list erase without invalidating iterator

[catphive.lists]

Is there a way to call erase(iter) on a list without invalidating the
iterator? Can I make a copy of an iterator and then move forward the
original without moving the copy? I'm aware of the existence of
remove_if, but in the case I'm dealing with it would be much more
natural to use an iterator.

[Mark P]

ca************@ gmail.com wrote:

Is there a way to call erase(iter) on a list without invalidating the
iterator? Can I make a copy of an iterator and then move forward the
original without moving the copy? I'm aware of the existence of
remove_if, but in the case I'm dealing with it would be much more
natural to use an iterator.

Probably what you want is one of:

erase( iter++);
erase( iter--);

[David Harmon]

On 1 Dec 2006 18:46:59 -0800 in comp.lang.c++, ca************@ gmail.com
wrote,

>Is there a way to call erase(iter) on a list without invalidating the
iterator?

No. The iterator points to the element you are erasing; afterwards the
element is gone. You can't have a valid iterator pointing to a gone
element.

Can I make a copy of an iterator and then move forward the
original without moving the copy?

Sure, but remember that erase() returns the next iterator value, which
is probably what you want to use.

[Jim Langston]

<ca************ @gmail.comwrote in message
news:11******** *************@7 3g2000cwn.googl egroups.com...

Is there a way to call erase(iter) on a list without invalidating the
iterator? Can I make a copy of an iterator and then move forward the
original without moving the copy? I'm aware of the existence of
remove_if, but in the case I'm dealing with it would be much more
natural to use an iterator.

iter = MyContainer.era se(whatever);

iter will automatcially get incremented to the next element. So you don't
want to increment it in your for loop. Algorithm I use is:

for ( MyContainerType ::iterator it = MyContainer.beg in(); it !=
MyContainer.end (); )
{
if ( (*it).somecondi tion() == somethingelse )
it = MyContainer.era se( it );
else
++it;
}

[Howard]

"Mark P" <us****@fall200 5REMOVE.fastmai lCAPS.fmwrote in message
news:O_******** *********@newss vr21.news.prodi gy.net...

ca************@ gmail.com wrote:

>Is there a way to call erase(iter) on a list without invalidating the
iterator? Can I make a copy of an iterator and then move forward the
original without moving the copy? I'm aware of the existence of
remove_if, but in the case I'm dealing with it would be much more
natural to use an iterator.

Probably what you want is one of:

erase( iter++);
erase( iter--);

That's not going to work is it? I think that incrementing in invalidated
iterator is just as invalid as using it again.

But the erase function returns an iterator you can use after the erase
(pointing to the next item), so just do:

iter = erase(iter);

-Howard

[Victor Bazarov]

Howard wrote:

"Mark P" <us****@fall200 5REMOVE.fastmai lCAPS.fmwrote in message
news:O_******** *********@newss vr21.news.prodi gy.net...

>ca************@ gmail.com wrote:

>>Is there a way to call erase(iter) on a list without invalidating
the iterator? Can I make a copy of an iterator and then move
forward the original without moving the copy? I'm aware of the
existence of remove_if, but in the case I'm dealing with it would
be much more natural to use an iterator.

Probably what you want is one of:

erase( iter++);
erase( iter--);

That's not going to work is it? I think that incrementing in
invalidated iterator is just as invalid as using it again.

Nope. The iterator [still valid] is incremented just before the old
value (copied into a temporary object) is passed to the 'erase' function.
At the time of the function taking the necessary steps to remove the
element to which the iterator (passed into the function) points, the
iterator outside the function ('iter' variable) is pointing to the next
element. And that iterator is not going to be invalidated during the
erasure operation.

But the erase function returns an iterator you can use after the erase
(pointing to the next item), so just do:

iter = erase(iter);

Yes. It doesn't change the fact that 'erase(iter++)' is a valid way
to do it, though.

V
--
Please remove capital 'A's when replying by e-mail
I do not respond to top-posted replies, please don't ask

[Howard]

"Victor Bazarov" <v.********@com Acast.netwrote in message
news:el******** **@news.datemas .de...

Howard wrote:

>"Mark P" <us****@fall200 5REMOVE.fastmai lCAPS.fmwrote in message
news:O_******* **********@news svr21.news.prod igy.net...

>>ca************@ gmail.com wrote:
Is there a way to call erase(iter) on a list without invalidating
the iterator? Can I make a copy of an iterator and then move
forward the original without moving the copy? I'm aware of the
existence of remove_if, but in the case I'm dealing with it would
be much more natural to use an iterator.
Probably what you want is one of:

erase( iter++);
erase( iter--);

That's not going to work is it? I think that incrementing in
invalidated iterator is just as invalid as using it again.

Nope. The iterator [still valid] is incremented just before the old
value (copied into a temporary object) is passed to the 'erase' function.
At the time of the function taking the necessary steps to remove the
element to which the iterator (passed into the function) points, the
iterator outside the function ('iter' variable) is pointing to the next
element. And that iterator is not going to be invalidated during the
erasure operation.

Ah, ok.

>

>But the erase function returns an iterator you can use after the erase
(pointing to the next item), so just do:

iter = erase(iter);

Yes. It doesn't change the fact that 'erase(iter++)' is a valid way
to do it, though.

Cool! Thanks, Victor.
-Howard