std::list::clear()

[scooter]

std::list::clea r() can slow down the performance of a method
considerably if it is called many times a second. I have countered
this problem a little by assigning a fixed size to a list when
instantiated and keeping track of the elements through iterator logic.
This seems a little messy to me though. I'm sure the guys who created
the STL must have a speedier method.

How do you guys clear and reuse a std::list multiple times with as
little slowdown as possible? (where the number of elements to be
inserted each iteration is unknown)

I preferably would like to use lists that have an undetermined size at
runtime.

thanks for any help.

[Attila Feher]

Re: std::list::clea r()

scooter wrote:[color=blue]
> std::list::clea r() can slow down the performance of a method
> considerably if it is called many times a second. I have countered
> this problem a little by assigning a fixed size to a list when
> instantiated and keeping track of the elements through iterator logic.
> This seems a little messy to me though. I'm sure the guys who created
> the STL must have a speedier method.
>
> How do you guys clear and reuse a std::list multiple times with as
> little slowdown as possible? (where the number of elements to be
> inserted each iteration is unknown)
>
> I preferably would like to use lists that have an undetermined size at
> runtime.[/color]

I don't use list if I need to clear it all the time. Then I use something
else, something less "slow to walk".

If I were you I would first test if it is really the list::clear, which is
expensive or your list elements (your classes) are expensive to destroy?

IMO you need something else not a list - or you need to place a reference to
your objects into the list, not a copy. It depends on what is really slow
in your program. A good profiler should tell.

--
Attila aka WW

[jean Davy]

Re: std::list::clea r()

use "resize( 0 )"
but optimizing is a full task

"scooter" <scooter@btopen world.com> a écrit dans le message de
news:r87onvgdtr aq52oemuvqu8t3r ta24b8t61@4ax.c om...[color=blue]
> std::list::clea r() can slow down the performance of a method
> considerably if it is called many times a second. I have countered
> this problem a little by assigning a fixed size to a list when
> instantiated and keeping track of the elements through iterator logic.
> This seems a little messy to me though. I'm sure the guys who created
> the STL must have a speedier method.
>
> How do you guys clear and reuse a std::list multiple times with as
> little slowdown as possible? (where the number of elements to be
> inserted each iteration is unknown)
>
> I preferably would like to use lists that have an undetermined size at
> runtime.
>
> thanks for any help.[/color]

[tom_usenet]

Re: std::list::clea r()

On Thu, 02 Oct 2003 18:19:37 +0530, scooter <scooter@btopen world.com>
wrote:
[color=blue]
>std::list::cle ar() can slow down the performance of a method
>considerably if it is called many times a second. I have countered
>this problem a little by assigning a fixed size to a list when
>instantiated and keeping track of the elements through iterator logic.
>This seems a little messy to me though. I'm sure the guys who created
>the STL must have a speedier method.
>
>How do you guys clear and reuse a std::list multiple times with as
>little slowdown as possible? (where the number of elements to be
>inserted each iteration is unknown)
>
>I preferably would like to use lists that have an undetermined size at
>runtime.[/color]

Using a fixed size object allocator for the list would likely remove
the bottleneck. e.g.

http://www.boost.org/libs/pool/doc/index.html

typedef std::list<Eleme nt, boost::pool_all ocator<Element> >
ElementList_t;

Alternatively, pick a different container like vector or deque, which
have faster clear behaviour.

Tom