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);

  }

}

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(C++) boost::dynamic_pointer_cast

Technical facts

Qt project file: CppDynamic_pointer_cast.pro

main.cpp