Re: Destructor not called with forward declaration instead of include

On Apr 21, 7:43 pm, internetpet <internet...@[EMAIL PROTECTED]
> wrote:
> Say you have these files:
>
> BigClazz.h
>
>      class Clazz; // Note the forward declaration only , no include
> "Clazz.h"
>      class BigClazz
>      {
>          public:
>              BigClazz();
>              ~BigClazz();
>              Clazz* pclazz;
>      };
>
> BigClazz.cpp
>
>      #include "BigClazz.h"
>      BigClazz::BigClazz(){}
>      BigClazz::~BigClazz()
>      {
>          delete pclazz; // Here the destructor of of the Clazz object
> will not be called
>      }
>

<snip>

>
> If you run this you'll see that the Clazz destructor will not be
> called when BigClazz does "delete pclazz;" in it's own destructor. But
> if you replace the forward declaration in BigClazz (class Clazz;) with
> an include
> (#include "Clazz.h") then it works.
>
> Any idea why?

Because the C++ standard allows pointers to incomplete class types to
be deleted but if the class has a non-trivial destructor or a class
operator delete the behavior is undefined.

You can easily work around the problem by including Clazz.h into
Bigclazz.cpp so that the type you are deleting is complete at the
point you delete it.

Travis


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