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()));