reading 4-bytes integer from binary file

[maka]

Hello, people.

Нelp me please with subject.
Im a beginner in QT. It looks like QT has only 8/16/32/64-bytes integer. Is there is a way to read 4-bytes integer from binary file in QT?

Thank you!

[Ginsengelf]

Those numbers are bits, not bytes.

Ginsengelf

[faldzip]

And 8 bits is 1 byte so you are looking for 32-bit integer which is exactly 4-byte integer. In Qt it's qint32.

[maka]

Oh! Im just an idiot!
Thank you for illumination.

[maka]

Ok. Illumination is good but the code still doesnt work.

QFile Source_file;
    Source_file.setFileName("D:/Dela/QTtest/Begin.rg2");
    if (Source_file.open(QIODevice::ReadOnly)) {
        QDataStream data (&Source_file);
//        data.setByteOrder(data.LittleEndian);
        qint32 intb;
        data>>intb;
        qDebug()<<intb;
    }
    Source_file.close();

QFile Source_file;
    Source_file.setFileName("D:/Dela/QTtest/Begin.rg2");
    if (Source_file.open(QIODevice::ReadOnly)) {
        QDataStream data (&Source_file);
//        data.setByteOrder(data.LittleEndian);
        qint32 intb;
        data>>intb;
        qDebug()<<intb;
    }
    Source_file.close();

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I have a value of intb different from that was saved in file. I tried both LittleEndian and BigEndian.
The file was made in Delphi. It reads well in Delphi and in Java.

What the problem may be in?

Thank you.

[wysota]

What the problem may be in?

The problem is in using QDataStream. It's a serialization mechanism that stores (and expects) some additional data in the stream. If you just want to read 4 bytes from the file, use QIODevice::read on the QFile object and cast the data to a type of your choice.

[maka]

The problem is in using QDataStream. It's a serialization mechanism that stores (and expects) some additional data in the stream. If you just want to read 4 bytes from the file, use QIODevice::read on the QFile object and cast the data to a type of your choice.

Thanks for reply!

Now Im trying to do this:

QFile Source_file;
    Source_file.setFileName("D:/Dela/QTtest/Begin.rg2");
 
    if (Source_file.open(QIODevice::ReadOnly)) {
        qint32 intb;
        QByteArray bar;
        bar = Source_file.read(4);
        bool ok;
        intb = bar.toInt(&ok,0);
        qDebug()<<intb;
 
    }
    Source_file.close();

QFile Source_file;
    Source_file.setFileName("D:/Dela/QTtest/Begin.rg2");
  
    if (Source_file.open(QIODevice::ReadOnly)) {
        qint32 intb;
        QByteArray bar;
        bar = Source_file.read(4);
        bool ok;
        intb = bar.toInt(&ok,0);
        qDebug()<<intb;

    }
    Source_file.close();

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Still have wrong result. I suspect becouse of endianity. Is there is a way to fix it avoiding manual changing of bytes order?

[wysota]

toInt() does something completely different. What you need to do is something like this:

QByteArray ba = file.read(4);
qint32 x;
memcpy(&x, ba.constData(), 4);

QByteArray ba = file.read(4);
qint32 x;
memcpy(&x, ba.constData(), 4);

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[maka]

It works.

Thank you very much!