Converting Qbyte array to array and to double

[dziko147]

Hello , I get some data from a CAN Bus . So my data is some float and some double .

What I did is :

float myData;
double myDatadouble;

                   QDataStream stream(data);
                    qDebug() << data.size() << " Data Data&size" ;
                   
                    if (data.size()== 5){
                       quint8 byte;
                        stream >> byte; // skip first byte
              stream.setFloatingPointPrecision(QDataStream::SinglePrecision);
                        stream >> myData; // read data
                        qDebug()  << "this is data"<< myData ;
                        QString DatatoString =QString::number(myData);
                        Outputs[i]=DatatoString;
                    qDebug() << "In outputs data" << Outputs[i];
                    }
else {

                   quint8 byte;
                    stream >> byte; // skip first byte
                        stream.setFloatingPointPrecision(QDataStream::DoublePrecision);
                     stream >> myDatadouble; // read data
                    qDebug()  << "this is data"<< myDatadouble;
                    QString DatatoString =QString::number(myDatadouble);
                    Outputs[i]=DatatoString;
                    qDebug() << "In outputs data" << Outputs[i];
                    }              
                   

I get only float converted , the double is usually "0" .

thankyou

[artwaw]

@dziko147 in the else part of the case you do QString::number on the float instead of the double?

Plus, using QString::number you can control precision on the double too https://doc.qt.io/qt-5/qstring.html#number-6

[dziko147]

@artwaw thanks for your reply . Ok I will remove the Qstring .

Also I get unreadable data like " 3.13891e-43 " for a array "0xff000000e0" .

I use a online converter and give the same value .

But there is a way to make it readable .

thank you

[artwaw]

@dziko147
again: in the "else" part you have

qDebug()  << "this is data"<< myDatadouble;
QString DatatoString =QString::number(myData);

where I think you should have

qDebug()  << "this is data"<< myDatadouble;
QString DatatoString =QString::number(myDatadouble);

since you do not even set myData in that part. Hence your string contains rubbish, you don't even initialise the variable.

[dziko147]

@artwaw yes in my code I have

qDebug()  << "this is data"<< myDatadouble;
QString DatatoString =QString::number(myDatadouble);

just when i copying it i I was mistaken .

I update my topic :)

[CP71]

@dziko147
Hi,
you have checked only if (data.size()== 5) in first if,
Did you check in else that the data size is correct?
I think no

[dziko147]

@CP71 yes it return a size :8 byte

[CP71]

@dziko147
8! so doesn't you have a one spare byte in else as in float case?

[dziko147]

@CP71 said in Converting Qbyte array to array and to double:

8! so doesn't you have a one spare byte in else as in float case?

no I usually get frame started with FF .

I mean than in the case of a float I get "FF + 4Byte data"

In the case of a Double I get "FF +7Byte data "

and here I skip the first byte

                   quint8 byte;
                    stream >> byte; // skip first byte

[CP71]

@dziko147 said in Converting Qbyte array to array and to double:

In the case of a Double I get "FF +7Byte data "

Sorry, but in double case I think you'd send 0xFF+8bytes, anyway I think your application tries read a double at 8 bytes

[dziko147]

@CP71 you are right :D

[dziko147]

@CP71 now how can make it readable .
For example I get " 3.13891e-43 " for a array "0xff000000e0" .
please

[CP71]

@dziko147
It is wrong!

https://www.binaryconvert.com/convert_double.html

As last time, I must go.
Sorry, bye

[dziko147]

@CP71 as u like bro good bye