Re: virtual operator +

"Maarten Kronenburg" <>
Tue, 11 Sep 2007 21:33:22 +0200

Bull's eye... my base class has no data members and derived class have
all the members
the design is like
class Base_string{};

Class Char_string:Base_string
{ char d_the_string[size];
                   size_t d_size;
Class Hash_string:Base_string
{ char d_the_string[size];
  size_t d_size;
  int d_hash; };

so here i'm stuck while overriding the virtual operator+ in the
Base_string as it would mess up what it is pointing to (eg in the
earlier post)

Personally I understand that the hashed string has different addition
behaviour than a normal string. But personally for reasons of simplicity I
would make a single class hash_string which always has a data member int
d_hash, but when d_hash is zero, the class behaves like a normal string, and
I would make the size not a template parameter, but a constructor parameter,
but also use a char type template parameter.
Just as another line of thought:
template<class charT>
class hash_string
{ charT * the_string;
  size_t the_size;
  unsigned int the_hash;
  hash_string( size_t asize, unsigned int ahash = 0 )
   : the_size( asize ), the_hash( ahash )
  { the_string = new charT [ asize ];
  { delete [] the_string;
Now the member functions and operators like operator+= do a hash only if
the_hash is not zero. You would have to decide what the binary operator+
must do when only one of the arguments the_hash is zero, or when they are
different. This way you don't need derivation at all, which in my opinion in
this case saves you some problems.
Regards, Maarten.

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