How to use QTextStream to replace std::ostringstream

[edmhourigan]

I have the following code that I am trying to add a double number to a QLabel that must have the following format MMM.NN , this a number less than 100.0 should have a leading 0

double  _Heading = 35.5;
 
        QString _TextForDisplay;
        QTextStream _Stream(&_TextForDisplay);
        _Stream.setRealNumberNotation(QTextStream::FixedNotation);
        _Stream.setRealNumberPrecision(2);
        _Stream.setFieldAlignment(QTextStream::AlignRight);
        _Stream.setPadChar('0');
 
        _Stream << "HDG: " << QTextStream::ForcePoint << _Heading;
 
        QString _qs = *(lcStream.string());
        std::cout << "_Stream: " << _qs.toUtf8().constData() << std::endl;

double  _Heading = 35.5;

        QString _TextForDisplay;
        QTextStream _Stream(&_TextForDisplay);
        _Stream.setRealNumberNotation(QTextStream::FixedNotation);
        _Stream.setRealNumberPrecision(2);
        _Stream.setFieldAlignment(QTextStream::AlignRight);
        _Stream.setPadChar('0');

        _Stream << "HDG: " << QTextStream::ForcePoint << _Heading;
        
        QString _qs = *(lcStream.string());
        std::cout << "_Stream: " << _qs.toUtf8().constData() << std::endl;

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But I get

"_Stream : 235.50" not "035.50".

??? Where is the leading "2" coming from???

>>

Note that using std:stringstream produces the expected results:

std::ostringstream _TextStream;
        _TextStream  << "HDG: " << std::dec << std::fixed << std::setprecision(2) << _Heading;
        std::cout << lcTextStream.str() << std::endl;

std::ostringstream _TextStream;
        _TextStream  << "HDG: " << std::dec << std::fixed << std::setprecision(2) << _Heading;
        std::cout << lcTextStream.str() << std::endl;

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"035.50"

Thanks.

[d_stranz]

In line 12, you are retrieving the contents of a variable named "lcStream", which is not the same variable as "_Stream".

[edmhourigan]

That's simply typo on line 12. Thanks.

---

Added after 5 minutes:

Corrected:
--------------

double  _Heading = 35.5;
 
        QString _TextForDisplay;
        QTextStream _Stream(&_TextForDisplay);
        _Stream.setRealNumberNotation(QTextStream::FixedNotation);
        _Stream.setRealNumberPrecision(2);
        _Stream.setFieldAlignment(QTextStream::AlignRight);
        _Stream.setPadChar('0');
 
        _Stream << "HDG: " << QTextStream::ForcePoint << _Heading;
 
        QString _qs = *(_Stream.string());
        std::cout << "_Stream: " << _qs.toUtf8().constData() << std::endl;

double  _Heading = 35.5;
 
        QString _TextForDisplay;
        QTextStream _Stream(&_TextForDisplay);
        _Stream.setRealNumberNotation(QTextStream::FixedNotation);
        _Stream.setRealNumberPrecision(2);
        _Stream.setFieldAlignment(QTextStream::AlignRight);
        _Stream.setPadChar('0');
 
        _Stream << "HDG: " << QTextStream::ForcePoint << _Heading;
 
        QString _qs = *(_Stream.string());
        std::cout << "_Stream: " << _qs.toUtf8().constData() << std::endl;

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Is the '2' prefix coming from the call on line 6?

_Stream.setRealNumberPrecision(2);

_Stream.setRealNumberPrecision(2);

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If so, that seems like a bug in QTextStream, right?

---

Added after 14 minutes:

The problem was caused by adding this:
'<< QTextStream::ForcePoint'

ForcePoint operator forces comma separators, not decimal point (poorly named operator, IMHO).


Changing to

_Stream << "HDG: " << _Heading;

_Stream << "HDG: " << _Heading;

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Fixes the leading '2' digit.

>>> IS THIS A BUG in QTextStream ??? <<<

[ChristianEhrlicher]

Why should this be a bug? Out tell QTextStream to output 'QTextStream::ForcePoint' which is 2. What you want is QTextStream::forcePoint().