How to separate 3 bytes 3 bytes of QStringList
-
@J-Hilk tnx , I need a QList<double>
So I change it to :auto hexastr2double = [](const QString &str, int byteCount)->QList<double>{ QList<double> l; for(int i(0),j(str.size()); i < j; i+=byteCount) l.append(str.mid(i,6).toInt(nullptr, 16)); return l; }; for(const QString & str : fields){ qDebug()<< hexastr2double(str,6);But the output is round, for example the FFD789 is equal by 16766857
And with this code I get 1.67669e+07 =16766900
How to prevent number rounding?@isan
What do you mean by " prevent number rounding"? You are storingints intodoubles. So first there may not be an exactdoublerepresentation of eachintvalue, and second you seem to be commenting on the display output format ofqDebug() << doubleValue, which will use the default general format, you have to specify a specific format of you don't want that.A separate issue is why you would want to take a hex-
int-value and store it into adoublein any case, you are liable to lose accuracy at least for some values, doesn't seem like a good idea.... -
@J-Hilk tnx , I need a QList<double>
So I change it to :auto hexastr2double = [](const QString &str, int byteCount)->QList<double>{ QList<double> l; for(int i(0),j(str.size()); i < j; i+=byteCount) l.append(str.mid(i,6).toInt(nullptr, 16)); return l; }; for(const QString & str : fields){ qDebug()<< hexastr2double(str,6);But the output is round, for example the FFD789 is equal by 16766857
And with this code I get 1.67669e+07 =16766900
How to prevent number rounding?@isan said in How to separate 3 bytes 3 bytes of QStringList:
And with this code I get 1.67669e+07 =16766900
Which is absolute correct.
-
@J-Hilk tnx , I need a QList<double>
So I change it to :auto hexastr2double = [](const QString &str, int byteCount)->QList<double>{ QList<double> l; for(int i(0),j(str.size()); i < j; i+=byteCount) l.append(str.mid(i,6).toInt(nullptr, 16)); return l; }; for(const QString & str : fields){ qDebug()<< hexastr2double(str,6);But the output is round, for example the FFD789 is equal by 16766857
And with this code I get 1.67669e+07 =16766900
How to prevent number rounding?@isan said in How to separate 3 bytes 3 bytes of QStringList:
How to prevent number rounding?
Use
intorint64_t. Don't usedouble. -
@isan said in How to separate 3 bytes 3 bytes of QStringList:
And with this code I get 1.67669e+07 =16766900
Which is absolute correct.
-
@isan said in How to separate 3 bytes 3 bytes of QStringList:
How to prevent number rounding?
Use
intorint64_t. Don't usedouble. -
@isan
What do you mean by " prevent number rounding"? You are storingints intodoubles. So first there may not be an exactdoublerepresentation of eachintvalue, and second you seem to be commenting on the display output format ofqDebug() << doubleValue, which will use the default general format, you have to specify a specific format of you don't want that.A separate issue is why you would want to take a hex-
int-value and store it into adoublein any case, you are liable to lose accuracy at least for some values, doesn't seem like a good idea.... -
@Christian-Ehrlicher yes but rounded
@isan said in How to separate 3 bytes 3 bytes of QStringList:
yes but rounded
It's just a debug output. Simply format the output correctly - C basics
-
@isan said in How to separate 3 bytes 3 bytes of QStringList:
I need QList<double>
Can you explain why?
Your hex strings represent integers, not floating-point numbers. I can't see why you need
QList<double>.I get 1.67669e+07 =16766900
@Christian-Ehrlicher is right. The debug output is displaying 16766857 to 6 significant digits. It is not rounding your value; the value is still 16766857.
You can see it by converting your value back to an integer:
qDebug() << int( hexastr2double(str, 6) ); // Shows 16766857 -
@isan said in How to separate 3 bytes 3 bytes of QStringList:
@JonB can convert QList<int> to QList<double>?
A
QListis just a list, if you can convert oneintto adoubleyou can convert a list ofints to a list ofdoubles.You still haven't said what it is you want
doubles for. Given that the input is hex representation of integers, one would have thought you would want to deal with them asints. Without knowing your usage it's hard to be sure, but my inclination would be to convert these to a list ofints where you do not lose any precision. If you then want to use those number asdoubles for some later purpose, convert the numbers to doubles at the time you need to use them as such rather than at the point you read them in.
