Marc Ferry <marc@netmansys.fr> wrote in article <35867306.F1A70DF6@netmansys.fr>...
> I am getting confused about the erase() method of a list.
> I would like to remove (and delete) the first element of
> a list containing pointers. Among the following methods,
> which one do you suggest ?
>
> void X::removeAndDeleteFirst(list<A*>& a_ptr_list)
> {
>   list<A*>::iterator it = a_ptr_list.begin();
>   a_ptr_list.erase(it);
>   // Memory leak ?

Yes, try instead:

if (it != a_ptr_list.end())
 {delete **it;
 a_ptr_list.erase(it); }

ASSUMING that each element of the list ``owns'' the object designated
by the pointer it stores. (The designated object should die when the
pointer dies.)

> void X::removeAndDeleteFirst(list<A*>& a_ptr_list)
> {
>   list<A*>::iterator it = a_ptr_list.begin();
>   delete it;

DISASTROUS. You're deleting an automatic object.

>   a_ptr_list.erase(it);
> }
>
> void X::removeAndDeleteFirst(list<A*>& a_ptr_list)
> {
>   list<A*>::iterator it = a_ptr_list.begin();
>   A *a = *it;
>   a_ptr_list.erase(it);
>   delete a;

This is an acceptable variation of what I showed above, except that
you really should test for an empty list.

> In other words, does the call to erase() also remove the
> pointed object, or should a delete be called on the pointed
> object ?

Trust the list to delete any object it stores. In this case, it stores a
pointer, so deleting it does nothing. As always, it's up to you, the
programmer, to know what to do (if anything) with the object pointed
at (if any).

>            In the second case, when should it be done (after
> or before the call to erase()) ?

Doesn't matter, unless you're worrying about keeping the list in
a coherent state in a multithreaded environment, in which case
you have LOTS more to worry about.

P.J. Plauger
Dinkumware, Ltd.
http://www.dinkumware.com
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