Can't extract exe or dll files with quazip (Qt) - c++

Question

I am building a qt framework to download and install application updates (like sparkle for obj-c). The download works, the downloaded zip file is valid and i can extract the contents manually but when I let my framework unzip the contents via quazip the files (dll and exe) contains this and only this string: "MZ" and a special char which is wrong encoded (some kind of square on windows and "ê" on mac), so exactly 3 bytes. When I include a text file (or xml) in the zip file, it will be unzipped correctly, manually and with quazip, so I assume that the library was compiled correctly. Where is my error?
I think this can be part of the solution http://en.wikipedia.org/wiki/DOS_MZ_executable?
Here is my method to install the update:
QuaZip archiveWrapper(filename); // The downloaded zip file
if (archiveWrapper.open(QuaZip::mdUnzip)) {
QuaZipFile archive(&archiveWrapper);
qDebug() << "Extracting files" << archiveWrapper.getFileNameList();
for (bool more = archiveWrapper.goToFirstFile(); more; more = archiveWrapper.goToNextFile()) {
QString filePath = archiveWrapper.getCurrentFileName();
QString destinationPath = QDir::cleanPath(QDir::currentPath() + QDir::separator() + filePath);
QString destinationBackup = destinationPath + "_backup";
qDebug() << "Extract" << filePath << "to" << destinationPath;
QuaZipFile zip(archive.getZipName(), filePath);
zip.open(QIODevice::ReadOnly);
QByteArray data = zip.readAll();
zip.close();
QFile oldFile(destinationPath);
if (oldFile.exists()) {
qDebug() << "Rename" << destinationPath << "to" << destinationBackup;
if (!oldFile.rename(destinationBackup)) {
qWarning("Could not rename %s to %s!", destinationPath.toUtf8().constData(), destinationBackup.toUtf8().constData());
}
}
QFile destination(destinationPath);
destination.open(QIODevice::WriteOnly);
destination.write(data.data());
destination.close();
if (oldFile.exists()) {
qDebug() << "Deleting backup of" << destinationPath;
if (!oldFile.remove()) {
qWarning("Could not delete %s!", destinationPath.toUtf8().constData());
}
}
}
if (archive.getZipError() == UNZ_OK) {
qDebug() << "All files extracted successfully";
qDebug() << "Restarting application...";
archiveWrapper.close();
qApp->quit();
QProcess::startDetached(qApp->arguments()[0], qApp->arguments());
} else {
qWarning("Error while extracting files (Error %d)", archive.getZipError());
archiveWrapper.close();
}
} else {
qWarning("Could not open archive to extract contents");
}
Edit:
I found out that data (QByteArray) has the expected size, so I think the problem is that QFile does not write the contents of QByteArray into the exe/dll files the way it should be?
Edit 2:
I've found one error, the file size to write:
destination.write(data.data(), data.size());
instead of
destination.write(data.data());
but still, the exe does not have an icon or is executable (but with the correct file size). For a short time a dos window opens and closes. There is a antivirus software running but there is no alert (and because this is a corporate notebook i am not able to shut it down and the update framework should also be running whether there is a antivirus software running or not).
Edit 3:
Although I thought writing exe files is complicated, it was a mixture of stupid bugs I "implemented" for testing purposes. So the simple
QFile destination(destinationPath);
destination.open(QIODevice::WriteOnly);
destination.write(data.data(), data.size())
is sufficient.