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Re: Any way to detect the absense of virtual destructor in base class?

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On 25.11.2011 19:30, Juha Nieminen wrote:
> Alf P. Steinbach<alf.p.steinbach+usenet@gmail.com>  wrote:
>> Use `std::unique_ptr` or `std::shared_ptr`, or e.g. `boost::shared_ptr`.
>>
>> These smart pointers remember the proper derived class destruction to
>> use, freeing you having to have a virtual destructor.
>
>    How exactly do they achieve that? If I do, for example, this:
>
>      std::unique_ptr<Base*>  ptr = new Derived;
>
> then how exactly is 'ptr' able to deduce the derived class destructor in
> order to directly call it when it disposes of the object?
>
>    (And where would it store it anyways? I thought the whole idea with
> std::unique_ptr is that its size is that of one pointer, hence making
> it as efficient as a raw pointer.)
>
>    I wonder if you are being confused by shared_ptr (and possible other
> smart pointers) being able to destroy an object even if they only see
> a class declaration (rather than a definition), as long as the class was
> fully declared at the point of construction of the pointer. (IOW the class
> doesn't need to be fully declared at the place of destruction.) That's not
> the same thing as a base-class type smart pointer being able to deduce
> the derived-class type destructor.

I'm looking at N3290, which I believe is identical to the final standard.

And there std::unique_ptr stores a deleter, which can be function object 
or a function pointer or whatever, specified in constructor call.

Essentially it's the same idea as for shared_ptr's deleter except that 
that unique_ptr doesn't use templating to infer the real type of the 
object pointer it gets, so one has to write like

   unique_ptr<Base> p = unique_ptr<Derived>( new Derived );

The only trouble is, I can't get the deleter functionality to work with 
either Visual C++ 10.0 or g++ 4.4.1 in Windows, nor with g++ 4.6.1 in 
Ubuntu.

That might indicate that my understanding is wrong (in which case the 
deleter argument then seems worthless), or that unique_ptr is not fully 
implemented by these compilers, or that N3290 is not identical to C++11?


Cheers, & thanks for focusing me on that,

- Alf

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Thread

Any way to detect the absense of virtual destructor in base class? Qi <no@no.no> - 2011-11-24 17:20 +0800
  Re: Any way to detect the absense of virtual destructor in base class? "Alf P. Steinbach" <alf.p.steinbach+usenet@gmail.com> - 2011-11-24 10:35 +0100
    Re: Any way to detect the absense of virtual destructor in base class? Qi <no@no.com> - 2011-11-24 21:05 +0800
    Re: Any way to detect the absense of virtual destructor in base class? Juha Nieminen <nospam@thanks.invalid> - 2011-11-25 18:30 +0000
      Re: Any way to detect the absense of virtual destructor in base class? "Alf P. Steinbach" <alf.p.steinbach+usenet@gmail.com> - 2011-11-25 22:25 +0100
        Re: Any way to detect the absense of virtual destructor in base class? "Alf P. Steinbach" <alf.p.steinbach+usenet@gmail.com> - 2011-11-25 22:40 +0100
        Re: Any way to detect the absense of virtual destructor in base class? Juha Nieminen <nospam@thanks.invalid> - 2011-11-25 22:30 +0000
          Re: Any way to detect the absense of virtual destructor in base class? "Alf P. Steinbach" <alf.p.steinbach+usenet@gmail.com> - 2011-11-26 01:36 +0100
            Re: Any way to detect the absense of virtual destructor in base class? Juha Nieminen <nospam@thanks.invalid> - 2011-11-26 12:16 +0000
  Re: Any way to detect the absense of virtual destructor in base class? Vladimir Jovic <vladaspams@gmail.com> - 2011-11-24 10:45 +0100
    Re: Any way to detect the absense of virtual destructor in base class? Qi <no@no.com> - 2011-11-24 21:07 +0800
  Re: Any way to detect the absense of virtual destructor in base class? SG <s.gesemann@gmail.com> - 2011-11-24 04:50 -0800
    Re: Any way to detect the absense of virtual destructor in base class? Qi <no@no.com> - 2011-11-24 21:04 +0800
      Re: Any way to detect the absense of virtual destructor in base class? Marc <marc.glisse@gmail.com> - 2011-11-24 16:12 +0000
  Re: Any way to detect the absense of virtual destructor in base class? Lee Steven <steven.mtl@gmail.com> - 2011-11-25 06:55 -0800
  Re: Any way to detect the absense of virtual destructor in base class? jgk@panix.com (Joe keane) - 2011-11-25 22:21 +0000
    Re: Any way to detect the absense of virtual destructor in base class? Ian Collins <ian-news@hotmail.com> - 2011-11-26 11:32 +1300

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