QT Reading binary file and then convert it to QString

Question

I saved the QString in the file like this:

QString str="blabla";
QByteArray _forWrite=QByteArray::fromHex(str.toLatin1());
f.write(_forWrite); // f is the file that is opened for writing.

Then when I read the file I use QFile::readAll() to take the QByteArray but I don't know how to convert it to QString.

I tried to use the constructor that uses QByteArray but It didn't work out. I tried also with QByteArray::data() but same result. What I do wrong ?

What do you mean "didn't work out"? Compilation error? Runtime error? Runtime OK but garbled data? — david
– david, Commented Oct 1, 2014 at 16:05
Why are you using fromHex on a string that is not hexadecimal? :-/ That is invalid input and not checked, so it won't do what you think. — HostileFork says dont trust SE
– HostileFork says dont trust SE, Commented Oct 1, 2014 at 16:06

Max Go · Accepted Answer · 2014-10-01 16:47:38Z

2

It's not clear why you are calling QByteArray::fromHex at all. toLatin1() already return you QByteArray where each symbol encoded with one byte.

[UPDATE]

You should NOT call QByteArray::fromHex at all, because:

invalid characters in the input are skipped

And invalid characters are characters that are not the numbers 0-9 and the letters a-f

edited Oct 1, 2014 at 16:47

answered Oct 1, 2014 at 15:56

Max Go

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3 Comments

HostileFork says dont trust SE Over a year ago

The string is definitely blabla with lowercase L, as in "blah blah", not "b one a b one a". One shouldn't be calling "fromHex" with that as input. So there's definitely a misunderstanding here.

Max Go Over a year ago

Yes, I just updated the answer with the reason why calling of toHex() doesn't work.

chnging Over a year ago

Yes that was it. I used toHex because I saw an example that used it didn't realise that toLatin1() returns QByteArray. Thanks!

cobalt · Accepted Answer · 2014-10-01 16:15:27Z

1

You can use QDataStream

#include <QApplication>

#include <QDataStream>
#include <QByteArray>
#include <QFile>

int main(int argc, char *argv[])
{
    QApplication app(argc, argv);

        QString strToWrite = "blabla";
        QFile fileToWrite("file.bin");
        QDataStream dataStreamWriter(&fileToWrite);
        fileToWrite.open(QIODevice::WriteOnly);
        dataStreamWriter << strToWrite;
        fileToWrite.close();

        QString strToRead = "";
        QFile fileToRead("file.bin");
        QDataStream dataStreamReader(&fileToRead);
        fileToRead.open(QIODevice::ReadOnly);
        dataStreamReader >> strToRead;
        fileToRead.close();

        qDebug() << strToRead;

    return app.exec();
}

Output : "blabla"

answered Oct 1, 2014 at 16:15

cobalt

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2 Comments

chnging Over a year ago

Thank you but I wanted without QDataStream :)

cobalt Over a year ago

QString s = "blabla"; QByteArray ba = s.toUtf8(); QString s2 = QString::fromUtf8(ba); OR QByteArray ba = s.toLatin1(); QString s2 = QString::fromLatin1(ba); Depends on the character set you will use.

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