Derived classes from base classes

• • Reply

  18 years ago

  by qwijibow

  Chris Stones

  England Nottingham, United Kingdom

  Joined 19 years ago

  Ok children, before i giveyou the problem id just like to explain what im trying to do.
  

  
  The 1 major difference between C++ and every other language ive learned, is the strings, you cant compare & or + them, also there are no built in functions to change there case (upper or lower) determine there length or to get a small section of them, (for searching).
  

  
  So, to learn how to use these strings i decided to make a string Class, which would have all these functions, as i thought it would be a good was to learn these new string rules.
  

  
  I have created my class, it has all the described functions, ( all work fine ) ( and the operators '=' {makes the string equal to  a sting on the right} '==' which compares 2 classes and returns true of false, and '&' which appends two string classes together.
  

  
  anouther problem, was the string length, unlike in VB it has to be fixed ( thee array has to be declaired with a constant).
  

  
  As this class i created was for my use whenever i wanted to use a clas,,, BIG or Small and wanting to be a 'GOOD' programmer didnt want to use massive strings in cases when i only needed to store a name, I thought i could use inheritance to solve my problem.
  

  
  As a variables in a derived class override the variables in the base class ( when names are identicle ) i thought i could derive MANY classes from the base class which used al of the same functions and variables but with 1 difference,,,, the member char array would be of different sizes,, ( i used protected, not private incase u thought i made that mistake)
  

  
  The only problem,,, The Over loaded operators dont seems to be inherited by the drived class Why the hell not ??
  

  
  

  
  I realise i may seem very dumb, but ive only been learning c++ for a couple of weeks, so forgive me for any obviouse mistakes or bad practices i am using.
  Here is my code for any1 who thinks they can point out whats wrong,
  

  
  ThanX
  

  
  (NOTE, if you try to use this in a c++ program, you will notice that if you use the base class CStrClass Everything works fine, but the classes derived from it do not.)
  

  
  

  
  

  
  // StrClass.h
  // Basic String Functions
  //-----------------------------------------------------------------------------------------------------------------------------
  // Base Class    | CStrClass     |                          |  Holds Strings of Max Length 1024  + Null
  // Derived Class | CStrClass64   |  Derived From CStrClass  |  Holds Strings of Max Length 64    + Null
  // Derived Class | CstrClass128  |  Derived From CStrClass  |  Holds Strings of Max Length 128   + Null
  // Derived Class | CstrClass256  |  Derived From CStrClass  |  Holds Strings of Max Length 256   + Null
  // Derived Class | CstrClass128  |  Derived From CStrClass  |  Holds Strings of Max Length 512   + Null
  // Derived Class | CstrClass128  |  Derived From CStrClass  |  Holds Strings of Max Length 2048  + Null
  // Derived Class | CstrClass128  |  Derived From CStrClass  |  Holds Strings of Max Length 5120  + Null
  // Derived Class | CstrClass128  |  Derived From CStrClass  |  Holds Strings of Max Length 10240 + Null
  //-----------------------------------------------------------------------------------------------------------------------------
  // Class Functions::      |   Returns:  |  Parameters:                    | Description:
  // UCase                  |   void      |  void                             | Converts all lowercase characters to uppercase.
  // LCase                  |   void      |  void                             | Converts all uppercase characters to lowercase.
  // GetChar                |   char      |  (int N)                          | Returns Nth Character of the member char array.
  // SetChar                |   void      |  (int N, char C)                  | Gets the Nth character to character C.
  // GetPointer             |   char*     |  void                             | Returns a pointer to the string, use to acces the string directly, Eg cout << MyString.GetPointer();
  // GelLen                 |   int       |  void                             | Returns the number of characters in the string (excluding the terminating NULL '\0')
  // Mid                    |   void      |  (char pchar, int start, int len) | Read (len) Number of Characters From the member char arrar starting from character (start). and put the characters in the character array which pchar points to,, eg. MyString.Mid( &AString[0], 2, 5) or, MyString.Mid( MyString.GetPointer(), 2, 5)
  //-----------------------------------------------------------------------------------------------------------------------------
  // OverLoaded Operators:  |  Returns:    |  Parameters: |    Description:
  //                      = |  void        |  char* pchar |    Copys the string pointer pchar points to into the member char array.
  //                      = |  void        |  Same Class  |    Copys the string from the parameter class into its own.
  //                     == |  bool        |  Same Class  |    Compares the parameter class' string with its own, returns true if the two are identicle.
  //                      & |  Same Class  |  Same Class  |    Appends the Parameters class' string to its own.
  //
  // *************************************************************************************************************************
  // Base Class
  class CStrClass
  {
  protected:
     char mcharString[1024];
     int  miMaxIndex;
     void mvChangeCase(bool Upper);        
  

