAge or itsWeight to point to!
// When we try to change Age with SetAge, we may get a segmentation violation
// Since the pointer doesn't point anywhere correct.
 
 CAT::CAT(const CAT & rhs)
 {
     itsAge = new int;
     itsWeight = new int;
     *itsAge = rhs.GetAge();
     *itsWeight = rhs.GetWeight();
 }
 
 CAT::~CAT()
 {
     delete itsAge;
     itsAge = 0;
     delete itsWeight;
     itsWeight = 0;
 }
 
 int main()
 {
     CAT frisky;
     std::cout << "frisky's age: " << frisky.GetAge() << "\n";
     std::cout << "Setting frisky to 6...\n";
     frisky.SetAge(6);
     std::cout << "Creating boots from frisky\n";
     CAT boots(frisky);
     std::cout << "frisky's age: " << frisky.GetAge() << "\n";
     std::cout << "boots' age: " << boots.GetAge() << "\n";
     std::cout << "setting frisky to 7...\n";
     frisky.SetAge(7);
     std::cout << "frisky's age: " << frisky.GetAge() << "\n";
     std::cout << "boot's age: " << boots.GetAge() << "\n";
     return 0;
 }