ex2003.cpp

teach yourself C++ in 21 days 第五版

  // Exercise 20.3
  #include <iostream>
  using namespace std;
  // Abstract exception data type
  class Exception 
  {
     public:
       Exception(){}
       virtual ~Exception(){}
       virtual void PrintError() = 0;
  };
 
  // Derived class to handle memory problems.
  // Note no allocation of memory in this class!
  class OutOfMemory : public Exception
  {
    public:
      OutOfMemory(){}
      ~OutOfMemory(){}
      virtual void PrintError();
    private:
  };
 
  void OutOfMemory::PrintError()
  {
     cout << "Out of Memory!!" << endl;
  }
 
  // Derived class to handle bad numbers
  class RangeError : public Exception
  {
    public:
      RangeError(unsigned long number){badNumber = number;}
      ~RangeError(){}
      virtual void PrintError();
      virtual unsigned long GetNumber() { return badNumber; }
      virtual void SetNumber(unsigned long number) {badNumber = number;}
    private:
      unsigned long badNumber;
  };
 
  void RangeError::PrintError()
  {
     cout << "Number out of range. You used " ;
     cout << GetNumber() << "!!" << endl;
  }
 
  void MyFunction();  // func. prototype
 
  int main()
  {
     try
     {
        MyFunction();
     }
     // Only one catch required, use virtual functions to do the
     // right thing.
     catch (Exception& theException)
     {
        theException.PrintError();
     }
     return 0;
  }
 
  void MyFunction()
  {
        unsigned int *myInt = new unsigned int;
        long testNumber;
   
        if (myInt == 0)
           throw OutOfMemory();
    
        cout << "Enter an int: ";
        cin >> testNumber;
   
        // this weird test should be replaced by a series
        // of tests to complain about bad user input
   
        if (testNumber > 3768 || testNumber < 0)
           throw RangeError(testNumber);
 
        *myInt = testNumber;
        cout << "Ok. myInt: " << *myInt;
        delete myInt;
  }