[Development] Weird offseting in QDataStream

[Christian Ehrlicher]

Am 08.11.2013 10:42, schrieb André Somers:
> Christian Ehrlicher schreef op 8-11-2013 10:29:
>> Am 08.11.2013 10:15, schrieb Yves Bailly:
>>> Le 08/11/2013 10:05, Giuseppe D'Angelo a écrit :
>>>> On 8 November 2013 10:01, Yves Bailly<yves.bailly at sescoi.fr>  wrote:
>>>>> As a float is 4 bytes, I would expect the second f.pos() to display "4"... but
>>>>> it displays "8", as if QDataStream had moved 8 bytes ahead instead of just 4.
>>>>> Needless to say, the read float is wrong...
>>>>>
>>>>> Am I missing something here, or is it a bug?
>>>> See QDataStream::setFloatingPointPrecision. The default is double.
>>> That's pretty strange... what if I want to read a float then a double? do I
>>> have to switch between the two each time?
>>> Does this means it's impossible to use code like this:
>>> float f;
>>> double d;
>>> datastream >> f >> d;
>>> ?
>> setFloatingPointPrecision does only change the way the floating point
>> numbers are stored in the data stream, not what you read from it.
>> Also I think you're wrong in what you want to do. You can't read data
>> from a file which was not stored with QDataStream before! See
>> http://qt-project.org/doc/qt-5.0/qtcore/qdatastream.html#details
> That sounds very unlikely. It would mean that you cannot use symetric 
> code for reading and writing data:
>
> //writing
> float f(3.14159);
> double d(2.71828);
> datastream << f << d;
>
> //reading, would not work according to Christian
> float f;
> double d;
> datastream >> f >> d; //would not work according to you
>
> //reading, according to Christian
> float f;
> double df, d;
> datastream >> df >> d;
> f = static_cast<float>(d);
>
> I'm quite sure that you _can_ use the symetric (first) version.
>
You're correct - you understood me wrong. :)

Christian
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