[reSIProcate] VS2005 crashing with DUM

[Adam Roach]

On 10/23/07 11:00 PM, Adam Roach wrote:
> david Butcher wrote:
>   
>> auto_ptr is not compatible with virtual destructors. that may be the odd bit.
>>   
>>     
>
> What?
>
>   

Let me be more explicit.

Stroustrup [1] doesn't mention anything about this in his treatment of 
auto_ptr. In fact, his examples include putting the base class of 
polymorphic objects into auto_ptrs -- which is going to lead to improper 
release of resources without virtual destructors.

Also, extensive searches on Google failed to turn anything up that might 
be interpreted as a general prohibition against using auto_ptr with 
objects that have virtual destructors.

In fact, the only thing I turned up has to do with a really obscure bug 
in Visual C++ 8.0, apparently having to do with errant coercion paths 
[2]; it sound like it impacts all virtual methods, not just destructors. 
It should be noted that the code that causes these problems shouldn't 
compile under real C++ compilers (although I suppose there's a chance 
that this coercion path is preferred by the compiler over another 
implicit path that other compilers use for the specific code in question 
-- meaning it would compile in both environments, but trigger the 
"virtual methods crash" bug described in the article I cite).

Finally, I've demonstrated to myself that things work just fine with 
auto_ptr and virtual destructors under g++ in the trivial case with a 
tiny program:

#include <iostream>
#include <memory>

class A
{
  public:
    A(){}
    virtual ~A();
};

A::~A()
{
  std::cout << "A is going away" << std::endl;
}

class B : public A
{
  public:
    B(){}
    virtual ~B();
};

B::~B()
{
  std::cout << "B is going away" << std::endl;
}

int main(int argc, char **argv)
{
  std::auto_ptr<A> ptr(new B());
  ptr.reset();
  return 0;
}


So, david: could you please clarify what you mean? It's not clear to me, 
and I've had a number of developers send me private mail asking, "is 
this right?"

/a

---
[1] Soustrup, Bjarne, "The C++ Programming Language", 3rd Edition, 
Addison Wesley, 1997

[2] Bottom of page: 
<http://www.codeproject.com/Feature/SubtleBugs.asp?select=2053685&df=100&forumid=343280&exp=0&fr=183.5>