  
  public:
     CStrClass()                  {miMaxIndex = 1024; mcharString[0] = '\0'; mcharString[miMaxIndex] = '\0';}
     void UCase()                 {mvChangeCase(true);}
     void LCase()                 {mvChangeCase(false);}
     char GetChar(int N)          {return mcharString[N];}
     void SetChar(int N, char C)  {mcharString[N] = C;}
     char* GetPointer()           {return &mcharString[0];}
     int  GetLen();
     void Mid(char* pchar,int start, int len);
     
     void       operator =   (char* pchar)
     {
         int N=0;
         while ((*(pchar + N) != '\0') && ( N < miMaxIndex ))
         {
             mcharString[N] = *(pchar + N);
             N++;
         }
         mcharString[N] = '\0';
     }
     void       operator =   (CStrClass TempClass);
     bool       operator ==  (CStrClass TempClass);
     CStrClass  operator &   (CStrClass TempClass);
  };
  // ****************************************
  // ****************************************
  // Derived Class'
  class CStrClass64: CStrClass
  {
  protected:
     char mcharString[64];
  public:
     CStrClass64(){miMaxIndex = 64; mcharString[0] = '\0'; mcharString[miMaxIndex] = '\0';}
  };
  //-----------------------------------------------------------------------------------------------------------------------------
  class CStrClass128: CStrClass
  {
  protected:
     char mcharString[128];
  public:
     CStrClass128(){miMaxIndex = 128; mcharString[0] = '\0'; mcharString[miMaxIndex] = '\0';}
  };
  //-----------------------------------------------------------------------------------------------------------------------------
  class CStrClass256: CStrClass
  {
  protected:
     char mcharString[256];
  public:
     CStrClass256(){miMaxIndex = 256; mcharString[0] = '\0'; mcharString[miMaxIndex] = '\0';}
  };
  //-----------------------------------------------------------------------------------------------------------------------------
  class CStrClass512: CStrClass
  {
  protected:
     char mcharString[512];
  public:
     CStrClass512(){miMaxIndex = 512; mcharString[0] = '\0'; mcharString[miMaxIndex] = '\0';}
  };
  //-----------------------------------------------------------------------------------------------------------------------------
  class CStrClass2048: CStrClass
  {
  protected:
     char mcharString[2048];
  public:
     CStrClass2048(){miMaxIndex = 2048; mcharString[0] = '\0'; mcharString[miMaxIndex] = '\0';}
  };
  //-----------------------------------------------------------------------------------------------------------------------------
  class CStrClass5120: CStrClass
  {
  protected:
     char mcharString[5120];
  public:
     CStrClass5120(){miMaxIndex = 5120; mcharString[0] = '\0'; mcharString[miMaxIndex] = '\0';}
  };
  //-----------------------------------------------------------------------------------------------------------------------------
  class CStrClass10240: CStrClass
  {
  protected:
     char mcharString[10240];
  public:
     CStrClass10240(){miMaxIndex = 10240; mcharString[0] = '\0'; mcharString[miMaxIndex] = '\0';}
  };
  // *************************************************************************************************************************
  // *************************************************************************************************************************
  // Member Functions
  void CStrClass::mvChangeCase(bool Upper)
  {
     int N=0;
  

