While I don't want to say that STL is a bad thing (it's not bad at all), the fact that its allocators (and, as a consequence, everything that uses them) are by design very friendly to memory fragmentation (the "allocate new block -> copy data -> free old block" makes it completely impossible even to shrink a block of memory in-place) makes me a bit sad...
On 09/04/2013 03:21 AM, Alex Malyushytskyy wrote: > Forgot to add, > > I am not trying to offend performance or any other aspect of Qt container. > Personally all my code related to displaying data use them. > > I just believe it is not replacement for STL. > > Regards, Alex > > > > On Tue, Sep 3, 2013 at 4:16 PM, Alex Malyushytskyy <alexmal...@gmail.com > <mailto:alexmal...@gmail.com>> wrote: > > >> STL is first of all an interface and there are various > implementations, hence your remark about performances does not make > sense. > > It does. All implementations of STL I ever used are clear about > their effectiveness, associated types and complexity guarantees. > > >> Qt containers are far more than "just convenience" classes > > They are designed to work within Qt only. > As far as I understand they never meant to be one of implementation > or replacement of STL, thus it is not provided if not counted rare > exceptions . > Thus these are 'convenience' classes which provide sufficient in > terms of data size and performance support of tasks common for Qt. > > I would add that Qt containers are designed to work with Qt widgets > and carry the same limitations. > And until it is impossible for example to fill QCombobox the number > of items which exceeds capabilities of Qt container, it does not > make sense to change the containers. > > But I disagree with "99.9% of Qt programmers don't need 64 bit > containers." statement. > It might be true for mobile devices , but it is false even for home > desktops. > > Even if simply counting % of software which have to handle data > exceeding 32 bit limit on the home personal computer you will get > higher %. > Rising of interest in distributed computing including visualization > probably does not meant to solve problems with low memory requirements. > > I would expect most of the scientific programs need to support 64 > bit containers even though sometimes they might need that support > occasionally . > > Alex > > > > On Tue, Sep 3, 2013 at 2:55 PM, Philippe <philw...@gmail.com > <mailto:philw...@gmail.com>> wrote: > > I could easily guess 99.9% of Qt programmers don't need 64 bit > containers... Qt containers are far more than "just convenience" > classes. > > STL is first of all an interface and there are various > implementations, hence your remark about performances does not > make sense. > > Philippe > > On Tue, 3 Sep 2013 14:44:58 -0700 > Alex Malyushytskyy <alexmal...@gmail.com > <mailto:alexmal...@gmail.com>> wrote: > > > 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 > <cmaks...@gmail.com <mailto:cmaks...@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 Ipek 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.
signature.asc
Description: OpenPGP digital signature
_______________________________________________ Interest mailing list Interest@qt-project.org http://lists.qt-project.org/mailman/listinfo/interest
