how to erase a list member with just an iterator (without the list itself)?

[alon]

I got the following situation: I have a few lists of integers, and I
have an iterator pointing to one of the elements. I don't have a
pointer to the list itself ! All I want is to remove the element the
iterator points to...

Basically, a list element has pointers back and forth, so I shouldn't
need the list itself, but I don't see any function that does the work.
Is there a real problem to do this? Is it just a coincidence that no
body implemented such a function?

 

[alon]

Should make it clear - talking about STL list..

 

[Milind]

Hi,

http://www.sgi.com/tech/stl/List.html
This says, there is a erase function. and it says it does exactly what
you are expecting out of it..

Couldn't get your question really.

~M

 

[alon]

I'll try and clarify my question:

The erase function requires a pointer to the list.
list<int> L;
list<int>::iterator iter;
L.erase(iter);

In my case there is no pointer to the list, so what I need is something
like this:
list<int>::erase(iter);

Does this clarify my question?

 

[red floyd]

I'll try and clarify my question:

The erase function requires a pointer to the list.

No, erase is a member function of the list, and therefore requires a
list object.

list<int> L;
list<int>::iterator iter;
L.erase(iter);

In my case there is no pointer to the list, so what I need is something
like this:
list<int>::erase(iter);

Nope. How does erase know what list to erase from? Again, erase is a
*MEMBER FUNCTION* and therefore requires the object.

 

[Daniel T.]

I got the following situation: I have a few lists of integers, and I
have an iterator pointing to one of the elements. I don't have a
pointer to the list itself ! All I want is to remove the element the
iterator points to...

Basically, a list element has pointers back and forth, so I shouldn't
need the list itself, but I don't see any function that does the work.
Is there a real problem to do this? Is it just a coincidence that no
body implemented such a function?

It cannot be done, and that was by design. Removing an element from a
list without notifying the list is poor practice and makes some list
optimizations difficult to implement. For example, a list may contain a
"size_" member variable in order to speed up the call to myList.size().
Removing a element without telling the list would corrupt that member.

Of course, if each list iterator had a pointer to the list it belonged
too, then it could be done, but the C++ committee apparently decided not
to do that.

 

[alon]

"if each list iterator had a pointer to the list " - in practice, this
is what I ended up doing

Thx,
Alon