Re: [Boost-users] shared_ptr vs ordinary pointers

From: Rene Rivera (grafik.list_at_[hidden])
Date: 2005-11-26 14:19:31

Merrill Cornish wrote:
> With an ordinary C++ pointer, if I have a BaseClass and a DerivedClass derived
> from BaseClass, then I can do
> 
>     BaseClass* objectPtr;
>     objectPtr = new DerivedClass();
> 
> Later, if BaseClass has a virtual destructor, I can call delete(objectPtr) and the
> DerivedClass destructor will be called.
> 
> Now, does this work with shared_ptr?
> 
>     shared_ptr<BaseClass> objectPtr;
>     objectPtr = shared_ptr<DerivedClass>(new DerivedClass());

Yes.

> and later, delete(objectPtr).

No, but it's because of C++ rules not shared_ptr rules ;-) When the 
objectPtr goes out of scope the pointee is deleted.

> Does any of the magic going on behind the scenes prevent shared_ptrs from
> being used like this?

It's designed to work like a regular ptr. Make sure to read the docs:

http://www.boost.org/libs/smart_ptr/shared_ptr.htm

Pay special attention to the TR1 functions 
<http://www.boost.org/libs/smart_ptr/shared_ptr.htm#functions> for 
pointer conversions: static_pointer_cast, const_pointer_cast, and 
dynamic_pointer_cast.

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