auto_ptr's exception safe

[Kuba_O]

Hello, i've got simple question about std::auto_ptr: what makes it is
exceptions safe?
Lets say i have class "int_smart_ptr" implemented like this:

class int_smart_ptr
{
private:
int *int_obj;
public:
explicit int_smart_ptr(int *_p)throw():int_obj(_p){}
~int_smart_ptr()throw(){delete int_obj;}
};

Is this class exception safe? When exception occur in scope in
int_smart_ptr was use, would destructor be call?
If yes, why?
If not, what feature of std::auto_ptr decide it is safe in case of
exception?

I hope someone understand my english

Regards
Kuba

 

[Michiel.Salters]

Hello, i've got simple question about std::auto_ptr: what makes it is
exceptions safe?

Simple: a proper copy ctor, assignment and destructor.

Lets say i have class "int_smart_ptr" implemented like this:

class int_smart_ptr
{
private:
int *int_obj;
public:
explicit int_smart_ptr(int *_p)throw():int_obj(_p){}
~int_smart_ptr()throw(){delete int_obj;}
};

Is this class exception safe?

No. If you copy one, and an exception is thrown, both the original and
the copy will be destroyed. Both destructors will attempt to delete the
same int*, leading to a double-deletion bug.

When exception occur in scope in int_smart_ptr was use, would
destructor be call? If yes, why?

Yes, because destructors are always called for all objects from the
scope being exited. Of course, auto_ptr has a copy ctor and an
operator= defined which avoid the double-deletion bug you have.

HTH,
Michiel Salters

 

[Kuba_O]

25.01.2006, (e-mail address removed):

No. If you copy one, and an exception is thrown, both the original and
the copy will be destroyed. Both destructors will attempt to delete the
same int*, leading to a double-deletion bug.

I know that, it was just simple sample

Yes, because destructors are always called for all objects from the
scope being exited.

I did not know that, now everything is clear.
Thanks for inform me about such essential behavior of exceptions

Of course, auto_ptr has a copy ctor and an
operator= defined which avoid the double-deletion bug you have.

Yeap.

out.