(Qt C++) Write QString to file as Binary

Question

I am working on a project and I need to write (and in the future read) a string (QString) as binary. The string is in HEX format, like this "00010203040506070a0f01" etc...

I got this far through a tutorial on YouTube:

void Output()
{
    QString ye("01020a");
    QFile file("C:\\Users\\Public\\Documents\\Qt_Projects\\myfile.dat";

    if(!file.open(QIODevice::WriteOnly))
    {
        qDebug() << "Could not open file to be written";
        return;
    }

    QDataStream out(&file);
    out.setVersion(QDataStream::Qt_5_0);

    out << ye;

    file.flush();
    file.close();
   }

But when I open "myfile.dat" with a hex editor, the hex values are different, the QString "ye" was written to the text side of things.

00 00 00 0C 00 30 00 31 00 30 00 32 00 30 00 61

Help?

Pavel Strakhov · Accepted Answer · 2013-07-11 21:08:10Z

8

You should convert it before writing.

QByteArray array = QByteArray::fromHex(ye.toLatin1());
file.write(array);

You don't need to use QDataStream since you already have QByteArray and can write it directly.

You can read and convert the data back to hex representation as follows:

QString s = file.readAll().toHex();

edited Jul 11, 2013 at 21:08

answered Jul 11, 2013 at 20:34

Pavel Strakhov

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5 Comments

mrg95 Over a year ago

Worked like a charm :) Thx I need to wait 4 min before accepting

mrg95 Over a year ago

Just wondering, how would I go about reading a file to a QString? I'm assuming a variation of this, but anything I'm missing?

Pavel Strakhov Over a year ago

Do you mean converting it back to hex representation? QString s = file.readAll().toHex();

mrg95 Over a year ago

Perhaps, what is the easiest way to print the string? I'm very new to qt. Im messing with qDebug but I don't know where it displays

mrg95 Over a year ago

Yes it worked :) I foudn the App Output and everything is perfect!

Tushar Gupta - curioustushar · Accepted Answer · 2013-07-12 07:14:05Z

1

in QString each character occupy 2 bytes (Using unicode). You can consult the ascii table to search a character's code value in hex int:

'0': 0x30
'1': 0x31
'a': 0x61

so for the string "01020a" its ascii code sequence is: 00 30 00 31 00 30 00 32 00 30 00 61

"00 00 00 0C": I think it's the type identify for QString.

Sorry for my poor expression, hope it's useful.

edited Jul 12, 2013 at 7:14

Tushar Gupta - curioustushar

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answered Jul 12, 2013 at 6:52

Biao

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Comments

JaeSuk Park · Accepted Answer · 2016-03-09 07:42:37Z

0

Saving QString to QFile;

QString qStr="abc";
qFile.write(qStr.toUtf8().constData());

conversion sequences are here;
   QString => QByteArray => const char* => QFile.write()

[ref class function]

QByteArray QString::toUtf8() const;
const char * QByteArray::constData() const;
qint64 QIODevice::write(const char * data);

edited Mar 9, 2016 at 7:42

answered Mar 9, 2016 at 2:17

JaeSuk Park

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