Re: STL vector

Joshua Maurice <>
Thu, 17 Nov 2011 15:19:23 -0800 (PST)
On Nov 17, 7:45 am, "Peter Liedermann" <> wrote:

On Wed, 16 Nov 2011 15:02:44 +0100, Leigh Johnston <> wrot=


On 15/11/2011 19:50, Peter Liedermann wrote:
If you are going to allocate the Jumbo objects separately for use in
vector<Jumbo*> then you might as well just use std::set<Jumbo>; std::se=


will keep the items sorted.

Thank you for the suggestion. However, I am not going to use set becau=


I occasionally have to re-sort.

In my case, this resort would be quite
intense, that is, almost everything is repositioned each time. This is
definitely not a hot spot in the algorithm, but I do not want to swear
that it occurs at most so and so often. For this reason, I want to avo=


tree-like structures, which an STL set essentially is.

But BTW, this takes us back to a variation the original question: Would
you, given the use of a set, really use std::set<Jumbo> or std::set<Jumbo
*> instead and does it make a difference
(that is, does replacing "vector" by "set" in the original question make =



It depends on a lot of things. You really haven't given me enough
information to determine the answer.

If you question is "Given a pre-existing list of stuff that's
expensive to copy, how do I figure out what is the sorted sequence of
those objects?", then the answer is pretty straightforward. Define the
following class:
    struct JumboPointerSortRule
        bool operator() (Jumbo* x, Jumbo* y) const { return *x < *y; }
Then create a std::set<Jumbo*, JumboPointerSortRule>, and insert a
pointer of each element in the unsorted sequence to this set. Voila,
you now have a view on your original objects, where the view is in
sorted order, all with a minimum of fuss and CPU/memory usage. Unless
a profiler tells you differently, or you know up front some very
specific facts (you would know what those facts are if you knew them),
then don't worry about it and do it this way.

The answer may change if you have C++11. I'm currently too ignorant of
such things to comment.

If your question is more of a architecture question, then you haven't
given me enough information to work through how I'd do it.

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