2. String Class Varieties

The string class is the most vital object in programming, and string manipulations are most extensively used and they comprise of 20 to 60% of total code. There are 3 variety of string classes. Ofcourse, you can build your own string class by simply inheriting from these string classes -

• String class given in this document Appendix A String.h

• GNU string class
  • GNU C++ Library - Univ of Tech, Sydney http://www.socs.uts.edu.au/doc/gnuinfo/libg++/libg++_18.html and user's guide
  • mirror site Gesellschaft http://www-aix.gsi.de/doc/gnu/libg++_18.html#SEC23 and user's guide
  • mirror site Techno, Russia http://www.techno.spb.ru/~xbatob/FAQ/GNU/libg++_19.html#SEC27 and user's guide
  • mirror site Univ of Utah http://www.math.utah.edu/docs/info/libg++_19.html#SEC27 and user's guide

• Qt String class at http://doc.trolltech.com/qstring.html mirror at http://www.cs.berkeley.edu/~dmartin/qt/qstring.html

• If none of these alternatives are suitable, you can build your own string class. You can start with one or more of the pre-built classes listed above (by using single or multiple inheritance.)

2.1 Multiple Inheritance - Sample Custom String class

As mentioned above, you can build your own custom string class from the pre-built classes by single or multiple inheritance. In this section we will build a sample custom string class by using multiple inheritance, inheriting from the GNU string class and the string class presented in Appendix H.

Start by downloading the sample file 'string_multi.h' from Appendix A . That file is reproduced below:

// ******************************************************************
// Sample program to demonstrate constructing your own string class
// by deriving from the String class and stdlib's "string" class
// ******************************************************************

#ifndef __STRING_MULTI_H_
#define __STRING_MULTI_H_

#include <string>
#include "String.h"

// Important Notes: In C++ the constructors, destructors and copy 
//       operator are NOT inherited by the derived classes!!
//       Hence, if the operators like =, + etc.. are defined in
//       base class and those operators use the base class's contructors
//       then you MUST define equivalent constructors in the derived 
//       class. See the sample given below where constructors mystring(), 
//       mystring(char[]) are defined.
//
//       Also when you use operator as in atmpstr + mstr, what you are really
//       calling is atmpstr.operator+(mstr). The atmpstr is declared a mystring

class mystring:public String, string
{
        public:
                mystring():String() {}  // These are needed for operator=, +
                mystring(char bb[]):String(bb) {}  // These are needed for operator=, +
                mystring(char bb[], int start, int slength):String(bb, start, slength) {}
                mystring(int bb):String(bb) {}  // needed by operator+
                mystring(unsigned long bb):String(bb) {}  // needed by operator+
                mystring(long bb):String(bb) {}  // needed by operator+
                mystring(float bb):String(bb) {}  // needed by operator+
                mystring(double bb):String(bb) {}  // needed by operator+
                mystring(const String & rhs):String(rhs) {}  // Copy Constructor needed by operator+
                mystring(StringBuffer sb):String(sb) {}  // Java compatibility
                mystring(int bb, bool dummy):String(bb, dummy) {}  // for StringBuffer class

                int mystraa; // customizations of mystring
        private:
                int mystrbb; // customizations of mystring
};

#endif // __STRING_MULTI_H_