QDomDocument always uses system locale settings while writing double numbers in Linux.

Tetsuzin72

I have tried to write down float and double numbers to xml file. But there is a problem:
float numbers always writing with dot decimal separator and double numbers wtiteing with comma seperator even if programm locale set to QLocale::C.

Thera two variables:
float floatVal = 0.1234f;
double doubleVal = 0.1234;

When I wtite them to QDomDocument the output file looks like this:

<Root doubleVal="0,1234" floatVal="0.1234"/>

This issue only happens in Linux. In Windows everythins is Ok.
Is it a bug?

System locale settings are:

user@paefimov:~$ locale
LANG=en_US.UTF-8
LANGUAGE=en_US
LC_CTYPE="en_US.UTF-8"
LC_NUMERIC=ru_RU.UTF-8
LC_TIME=en_US.UTF-8
LC_COLLATE="en_US.UTF-8"
LC_MONETARY=ru_RU.UTF-8
LC_MESSAGES="en_US.UTF-8"
LC_PAPER=ru_RU.UTF-8
LC_NAME=ru_RU.UTF-8
LC_ADDRESS=ru_RU.UTF-8
LC_TELEPHONE=ru_RU.UTF-8
LC_MEASUREMENT=ru_RU.UTF-8
LC_IDENTIFICATION=ru_RU.UTF-8
LC_ALL=

#include <QCoreApplication>

#include <QDomDocument>
#include <QFile>
#include <QTextStream>
#include <QDebug>

int main(int argc, char* argv[])
{
    QCoreApplication a(argc, argv);

    QLocale locale(QLocale::C);

    QLocale::setDefault(locale);

    QFile xmlFile("data.xml");
    xmlFile.open(QIODevice::WriteOnly);

    QDomDocument xmlWriter;

    QDomElement rootNode = xmlWriter.createElement("Root");
    xmlWriter.appendChild(rootNode);

    float floatVal = 0.1234f;
    double doubleVal = 0.1234;

    rootNode.setAttribute("DecimalPoint", locale.decimalPoint());
    rootNode.setAttribute("floatVal", floatVal);
    rootNode.setAttribute("doubleVal", doubleVal);

    xmlFile.write(xmlWriter.toByteArray());
    xmlFile.close();

    QString textData = xmlWriter.toString();

    QDomDocument xmlReader;
    xmlReader.setContent(textData);

    QDomElement root = xmlReader.documentElement();
    double fVal = root.attribute("floatVal").toDouble();
    double dVal = root.attribute("doubleVal").toDouble();

    qDebug() << fVal << dVal;

    return a.exec();
}

JonB

@Tetsuzin72
If you do not get a better reply here, I would say it does look like a bug, and yes should be reported to Qt bug system. For this you need to tell us & them just which version of Qt you are using for this behaviour?

Christian Ehrlicher

The documentation is wrong here (and so the implementation):

The number is formatted according to the current locale.

For double this is true, for float internally QString::setNum() is called which explicitly states:

The formatting always uses QLocale::C, i.e., English/UnitedStates.

Now the question is - what does xml need. I would guess QLocale::C.

Please open a bug report, refer to this thread and assign it to me. :)

Christian Ehrlicher

And QDomElement::setAttributeNS(..., float) doesn't exist at all... hmm

Tetsuzin72

Helo! I'v opened a bug report:
QTBUG-80068

aha_1980

sometimes strange thing happen.

Someone decided to even translate printf output, which affects programs like gdb itself printing and readin float numbers. you can workaround this with LC_NUMERIC, but that influences your own program too... A mess!

Regards