Reading a binary file with QT

[YuriyRusinov]

I have to read binary file via Qt. In console application I make

FILE * fid5 = fopen ("./test_data/source.rgg", "rb");
 
    ...
    for (int i=1; i<=na; i++)
    {
        fread (st+i-1, sizeof (unsigned long), nd2, fid5);
        ...
    }

FILE * fid5 = fopen ("./test_data/source.rgg", "rb");

    ...
    for (int i=1; i<=na; i++)
    {
        fread (st+i-1, sizeof (unsigned long), nd2, fid5);
        ...
    }

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and all work fine. In Qt application I try

QString fileName = QFileDialog::getOpenFileName (this, tr("Select
source file"), QDir::currentPath(), tr("All files (*)"));
    if (fileName.isEmpty())
        return;
    ...
 
    QFile * fData = new QFile (fileName);
 
    for (int i=1; i<=na; i++)
    {
        char * colData = new char [nd2*sizeof (unsigned long)];
        qint64 colLength = fData->readLine (colData, nd2*sizeof
(unsigned long));
        if (colLength < 0)
        {
            qDebug () << __PRETTY_FUNCTION__ << QString ("Read error");
            continue;
        }
        QByteArray buff (colData);
        delete [] colData;
        //qDebug () << __PRETTY_FUNCTION__ << i << buff;
 
        QBuffer lBuf (&buff);
        lBuf.open (QIODevice::ReadOnly);
        QDataStream numStr (&lBuf);
        quint64 num;
        for (int ii=0; ii<nd2; ii++)
        {
            numStr >> num;
            qDebug () << __PRETTY_FUNCTION__ << num;
            st[ii] = num;
        }
        ...
    }

QString fileName = QFileDialog::getOpenFileName (this, tr("Select
source file"), QDir::currentPath(), tr("All files (*)"));
    if (fileName.isEmpty())
        return;
    ...

    QFile * fData = new QFile (fileName);

    for (int i=1; i<=na; i++)
    {
        char * colData = new char [nd2*sizeof (unsigned long)];
        qint64 colLength = fData->readLine (colData, nd2*sizeof
(unsigned long));
        if (colLength < 0)
        {
            qDebug () << __PRETTY_FUNCTION__ << QString ("Read error");
            continue;
        }
        QByteArray buff (colData);
        delete [] colData;
        //qDebug () << __PRETTY_FUNCTION__ << i << buff;

        QBuffer lBuf (&buff);
        lBuf.open (QIODevice::ReadOnly);
        QDataStream numStr (&lBuf);
        quint64 num;
        for (int ii=0; ii<nd2; ii++)
        {
            numStr >> num;
            qDebug () << __PRETTY_FUNCTION__ << num;
            st[ii] = num;
        }
        ...
    }

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And for the same file in debug numbers do not read properly.
Thanks a lot.

[Lesiok]

First of all why in Qt code You are using readLine ? This method is for reading character data not binary.

[YuriyRusinov]

First of all why in Qt code You are using readLine ? This method is for reading character data not binary.

I try using method read, such this

char * colData = new char [nd2*sizeof (unsigned long)];
        qint64 colLength;// = nd2*sizeof (unsigned long);
        //stStream.readBytes (colData, colLength);
        colLength = fData.read (colData, nd2*sizeof (unsigned long));
        if (colLength <= 0)
        {
            qDebug () << __PRETTY_FUNCTION__ << i << QString ("Read error");
            return;
        }
        QByteArray buff (colData);
        delete [] colData;

char * colData = new char [nd2*sizeof (unsigned long)];
        qint64 colLength;// = nd2*sizeof (unsigned long);
        //stStream.readBytes (colData, colLength);
        colLength = fData.read (colData, nd2*sizeof (unsigned long));
        if (colLength <= 0)
        {
            qDebug () << __PRETTY_FUNCTION__ << i << QString ("Read error");
            return;
        }
        QByteArray buff (colData);
        delete [] colData;

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but error was arises. Which way I have to trace this error ?

[wysota]

You forgot to open the file.

[ChrisW67]

Once you have the file open...

You are reading nd2 unsigned longs (probably 4 bytes each) from the file and then trying to extract nd2 unsigned 64-bit integers from that data (lines 26 and 29).

[YuriyRusinov]

Sorry, I skip this

if (!fData.open (QIODevice::ReadOnly | QIODevice::Unbuffered))
        return;

if (!fData.open (QIODevice::ReadOnly | QIODevice::Unbuffered))
        return;

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But nothing changes.

[wysota]

What else did you skip?

BTW. You are reading data using QDataStream. Was it written using QDataStream?

[YuriyRusinov]

Problem was in environment. I forgot define macro _FILE_OFFSET_BITS=64 in 32 bit environment. Thanks a lot.