ex2004.cpp

teach yourself C++ in 21 days 第五版

   // Exercise 20.4
   #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!!\n";
  }
        
  // 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;
  }
       
  // func. prototypes
  void MyFunction();
  unsigned int * FunctionTwo();
  void FunctionThree(unsigned int *);
        
  int main()
  {
     try
     {
        MyFunction();
     }
     // Only one catch required, use virtual functions to do the
     // right thing.
     catch (Exception& theException)
     {
        theException.PrintError();
     }
     return 0;
   }
  
  unsigned int * FunctionTwo()
  {
     unsigned int *myInt = new unsigned int;
    if (myInt == 0)
      throw OutOfMemory();
    return myInt;
  }
    
   void MyFunction()
   {
        unsigned int *myInt = FunctionTwo();
        FunctionThree(myInt);
        cout << "Ok. myInt: " << *myInt;
        delete myInt;
  }
    
  void FunctionThree(unsigned int *ptr)
  {
        long testNumber;
        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);
        *ptr = testNumber;
  }