QString to ASCII QByteArray

kshegunov

Hello,
I need to convert a QString data into an ASCII containing QByteArray (I need to have the ^Z character in it). In Qt 4 there was the QString::toAscii method however it was deprecated in favor of QString::toLatin1. There's note put in the documentation about said method, though:

The returned byte array is undefined if the string contains non-Latin1 characters. Those characters may be suppressed or replaced with a question mark.

As far as I know, the latin1 charset (ISO/IEC 8859-1:1998) doesn't specify anything about the codes for non-printable characters under 0x20. So my question boils down to:
Can I use QString::toLatin1, and will my ^Z character be preserved?

Kind regards.

Paul Colby

@kshegunov said:

I need to convert a QString data into an ASCII containing QByteArray (I need to have the ^Z character in it).

Just an idea: why not use QString::toUtf8? Since all UTF-8 characters less than 128 are the same as ASCII, then that should give you your ^Z character correctly.

If your string happens to contain characters greater than 127, then what would you expect to get in the QByteArray? Latin-1? UTF-8? Something else? Where is the QByteArray going / being used?

Depending on your answers, its possible that what you really want is one or more of:

QString::toLocal8Bit
QString::toUtf8
not use QString at all, but start and end with QByteArray (if you're dealing with binary data).

In Qt 4 there was the QString::toAscii method however it was deprecated in favor of QString::toLatin1.

For what its worth, here's what source code for QString::toAscii looked like in Qt4:

QByteArray QString::toAscii() const
{
#ifndef QT_NO_TEXTCODEC
    if (codecForCStrings)
        return codecForCStrings->fromUnicode(*this);
#endif // QT_NO_TEXTCODEC
    return toLatin1();
}

So you were probably getting either equivalent behaviour to QString::toLocal8Bit, or QString::toLatin1? No wonder the function was deprecated... its behaviour is pretty ambiguous, and host-configuration dependant (when you look into the default text codec).

Cheers.

kshegunov

@Paul-Colby
That was fast! ;)

Just an idea: why not use QString::toUtf8? Since all UTF-8 characters less than 128 are the same as ASCII, then that should give you your ^Z character correctly.

Works for me, I don't know why I didn't think of that in the first place ... :D

If your string happens to contain characters greater than 127

It doesn't.

Something else? Where is the QByteArray going / being used?

It's going through the serial port, but I am dealing with text data. (QSerialPort expects a QByteArray, and the device accepts ASCII data, possibly other charsets but I don't want to deal with them ...)

No wonder the function was deprecated... its behaviour is pretty ambiguous, and host-configuration dependant

QString::toLocal8Bit is host-configuration dependent as well, but as I said I'm dealing with latin text only + a few non-printables (under 0x20).

Thanks for the suggestion(s)! I'll stick to utf8 and everything should be just fine.
Kind regards.

andr

If .toAscii() worked for you before, you can savely use .toLatin1(), too, and ^Z will be preserved.