Re: [Boost-users] Efficiacy of std::vector

From: Janos Vegh (vegh.janos_at_[hidden])
Date: 2006-08-26 15:54:55

On 8/26/06, me22 <me22.ca_at_[hidden]> wrote:
>
>
> main has to return int; Your code isn't legal C++.  Also, it seems
> like you end up using memory in the vector after only reserving it,
> not resizing it.

Yes, a forgotten  int, my mistake.
After reserving the  memory, I guess I can  write the memory  locations.
I think neither of the above affects the subject.

Your empty cycle time makes it obvious you're not even doing the most
> rudimentary of optimizations.

My goal was to measure the time of the empty processing,
in order to estimate the time of the net calculation,
rather than to find out that for no operation I need no time.

Here's what I get in g++ (g++ (GCC) 4.1.1 (Gentoo 4.1.1)) after making
> a few changes while using -O3 -DNDEBUG as arguments to the compiler
> (though -DNDEBUG didn't make any signifigant difference):
>
> Empty cycle
> real    0m0.003s
> user    0m0.000s
> sys     0m0.000s
>
> STL=1, SIMPLE=1, size=1000
> real    0m1.357s
> user    0m1.168s
> sys     0m0.008s
>
> STL=1, size=1000
> real    0m1.337s
> user    0m1.172s
> sys     0m0.016s
>
> STL=1, ITERATOR=1, size=1000
> real    0m1.315s
> user    0m1.172s
> sys     0m0.012s
>
> STL=1, AT=1, size=1000
> real    0m1.357s
> user    0m1.176s
> sys     0m0.004s
>
> I really don't see an issue here.
>
> I neither, except that it looks like that in the case of AT checking the
lower and upper
limits of the index needs no extra time(??).

Otherwise, on my system
$ g++ -oeffic2.exe effic2.cpp
$ time ./effic2.exe
STL=1, SIMPLE=1, ITERATOR=0, AT=0, size=1000
real    0m4.775s
user    0m4.476s
sys     0m0.080s

$ g++ -o3 -oeffic2.exe effic2.cpp
$ time ./effic2.exe
STL=1, SIMPLE=1, ITERATOR=0, AT=0, size=1000
real    0m4.749s
user    0m4.496s
sys     0m0.060s

and

$ g++ -o3 -oeffic2.exe effic2.cpp
$ time ./effic2.exe
STL=1, SIMPLE=0, ITERATOR=0, AT=0, size=1000
real    0m33.413s
user    0m32.076s
sys     0m0.100s

$ g++ -oeffic2.exe effic2.cpp
$ time ./effic2.exe
STL=1, SIMPLE=0, ITERATOR=0, AT=0, size=1000
real    0m34.554s
user    0m33.668s
sys     0m0.060s

and

$ g++ -oeffic2.exe effic2.cpp
$ time ./effic2.exe
STL=1, SIMPLE=0, ITERATOR=0, AT=1, size=1000
real    1m26.753s
user    1m24.301s
sys     0m0.080s

$ g++ -o3 -oeffic2.exe effic2.cpp
$ time ./effic2.exe
STL=1, SIMPLE=0, ITERATOR=0, AT=1, size=1000
real    1m29.311s
user    1m27.035s
sys     0m0.050s

After that you were so kind to run my  test on your Linux,
maybe I need to ask MingW people about this  problem.

Anyhow, thanks for replying and sorry for bothering the list with my problem

Janos