Visual C++ .NET/Class/Casting

Casting class

<source lang="csharp">

1. include "stdafx.h"

using namespace System; ref class A {}; ref class B : public A {}; ref class C {}; void main() {

   Object ^v1 = gcnew A();              
   Object ^v2 = gcnew B();           
   Object ^v3 = gcnew C();         
   A ^a1 = gcnew A();               
   A ^a2 = gcnew B();
   A ^a3 = dynamic_cast<A^>(v1);  // downcast
   A ^a4 = dynamic_cast<A^>(v2);  // downcast
   B ^b1 = gcnew B();
   B ^b2 = dynamic_cast<B^>(v2);  // downcast
   B ^b4 = dynamic_cast<B^>(a2);  // downcast
   
   C ^c1 = gcnew C();
   C ^c2 = dynamic_cast<C^>(v1);  // Fails c2 = null. Miss match classes
   C ^c3 = static_cast<C^>(v2);   // c3 has invalid value of type B class
   C ^c4 = safe_cast<C^>(v3);     // downcast
   C ^c5 = (C^)(v3);              // downcast

}

 </source>

Casting from object

<source lang="csharp">

1. include "stdafx.h"

using namespace System; using namespace System::Collections; ref class Book{

  public:
    Book(){ }
    Book(String^ _title) { Title = _title; }
    property String^ Title;

}; int main(){

  ArrayList^ theList = gcnew ArrayList();
  theList->Add( gcnew Book("Men") );
  Book^ book = safe_cast<Book^>( theList[0] );
  Console::WriteLine(book->Title );
  theList->Add( gcnew String("data"));
  try{
     book = safe_cast<Book^>( theList[1] );
  }catch(InvalidCastException^ e){
     Console::WriteLine("wrong type");
  }

}

 </source>

Checking casts

<source lang="csharp">

1. include "stdafx.h"

using namespace System; ref class Base {}; ref class Derived : Base {} ; int main(){

   Base^ b = gcnew Base();
   Derived^ d = gcnew Derived();
   try
   {
      d = safe_cast<Derived^>(b);
   }
   catch (InvalidCastException^ e)
   {
   }
   
   d = dynamic_cast<Derived^>(b);
   if (d == nullptr)
   {
   }

}

 </source>