Re: [boost] Re: Re: Is there any way to get typeid() to return the derived class name?

From: Jody Hagins (jody-boost-011304_at_[hidden])
Date: 2005-03-01 12:54:56

On Tue, 1 Mar 2005 09:31:21 -0800 (PST)
Chris Just <cpjust_at_[hidden]> wrote:

> I'm using MS Visual C++ 6.0.  This is what I'm doing:

Sorry ;-)

 
> CBase { ... };
> CDerived : public CBase { ... };
> 
> CSomething
> {
> public:
>    CSomething( const CBase&  base ) : m_Base( base ) {}
> 
>    CSomething& operator=( const CSomething&  rhs )
>    {
>       if ( typeid( m_Base ) != typeid( rhs.m_Base ) ) // This never
>       fails.{
>          throw exception();
>       }
>    }
> 
> private:
>    CBase&  m_Base;
> };
> 
> When I look at the type_info object's name(), it always returns
> "CBase", even if it's actually a CDerived object.

You have ommitted the most important pieces in your code sample...

#include <typeinfo>
#include <cassert>

struct np_base { };
struct np_derived : public np_base { };
struct base { virtual ~base() { } };
struct derived : public base { };

int main(int, char *[])
{
  np_derived npd;
  derived d;
  np_base * np_base_ptr = &npd;
  base * base_ptr = &d;
  assert(typeid(*np_base_ptr) == typeid(np_base));
  assert(typeid(*base_ptr) == typeid(derived));
  return 0;
}

Compile and run the above on your compiler.  If it fails, you have a
problem with your compiler.  Otherwise, you probably have a problem with
your code.  Note that you only get the most derived type, if the class
is polymorphic (i.e., has at least one virtual function).