Re: Amazing Performance Difference between vec[] and iterators

[Mark]

thoth39 wrote:
> Ulrich Lauther wrote:
>
> > Paulo Matos <pocmatos@gmail.com> wrote:
> > : Hi all,
> >
> > : I've wanted to know if there was any performance difference between
> > : using:
> > : for(vector<int>::const_iterator it = v.begin(); it != v.end(); ++it)
> >
> > : and
> >
> > : for(unsigned int k = 0; k < v.size(); ++k)
> >
> > Try
> >
> > unsigned int size = v.size();
> > for (unsigned int k = 0; k < size; ++k)
> >
> > in your version size() is evaluated size times
>
>
> Likewise, instead of
>
> for(vector<int>::const_iterator it = v.begin(); it != v.end(); ++it)
>
> try
>
> for(vector<int>::const_iterator it = v.begin(), end = v.end(); it !=
> end; ++it)
>
> to avoid calling v.end() every time.

Aren't compilers smart enough yet to in effect do that if it sees there's
nothing done inside the loop that would change the vector's size?
That seems like something an optimizer should do.