Re: vectors and polymorphism

From:

Carl Barron <cbarron413@adelphia.net>

Newsgroups:

comp.lang.c++.moderated

Date:

Tue, 7 Aug 2007 22:34:01 CST

Message-ID:

<070820072108549886%cbarron413@adelphia.net>

In article <1186514192.273353.140920@w3g2000hsg.googlegroups.com>,
<webmaster@developerland.com> wrote:

I have a vector with A and B elements on it , how can I retrieve B
elements only from col ?

class A
{
}

class B : public A
{
}

void main ()
{
   std::vector<A*> col;

  col.push_back (new A());
  col.push_back (new B());
  col.push_back (new A());
  col.push_back (new A());
  col.push_back (new B());
}

off the cuff:
   struct save_B:std::iterator<std::output_iterator_tag,
      void,void,void,void>
   {
      std::vector<B*> *out;
      save_B(std::vector<B*> &a):out(&a){}
      save_B & operator = (A *a)
      {
         B*b = dynamic_cast<B*>(a);
         if(b) out->push_back(b);
         return *this;
      }
      save_B & operator *() {return *this;}
      save_B & operator ++() {return *this;}
      save_B & operator ++(int) {return *this;}
   };

   //
   std::vector<B*> Bs;
   std:;copy(col.begin(),col.end(),save_B(Bs));

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