Char array's in class's

• • Reply

  18 years ago

  by qwijibow

  Chris Stones

  England Nottingham, United Kingdom

  Joined 19 years ago

  hello children yep, i got anouther problem with C++
  

  
  ok, before any1 points this out to me, i am aware that there are header files that do what im trying to do, however im coding them myself in an attempt to learn the basics.
  

  
  I am trying to make a string class which replaces all those great VB string functions ,, eg Len() Mid() UCase() LCase() Right() Left().
  

  
  the problem is, that i have to declair a maximum length fro my string. to waste less memory, i have made a base class with all the functions that has the largest string [1024] and then i make loads of derived classes with only 1 difference,,,, the size of the string, so the user can use whatever class depending on wether they need to store a small name, or huge string.
  

  
  here's how it works..
  

  
  class CString1024
  {
  protected:
  char m_string[1024];
  

  
  public:
  //loads of functions and over loaded operators
  };
  

  
  class CString512: public String1024
  {
  protected:
  m_String[512]
  };
  

  
  

  
  

  
  as you can see, CString512 has a smaller string, but inherits all the fnctions from CString1024...
  and the idea was that it only used a string array of half the size,,
  

  
  BUT, testing has shown that all derived classes use the base class's size String.
  

  
  How do i fix this ?
  

  
  thanX
  

  
  

  
  

  
  

  
  

  
  

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• • Reply

  18 years ago

  by dirso

  Edilson

  Campinas, Brazil, Brazil

  Joined 19 years ago

  I think is better for u to declare as char pointer and allocate memory in the constructor. But if u don't wanna, try to use the <this> pointer. something like:
  

  
  char *String1024::Left(int n = 1)
  {
     char *resp = new char[n +1]
     memset(resp, 0, n+1);
     strcpy(resp, this->m_string, n);
     return resp;
  }
  

  
  I hope it helps.
  

  
  Best Regards,
  Dirso.

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• • Reply

  18 years ago

  by qwijibow

  Chris Stones

  England Nottingham, United Kingdom

  Joined 19 years ago

  eh ?
  you can actually increace the size of an array during runtime !! ??
  

  
  i was told you had to specify the max length of an array in the code, and it was fixed.

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• • Reply

  18 years ago

  by dirso

  Edilson

  Campinas, Brazil, Brazil

  Joined 19 years ago

  U can allocate memory how many times u want to.
  

  
  Just 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 */
   }
  };
  

  
  Best Regards,
  Dirso

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