Re: [Arianne-general] [C++]STL questions

[Max H. <ma...@qu...>]

At 20:56 Uhr +0100 21.01.2001, MIGUEL ANGEL BLANCH LARDIN wrote:
>Hi, ( Uli )
>
>I have been taking a look again to my C++ book on a free hour that I
>have.
>I have some questions:
>STL containers don't use pointer, so if I have to insert a subclass,
>what I do? as if I insert the subclass I am going to lose it.

If you need to insert subclasses, you have to go with pointers rather 
than direct objects.

E.g. use std::list<Object*> instead of std::list<Object>. Then you 
can insert Object*, MyObjectSubClass* etc.
Drawback is that you have to delete the objects yourself on clear etc...

However, it would be feasible to write a simple (template) subclass 
of std::list which would just do this all for you.

This class would be used like AList<Object> but internally would use 
a std::list<Object*> (note the added *)

E.g.
template<class T>
class AList : public std::list<T*> // note:
{
   typedef std::list<T*>  _base;
   AList() : _base() {}
...
   void clear()
   {
     for(_base::const_iterator X = begin(); X != end(); ++X)
       delete *X;
     _base::clear();
   }
...
};


In fact, it might be better to use a HAS-A relation here than an IS-A 
relation...




Max
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Max Horn
C/C++ Developer

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