[Interest] 64 bit capable QVector

[Constantin Makshin]

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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