how to read a file that greater than 4G?

[weixj2003ld]

How to read a file that is greater than 4G with Qt?

thank you.

[ChrisW67]

The same way you do a smaller file. You just need to use long long integers more carefully.

#include <QtCore>
#include <QDebug>
 
int main(int argc, char **argv)
{
    QCoreApplication app(argc, argv);
 
    QFile file("test.dat");
    qDebug() << file.size();
    if (file.open(QIODevice::ReadOnly)) {
        bool ok = file.seek( 4097 * 1024 * 1024LL  ); 
        qDebug() << ok;
        QByteArray data = file.read(1024);
        qDebug() << data.size();
        file.close();
    }
    return 0;
}

#include <QtCore>
#include <QDebug>

int main(int argc, char **argv)
{
    QCoreApplication app(argc, argv);

    QFile file("test.dat");
    qDebug() << file.size();
    if (file.open(QIODevice::ReadOnly)) {
        bool ok = file.seek( 4097 * 1024 * 1024LL  ); 
        qDebug() << ok;
        QByteArray data = file.read(1024);
        qDebug() << data.size();
        file.close();
    }
    return 0;
}

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output for my test file:

4299161600 
true 
1024

4299161600 
true 
1024

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[weixj2003ld]

thank you.
I know that in C++/C,the seek function has a start mode(current ,begin,or end),but the seek method of QFile has no the parameter,where does it begin from where the position move forward?

[ChrisW67]

In a random-access file it seeks to the specified byte starting from the front of the file, just like fseek() with SEEK_SET. Combine it with QFile::pos() and QFile::size() to get other behaviours.