std::unique_ptr with derived class

Question

I have a question about the c++11 pointers. Specifically, how do you turn a unique pointer for the base class into the derived class?

class Base
{
public:
   int foo;
}

class Derived : public Base
{
public:
   int bar;
}

...

std::unique_ptr<Base> basePointer(new Derived);
// now, how do I access the bar member?

it should be possible, but I can't figure out how. Every time I try using the

basePointer.get()

I end up with the executable crashing.

Thanks in advance, any advice would be appreciated.

Answer 1

If they are polymorphic types and you only need a pointer to the derived type use dynamic_cast :

Derived *derivedPointer = dynamic_cast<Derived*>(basePointer.get());

If they are not polymorphic types only need a pointer to the derived type use static_cast and hope for the best:

Derived *derivedPointer = static_cast<Derived*>(basePointer.get());

If you need to convert a unique_ptr containing a polymorphic type:

Derived *tmp = dynamic_cast<Derived*>(basePointer.get());
std::unique_ptr<Derived> derivedPointer;
if(tmp != nullptr)
{
    basePointer.release();
    derivedPointer.reset(tmp);
}

If you need to convert unique_ptr containing a non-polymorphic type:

std::unique_ptr<Derived>
    derivedPointer(static_cast<Derived*>(basePointer.release()));