(C++) boost::dynamic_pointer_cast

 

boost::dynamic_pointer_cast is a template function to dynamic_cast on a boost::shared_ptr.

 

• Download the Qt Creator project 'CppDynamic_pointer_cast' (zip)

 

 

 

 

 

Technical facts

 

Application type(s)

• Desktop application

Operating system(s) or programming environment(s)

• Lubuntu 13.04 (raring)

IDE(s):

• Qt Creator 2.7.0

Project type:

• Console application

C++ standard:

• C++98

Compiler(s):

• G++ 4.7.3

Libraries used:

• Boost: version 1.49
• STL: GNU ISO C++ Library, version 4.7.3

 

 

 

 

 

Qt project file: CppDynamic_pointer_cast.pro

 

---

TEMPLATE = app CONFIG += console CONFIG -= app_bundle CONFIG -= qt SOURCES += main.cpp

 

 

 

 

 

main.cpp

 

---

#include <cassert> #include <iostream> #include <boost/shared_ptr.hpp> struct Base {   virtual ~Base() {}   void BaseSayHi() const { std::cout << "Base says hi\n"; } }; struct Derived : public Base {   void DerivedSayHi() const { std::cout << "Derived says hi\n"; } }; int main() {   //Base initialized with derived, can be downcasted to derived   {     const boost::shared_ptr<Base> p1(new Derived);     const boost::shared_ptr<Derived> p2(boost::dynamic_pointer_cast<Derived>(p1));     assert(p1);     assert(p2);     assert(p1 == p2);     assert(p1.use_count() == 2);     assert(p2.use_count() == 2);   }   //Base initialized with base, cannot be downcasted to derived   {     const boost::shared_ptr<Base> p1(new Base);     const boost::shared_ptr<Derived> p2(boost::dynamic_pointer_cast<Derived>(p1));     assert( p1);     assert(!p2);     assert(p1 != p2);     assert(p1.use_count() == 1);   }   //Const base initialized with derived, can be downcasted to const derived   {     const boost::shared_ptr<const Base> p1(new Derived);     const boost::shared_ptr<const Derived> p2(boost::dynamic_pointer_cast<const Derived>(p1));     assert(p1);     assert(p2);     assert(p1 == p2);     assert(p1.use_count() == 2);     assert(p2.use_count() == 2);   }   //Const base initialized with base, cannot be downcasted to const derived   {     const boost::shared_ptr<const Base> p1(new Base);     const boost::shared_ptr<const Derived> p2(boost::dynamic_pointer_cast<const Derived>(p1));     assert( p1);     assert(!p2);     assert(p1 != p2);     assert(p1.use_count() == 1);   }   //Const base initialized with derived, cannot be down- and const-casted to non-const derived   {     const boost::shared_ptr<const Base> p1(new Derived);     //Removing const: will and should not compile     //const boost::shared_ptr<Derived> p2(boost::dynamic_pointer_cast<Derived>(p1));     assert(p1);   }   //Base initialized with derived, can be downcasted to const derived with adding constness   {     const boost::shared_ptr<Base> p1(new Derived);     //Adding const: will and should compile     const boost::shared_ptr<const Derived> p2(boost::dynamic_pointer_cast<const Derived>(p1));     assert(p1);     assert(p2);     assert(p1 == p2);     assert(p1.use_count() == 2);     assert(p2.use_count() == 2);   }   //Delete one of the two instances   for (int i=0; i!=2; ++i)   {     boost::shared_ptr<Base> p1(new Derived);     boost::shared_ptr<Derived> p2(boost::dynamic_pointer_cast<Derived>(p1));     assert(p1);     assert(p2);     assert(p1 == p2);     assert(p1.use_count() == 2);     assert(p2.use_count() == 2);     if (i % 2)     {       p1.reset(new Base);     }     else     {       p2.reset(new Derived);     }     assert(p1 != p2);     assert(p1.use_count() == 1);     assert(p2.use_count() == 1);   } }