Dynamic Casting Problem

**nickman** · 10-10-2013

Hi

I was trying to learn dynamic casting and saw some strange behavior.
My program was crashed as exception is thrown as bad typeid.

Below is code:

Code:

#include<iostream>
#include <exception>

using namespace std;

class base
{
public:
 virtual void show()
	{
		cout<<"inside base";
	}
};

class derived: public base
{
public:
	void show()
	{
		cout<<"inside derived";
	}
};

int main()
{
   //base *a;
    derived *d;
	try
	{
       base *a = dynamic_cast<derived*>(d);
	   throw bad_typeid();
	 }
	catch(...)
	{
		cout<<"bad_typeid";
	}

I know that we do upcasting as derived is inherited from base.
So why this is failing. Can any body le me know what I am missing here?

Thanks
Nickman

**grumpy** · 10-10-2013

Look at line 31. Is there any way that a bad_typeid would NOT be thrown?

The dynamic_cast you're doing converts a derived * into a derived *. That does nothing. Similarly, a derived * is implicitly converted to a base *.

Unrelated to the problem you asked about, but bad_typeid is specified as being declared declared in the <typeinfo> header, not <exception> or <typeinfo>.

**Elysia** · 10-10-2013

Also, d is pointing to nowhere valid.

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