casting shared pointers to derived classes
Greetings, all - I am updating a neural network package from the DOS days to modern C++ standards. I have a shared_ptr to a vector of shared_ptrs of type Layer. This class has derived classes OutputLayer, MiddleLayer and InputLayer. Each of these has their own method for calculating output updates, so I need to be able to cast. from boost::shared_ptr<Layer> to static_cast<OutputLayer*>(). Unfortunately, VC++ 2010 will not allow me to do so. It won't even allow a reinterpret_cast. I've looked on the Web and I also have Schalling's guide to Boost. Thank you in advance for your guidance. I'm using boost_1_47_0, if that makes a difference. :D
Cast a Layer to an OutputLayer: boost::shared_ptr<Layer> layer = getLayer(); boost::shared_ptr<OutputLayer> outputLayer = boost::dynamic_pointer_cast<OutputLayer>(layer); But please consider to declare your calculation method virtual and to provide different implementations in your derived classes. You would not have to cast at all then. Thomas -------- Original Message -------- Subject: [Boost-users] casting shared pointers to derived classes From: Don Wilde <donintel11@yahoo.com> To: boost-users@lists.boost.org <boost-users@lists.boost.org> Date: Wed Jan 11 2012 16:18:55 GMT+0100
Greetings, all - I am updating a neural network package from the DOS days to modern C++ standards. I have a shared_ptr to a vector of shared_ptrs of type Layer. This class has derived classes OutputLayer, MiddleLayer and InputLayer. Each of these has their own method for calculating output updates, so I need to be able to cast. from boost::shared_ptr<Layer> to static_cast<*>(). Unfortunately, VC++ 2010 will not allow me to do so. It won't even allow a reinterpret_cast. I've looked on the Web and I also have Schalling's guide to Boost. Thank you in advance for your guidance. I'm using boost_1_47_0, if that makes a difference. :D
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On 01/11/2012 05:17 PM, spam-receiver@web.de wrote:
Cast a Layer to an OutputLayer:
boost::shared_ptr<Layer> layer = getLayer(); boost::shared_ptr<OutputLayer> outputLayer = boost::dynamic_pointer_cast<OutputLayer>(layer); I wonder why is boost::detail::dynamic_cast_tag part of the detail namespace and not part of the public API instead. It seems it would be useful in this and similar cases.
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-- VZ
On Wed, Jan 11, 2012 at 4:18 PM, Don Wilde <donintel11@yahoo.com> wrote:
Greetings, all -
I am updating a neural network package from the DOS days to modern C++ standards.
I have a shared_ptr to a vector of shared_ptrs of type Layer. This class has derived classes OutputLayer, MiddleLayer and InputLayer. Each of these has their own method for calculating output updates, so I need to be able to cast. from boost::shared_ptr<Layer> to static_cast<OutputLayer*>().
Unfortunately, VC++ 2010 will not allow me to do so. It won't even allow a reinterpret_cast. I've looked on the Web and I also have Schalling's guide to Boost.
Not only VC++ does not allow this, but the C++ standard as well.
Thank you in advance for your guidance. I'm using boost_1_47_0, if that makes a difference. :D
Use tools provided by the shared_ptr itself... Take a look at http://www.boost.org/doc/libs/1_48_0/libs/smart_ptr/shared_ptr.htm#Synopsis, especially at these functions: template<class T, class U> shared_ptr<T> static_pointer_cast <http://www.boost.org/doc/libs/1_48_0/libs/smart_ptr/shared_ptr.htm#static_pointer_cast>(shared_ptr<U> const & r); // never throws template<class T, class U> shared_ptr<T> const_pointer_cast <http://www.boost.org/doc/libs/1_48_0/libs/smart_ptr/shared_ptr.htm#const_pointer_cast>(shared_ptr<U> const & r); // never throws template<class T, class U> shared_ptr<T> dynamic_pointer_cast <http://www.boost.org/doc/libs/1_48_0/libs/smart_ptr/shared_ptr.htm#dynamic_pointer_cast>(shared_ptr<U> const & r); // never throws Greetings, Ovanes
[snip] Use tools provided by the shared_ptr itself... Take a look at http://www.boost.org/doc/libs/1_48_0/libs/smart_ptr/shared_ptr.htm#Synopsis, especially at these functions: template<class T, class U> shared_ptr<T> static_pointer_cast(shared_ptr<U> const & r); // never throws template<class T, class U> shared_ptr<T> const_pointer_cast(shared_ptr<U> const & r); // never throws template<class T, class U> shared_ptr<T> dynamic_pointer_cast(shared_ptr<U> const & r); // never throws [snip] Thank you Ovanes and Thomas for your insights! I appreciate the help. :D
participants (4)
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Don Wilde -
Ovanes Markarian -
spam-receiver＠web.de -
Václav Zeman