  
     while (N < GetLen())
     {
         if (Upper = true)
         {
             if ((mcharString[N] > 96) && (mcharString[N] < 123)) { mcharString[N] = mcharString[N] - 32; }
         }
         else
         {
             if ((mcharString[N] > 64) && (mcharString[N] < 91 )) { mcharString[N] = mcharString[N] + 32; }
         }
         N++;
     }
  }
  //-----------------------------------------------------------------------------------------------------------------------------
  // Public Functions
  int CStrClass::GetLen()
  {
     int N=0;
     while ((N < miMaxIndex) && (mcharString[N] != '\0' )) {N++;}
     return N;
  }
  //-----------------------------------------------------------------------------------------------------------------------------
  void CStrClass::Mid(char* pchar, int start, int len)
  {
     for (int N=start; N < (start + len); N++)
     {
         (pchar+(N-start)) = m_charString[N];
     }
     (pchar+(N-start)) = '\0';
  }
  // ****************************************
  // OverLoaded Operators *********************************
  // void CStrClass:perator = (char* pchar)
  //{
  //    int N=0;
  //    while ((*(pchar + N) != '\0') && ( N < miMaxIndex ))
  //    {
  //        mcharString[N] = *(pchar + N);
  //        N++;
  //    }
  //    mcharString[N] = '\0';
  //}
  //-------------------------------------------------------------------------------------------------------------------------
  void CStrClass:perator = (CStrClass TempClass)
  {
     int N=0;
     while ((TempClass.GetChar(N) != '\0' ) && ( N < miMaxIndex ))
     {
         mcharString[N] = TempClass.GetChar(N);
         N++;
     }
     mcharString[N] = '\0';
  }
  //-------------------------------------------------------------------------------------------------------------------------
  bool CStrClass:perator == (CStrClass TempClass)
  {
     bool Equal = true;
     int N=0;
     if (GetLen() != TempClass.GetLen())
     {return false;}
     else
     {
         while (( N < GetLen()) && (Equal = true))
         {
             if (mcharString[N] != TempClass.GetChar(N)) { Equal = false ;}
             N++;
         }
     }
     return Equal;
  }
  //-----------------------------------------------------------------------------------------------------------------------------
  CStrClass CStrClass:perator & (CStrClass TempClass)
  {
     CStrClass ReturnClass;
     int       N=0,X=0;
     while ((GetChar(N) != '\0') && (N < miMaxIndex))
     {
         ReturnClass.SetChar( N, GetChar(N));
         N++;
     }
     while ((TempClass.GetChar(X) != '\0') && ( N < m_iMaxIndex ))
     {
         ReturnClass.SetChar(N, TempClass.GetChar(X));
         N++;
         X++;
     }
     ReturnClass.SetChar(N,'\0');
     return ReturnClass;
  }
  

  
  // **************
  

  
  

  
  

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• • Reply

  18 years ago

  by dirso

  Edilson

  Campinas, Brazil, Brazil

  Joined 19 years ago

  Hi,
  

  
  Try to define mcharString as a char pointer (char *mcharString), and allocate memory for it inside the constructor.
  

  
  Try this:
  // Base Class
  class CStrClass
  {
  protected:
    char *mcharString;
    int  miMaxIndex;
    void m_vChangeCase(bool Upper);        
  

  
  public:
    CStrClass(int iMaxLength = 1024)                  
   {
        miMaxIndex = iMaxLength ;
        mcharString = new char[miMaxIndex + 1];
        memset(mcharString, miMaxIndex + 1, 0)
   
    }
    ~CStrClass(){ delete mcharString; }
  

  
  /// ...
  };
   
  

  
  // and try this 1 to ur derived classes
  // Derived Class'
  class CStrClass64: CStrClass
  {
  public:
    CStrClass64():CStrClass(64 /* change to value to the max length of ur class /)
    {
      / nothing to do here, the base class do it for u */
    }
  };
  

  
  I hope it helps,
  

  
  Best Regards,
  Dirso
  

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