Write Unicode UTF-8 and UTF-16 data into a QByteArray

Question

I'm developing a protocol for my company using Qt. It is required to query the Window Registry and write the value obtained into a prenegotiated socket. I have read the Registry Data into a QString . I must use 8-bit Unicode characters and for some 16-bit Unicode characters. I am using QByteArray to store all the data before writing to the socket using QTcpSocket::write() . Little Endianness must be followed.

1. How do I get the data from QString into QByteArray in Unicode 8 bit format (specification says character type corresponds to quint8 )?

2. How do I get the data from QString into QByteArray in Unicode 16 bit format (specification says character type corresponds to quint16 )?

3. How can I maintain Little Endianness in all cases?

(I have no experience of dealing with Unicode/variable-byte-encoded data)

Answer 1

Looking in the documentation is a good start.

1. QString::toUtf8()
2. Create a new QByteArray starting with a BOM . Use QString::utf16() to get the ushort values, mask out the top and bottom halves in the endianness you want into the QByteArray.
3. UTF-8 doesn't have/need endianness. The ushort masks needed to put 16-bit values into an 8-bit array for little endianness would be 0x00FF then 0xFF00 .
4. Read The Absolute Minimum Every Software Developer Absolutely, Positively Must Know About Unicode and Character Sets (No Excuses!) at home tonight.

Answer 2

For your question # 2 - How to convert QString to UTF-16 QByteArray, there is a solution with QTextCodec::fromUnicode(), as shown in the following code example:

#include <QCoreApplication>
#include <QTextCodec>
#include <QDebug>

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

    // QString to QByteArray
    // =====================

    QString qstr_test = "test"; // from QString
    qDebug().noquote().nospace() << "qstr_test[" << qstr_test << "]";     // Should see: qstr_test[test]

    QTextCodec * pTextCodec = QTextCodec::codecForName("UTF-16");

    QByteArray qba_test = pTextCodec->fromUnicode(qstr_test); // to UTF-16 QByteArray
    qDebug() << "qba_test[";
    int test_size = qba_test.size();
    for(int i = 0; i < test_size; ++i) { // Should see each UTF-16 encoded character per line like this: ÿþt e s t
        qDebug() << qba_test.at(i);
    }
    qDebug() << "]";

    return a.exec();
}

The above code has been tested using Qt 5.4.