On Tuesday 19 January 2016 11:15:43 Milian Wolff wrote:
> On Dienstag, 19. Januar 2016 11:51:42 CET Marc Mutz wrote:
> > I missed one:
> >
> > On Monday 18 January 2016 23:43:37 Marc Mutz wrote:
> > > #include <QVector>
> > > #include <string>
> > >
> > > int main() {
> > >
> > > QVector<QByteArray> l;
> > > int oldC = l.capacity();
> > > for (int i = 0; i < 10000000; ++i) {
> > >
> > > char buf[std::numeric_limits<int>::digits + 1];
> > > sprintf(buf, "%d", i);
> > > l.push_back(buf);
> > > int newC = l.capacity();
> > > if (newC != oldC)
> > >
> > > qDebug("%d", newC);
> > >
> > > oldC = newC;
> > >
> > > }
> > >
> > > }
> > >
> > > $ time ./test
> > > <snip>
> > > real 0m1.769s
> > > user 0m1.572s
> > > sys 0m0.192s
> >
> > Same with std::vector<QByteArray>:
> >
> > real 0m1.776s
> > user 0m1.616s
> > sys 0m0.156s
> >
> > > best of three runs, core i7-2720QM, GCC 5.3
> >
> > Ditto.
> >
> > So... is realloc actually the optimisation everyone (incl. me) expected
> > it to be?
>
> Did you run it through a profiler? Where is the time actually spent?
No. It's not the IO, though. Removing the qDebug() and capacity tracking, it
performs the same, within error margins.
--
Marc Mutz <marc.m...@kdab.com> | Senior Software Engineer
KDAB (Deutschland) GmbH & Co.KG, a KDAB Group Company
Tel: +49-30-521325470
KDAB - The Qt Experts
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