On Apr 25, 9:53 am, rwf_20 <rfr...@[EMAIL PROTECTED]
> wrote:
>
> myClass::myClass() : m_pimpl(std::auto_ptr<myStruct>(new myStruct()))
> { }
You should be able to simplify that to
myClass::myClass() : m_pimpl(new myStruct())
{ }
> This compiles just fine, until I try to use myClass elsewhere. At
> this point, I get warnings like:
>
> "deletion of pointer to incomplete type 'myStruct'; no destructor
> called"
>
> I guess I understand why this happens, and it's fixed by declaring a
> destructor for myClass and defining it in the .cpp file. It just irks
> me that I need to define a blank destructor (the same thing the
> compiler should generate) to make this work.
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.
The problem is that if you don't define the destructor in the cpp, the
compilers implicit definition will be used. This implicit definition
will be as if it were declared inline in the header file. The
destructor for myClass will call the destructor for the auto_ptr,
which will call delete on a pointer to the incomplete type
myClass::myStruct. The result is undefined behavior.
If you define the destructor of myClass after the definition of the
nested class myClass::myStruct, then everything will work as expected
and you'll avoid the warning that you are seeing.
> Googling this issue, I
> findhttp://www.gotw.ca/publications/using_auto_ptr_effectively.htm,
> in which Mr. Sutter demonstrates this same code and adds the comment:
>
> "In fact, if there's no other reason for explicitly writing a
> destructor, we don't need to bother with a custom destructor at all
> any more."
>
This is one of the 'other reasons' he is talking about. It is a
special case.
Travis
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