[Insight-users] Using c++ stl containers in the transform?

[Luis Ibanez]

Hi Motes,

Please see comments interleaved with your text below.

    Thanks

             Luis


-------------------------------------------
On Thu, Dec 10, 2009 at 12:09 PM, motes motes <mort.motes at gmail.com> wrote:
> On Thu, Dec 10, 2009 at 3:23 PM, Luis Ibanez <luis.ibanez at kitware.com> wrote:
>> Hi Motes,
>>
>> Before we dive into the details of your code....
>>
>> Are you compiling you application for "Release"  ?
>
>
> Yes
>
>> In order to do profiling comparisons, you must
>> start first by making sure that you are using the
>> compiler's optimization.
>>
>>
>> Using STL containers is as efficient as using
>> pointers, as long as you access the elements
>> of the container via STL iterators.
>
> I have not found any documentation that says that doing:
>
> std::vector<std::string> container;
> // Add 100000 strings to container
>
> std::vector<std::string>::iterator it = container.begin()
> while (it != container.end()) {
>  std::string str = *it;
>  // do something with str
>  it++;
> }
>
> is faster than:
>
> int size =  container.size();
> for (int i=0; i< size; i++) {
>  std::string str = container[i];
>  // do something with str
> }
>
>
> I have tried both implementation in my transform and I do not
> experince any difference in performance.
>



Yes, that's exactly what I said in my previous email:

That using STL iteratos is *as fast as* using pointers.
(as long as you compile for Release).



>
>> Do the operations of mapping points involve
>> inserting new elements or removing exising
>> elements from the STL containers in your
>> Transform  ?
>>
>
> I only lookup existing elements and read the contents of those. I do
> not add or delete any elements.
>
>


What method are you using for "looking up" elements in the container ?
and ... what container are you using ? (std::vector ? std::map?).


>
>
>
>>
>>    Please let us know,
>>
>>
>>        Thanks
>>
>>
>>             Luis
>>
>>
>> --------------------------------------------------
>> On Thu, Dec 10, 2009 at 7:09 AM, motes motes <mort.motes at gmail.com> wrote:
>>> I have created a transform (TransformPoint) that iterates a
>>> std::vector base on a lookup in a std::map. I can't get the same
>>> performance compared to running the  BSplineDeformableTransform and I
>>> suspect that its beause I use the stl containers. Typically I only
>>> iterate 10-40 elements in the vector based on a single lookup in the
>>> map (lg n time).
>>>
>>> Does anyone have experiences with the pros and cons of using the stl
>>> containers in per pixel/voxel functions like the TransformPoint in the
>>> BSplineDeformableTransform?
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>>
>