[Interest] 64 bit capable QVector

[Alex Malyushytskyy]

This question appears on the mailing lists since Qt 3 at least .

At one point I was disappointed with having signed int restriction, but
then I decided
that  QT containers are just a convenience classes which are designed to
work with either widgets or data of limited size displayed
by that widgets.

If  guaranteed performance is needed you should use STL anyway.

Regards,
     Alex


On Tue, Sep 3, 2013 at 11:58 AM, Constantin Makshin <cmakshin at gmail.com>wrote:

> Thanks for the explanation, although I still don't appreciate the choice
> (mostly regarding the size, not signedness). :)
>
> On 09/03/2013 10:48 PM, Thiago Macieira wrote:
> > On terça-feira, 3 de setembro de 2013 22:18:39, Constantin Makshin wrote:
> >> Could you please explain (or give a link to an article or something like
> >> that) the reasons Qt developers used to choose signed 32-bit integer for
> >> this purpose?
> >> Signed 32-bit container sizes, i.e. number of elements in a container,
> >> would be acceptable (considering the equation 'n * sizeof(T)' for the
> >> amount of memory consumed by the array alone) but why use them to
> >> calculate and store sizes of allocated memory blocks?
> >
> > For two reasons:
> >
> > 1) it's signed because we need negative values in several places in the
> API:
> > indexOf() returns -1 to indicate a value not found; many of the "from"
> > parameters can take negative values to indicate counting from the end.
> So even
> > if we used 64-bit integers, we'd need the signed version of it. That's
> the
> > POSIX ssize_t or the Qt qintptr.
> >
> > This also avoids sign-change warnings when you implicitly convert
> unsigneds to
> > signed:
> >       -1 + size_t_variable            => warning
> >       size_t_variable - 1             => no warning
> >
> > 2) it's simply "int" to avoid conversion warnings or ugly code related
> to the
> > use of integers larger than int.
> >
> > io/qfilesystemiterator_unix.cpp:
> >         size_t maxPathName = ::pathconf(nativePath.constData(),
> _PC_NAME_MAX);
> >         if (maxPathName == size_t(-1))
> >
> > io/qfsfileengine.cpp:
> >     if (len < 0 || len != qint64(size_t(len))) {
> >
> > io/qiodevice.cpp:
> > qint64 QIODevice::bytesToWrite() const
> > {
> >     return qint64(0);
> > }
> >
> >                     return readSoFar ? readSoFar : qint64(-1);
> >
> >
> >>
> >> On 09/03/2013 08:42 PM, Thiago Macieira wrote:
> >>> On terça-feira, 3 de setembro de 2013 19:33:47, Mehmet İpek wrote:
> >>>> Btw, size
> >>>> limit of QVector is 2^31 in 64 bit platforms too?
> >>>
> >>> Yes. All Qt container classes use a signed int for sizes.
>
>
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>
>
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