Can't read large file (2.5GB) with QFile

[enricong]

I am trying to read a 2.5GB text file.

QFile input_file(filename);
    if (!input_file.open(QIODevice::ReadOnly))
        return;
    qint64 x = input_file.bytesAvailable();
    QString test = input_file.readLine();
    QString test2 = input_file.readAll();

QFile input_file(filename);
    if (!input_file.open(QIODevice::ReadOnly))
        return;
    qint64 x = input_file.bytesAvailable();
    QString test = input_file.readLine();
    QString test2 = input_file.readAll();

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Both test and test2 are empty.
x = 2682500677
Also, isReadble() is true, but canReadLine() is false
I can read a 5MB file with no problem.