Re: Containers other than vector - any use?

=?ISO-8859-1?Q?Marcel_M=FCller?= <>
Sun, 22 Aug 2010 01:47:15 +0200
Stephen Howe wrote:


I sometimes wonder about how often containers other than vector are used.

I find that for list/set/map, the overhead of a memory allocation per node is _SO_ dominant, that a sorted vector is frequently
faster setting up and looking up items (and assuming reserve is used).

Well, it depends. Speed is one issue. If you can deal with iterator
invalidation and copy construction of your objects, vector might be
fine. If not, then you have no much choice.
E.g. multi-threaded applications often have their own requirements if
you do not want to serialize all the time.

In general I prefer intrusive containers over std::list and std::set. If
the container interacts with a mandatory base class of the element type,
then there is no additional allocation at all.

And to avoid copy construction I frequently use vectors of smart
pointers. Of course, to prevent additional memory allocations they have
to be intrusive too.

At this point I scratch my head and wonder under what circumstances list/set/map beat vector.
It seems that the more simple the item vector has to manage the size threshold where list/set/map beat vector has to be
something huge. And it seems the only circumstances where vector is poor is where the container is constantly changing during
the lifetime of a program running so that vector's insert and erase are slow due to the sheer number of items.

Yes, vector easily ends up with O(n?) if you have constantly changing data.


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