[Qt5-feedback] Real 64 Bit support ?

[Andre Somers]

Op Di, 17 mei, 2011 10:11 am, schreef Stephen Bryant:
> On 17/05/2011 09:13, Thiago Macieira wrote:
>> Indeed. That's also the reason why we use ints: if they are used for
>> everything, there are no warnings about mixing signedness or losing
>> precision
>> due to casting to a smaller type.
>
> Only until you have to pass the size of something to/from some other
> interface.
>
> All you're doing is moving the hurdle!  I have to write extra code to do
> bounds checking because of the signed integer, and because of the loss
> of precision.
>
> It would be better to use unsigned values for sizes of things like
> everything else does.  No warnings then either.
I agree there, though there are things to considder. Like, what would you
return from a method like QList::indexOf()? Currently, you get a -1 if
your search did not return any results. But if you change this to an
unsigned integer, what would you return? Perhaps reserve its maximum value
to be the invalid one (and thus making the address space 1 shorter,
instead of dividing it by two). In any case, this would require lots of
code changes in code currently out there. The goal of Qt5 was that it
would stay largely code compatible...

> That said, I'd much prefer ssize_t to the current int.  The 2GB limit on
> 64bit systems would disappear, without impacting 32bit systems.
Then we are back with data exchange issues, are we not? How would a 32 bit
Qt application deal with a data file that contains a list of 2^32 + x
elements? Or that requires an address space larger than 2^32?

André