Dynamically choosing what to "new"

Hi,

I've run into a strange problem, but one that seems like it might be
fairly common.

I have a single base class, from which several other classes are derived.
To keep the example simple, the base class is "Animal" and the derived
classes are "Cat," "Dog," and "Horse."

The base class has a pure virtual method:

   virtual void GetName(std::string *s) = 0;

All the derived classes are required to implement this method and return
the appropriate string, for example:

   void Dog::GetName(std::string *s)
   {
      *s = "Dog";
   }

So when the user clicks a "Save" button, a text file is written by
calling the GetName() method on all the existing Animal objects. So the
file on disk would look something like this:

   Dog, Cat, Dog, Dog, Horse, Cat

Later, when the user clicks a "Load" button, I'd like to recreate all
those animals. What's a clean way to do this? My first thought was just
to test each string with a big if-else block, like so:

   while (ReadNextToken(input_string))
   {
      Animal *a;

      if (input_string == "Dog")
      {
         a = new Dog;
      }
      else if (input_string == "Cat")
      {
         a = new Cat;
      }
      else if (input_string == "Horse")
      {
         a = new Horse;
      }
      else
      {
         ErrorMessage()
      }
   }

But that's ugly and not object-oriented at all. It's also error-prone as
I add more and more classes, because I have to remember to manually add a
new "else if" block for every new class and I have to manually ensure
that the strings match the GetName() result.

Any ideas for a better approach would be appreciated.

Thanks,
Pat