Vector, polymorphism, new and returns

[XanaRaquel]

I'm getting a little confused to what to do here.
There's a lot going on my code so I'll try to simplify it with just my confusing/problem.

class A
{
  char letter;
  A() { letter = 'a';}
  ...
};

class B : public A
{
  B() { setLetter('b'); }
  ...
};

class C : public A
{
  C() { setLetter('c'); }
 ...
};

class Infos
{
  ...
  vector<A *> letters;

  Infos(){
    letters.push_back(new A());
    letters.push_back(new B());
    letters.push_back(new C());
  }
  ...
  ...
  A * doSomething(char x)
  {
    vector<A *>::iterator it;
	for (it = letters.begin(); it != letters.end(); ++it)
		if ((*it)->getLetter() == x)
			return (*it);
  }
};

class Work
{
  Infos infos;
  ...
  ...
  ...
  B * doWork()
  {
     ...
     return new B(infos.doSomething('b'));
  }
};

This is basically what I have. My problem is the return in doWork(). It won't allow it to be like that even if doSomething('b') is actually returning a B (or at least I think it is).
I tried
return new B((B *)infos.doSomething('b'));
but it didn't work either.
Any lights on this?

[LB]

Look up dynamic_cast - just keep in mind the fact that you even need to do this at all means you have a design flaw. Why not have a doWork function in A? Then you need not care whether it's an A, B, or C.

[XanaRaquel]

Hum, how? I'm not seeing how it would work.
DoWork() needs to return a B that is a copy of a B that exists in that vector.

[TwilightSpectre]

As @L B said, why not dynamic_cast: You can use it to cast a base into a derived, with run-time type checking. Just make sure to put it into a try-catch block to catch std::bad_casts.

See http://www.cplusplus.com/reference/typeinfo/bad_cast/

EDIT:
Sorry, if you are using pointers I don't think you need to check for std::bad_cast, just check to see if a nullptr has been returned instead.

[XanaRaquel]

I tried dynamic_cast but got curious on his alternative.

Using dynamic_cast I ended up with something like this:

return new B( *(dynamic_cast<B *>(infos.doSomething('b')) );

I don't know if this is correct or not. At least the compiler doesn't give me any errors. I can't test for now because I have to finish other parts of the code.

[LB]

Oh, if you want to get a copy, you should use the Clone Pattern.

[XanaRaquel]

I don't think I'm allowed to use that. This is part of a programming class' project and I don't recall the teacher ever talking about that.

Casts however he did talk about and dynamic_cast is doing the trick for now.

Thanks!!

[LB]

The Clone Pattern isn't exactly a feature of C++, it's just something you can do within the bounds of the language. I would be extremely surprised if your teacher wanted you not to do something similar to it.