QFile. Only close() do flush()

[DungeonLords]

I use QFile. After I finish writing I do flush() and then I want readAll() file back. Why zero inside?

   QFile file;
   file.setFileName("test.bin");
   if(!file.open(QIODeviceBase::ReadWrite | QIODeviceBase::Truncate)){
       qWarning() << "err Can't open file" << file.fileName();
   }
   const quint8 myData[] = { 1,2,3 };
   file.write((const char*)myData, sizeof(myData));
   file.flush();

//    //Why to get true arr size I need close, open?
//    csvDefaults.close();
//    csvDefaults.open(QIODeviceBase::ReadWrite);

   const QByteArray arr(file.readAll());
   qDebug() << "arr size=" << arr.size();
   file.close();

I can fix my problem if I do close() and open(), but why I can't do flush() only?

Full code here.

[JonB]

@DungeonLords
This may or may not apply to QFile, I don't know, but if you open a file for read/write, write to it, then:

• After write file pointer is at end of written bytes, need to seek to beginning/rewind to read from start; and
• Many C/C++ implementations require (or at least used to) seek between write/read or read/write anyway.

And btw QFile::readAll() says "Reads all remaining data from the device", that does not mean all data in file from start, it means from file pointer onward only. As per first point above.

[mpergand]

@DungeonLords
As @JonB said, you need to reposition to the beginning of the file.

You can use:
file.seek(0);
or
file.reset();