static_cast with boost::shared_ptr?

Question

What is the equivalent of a static_cast with boost::shared_ptr?

In other words, how do I have to rewrite the following

Base* b = new Base();
Derived* d = static_cast<Derived*>(b);

when using shared_ptr?

boost::shared_ptr<Base> b(new Base());
boost::shared_ptr<Derived> d = ???

Answer 1

Use boost::static_pointer_cast:

boost::shared_ptr<Base> b(new Base());
boost::shared_ptr<Derived> d = boost::static_pointer_cast<Derived, Base>(b);

Answer 2

There are three cast operators for smart pointers: static_pointer_cast, dynamic_pointer_cast, and const_pointer_cast. They are either in namespace boost (provided by <boost/shared_ptr.hpp>) or namespace std::tr1 (provided either by Boost or by your compiler's TR1 implementation).

Answer 3

As a comment: if Derived does in fact derive from Base, then you should use a dynamic_pointer_cast rather than static casts. The system will have a chance of detecting when/if your cast is not correct.

Answer 4

It is worth to mention that the there is difference in the number of casting operators provided by Boost and implementations of TR1.

The TR1 does not define the third operator const_pointer_cast()