QDataStream write file size to file header ?

sonichy

QDataStream write 4 more bytes to file header which seems like file size, and causes file error, file.write() will not.

QFile file(path);
if (file.open(QFile::WriteOnly)) {
    QDataStream DS(&file);
    QByteArray BA = "aaaaaaaaaaa";
    DS << BA;
    file.close();
}

QFile file(path);
if (file.open(QFile::WriteOnly)) {    
    QByteArray BA = "aaaaaaaaaaa";
    file.write(BA);
    file.close();
}

Christian Ehrlicher

And what's the actual problem? QDataStream is an internal stream format which allows you to write and read Qt data types directly to a file. Therefore it need to add some information to know which data type is there and others like e.g. it's content size.

VRonin

those 4 bytes are the lenght of the array so that you can read it back otherwise you wouldn't know where to stop...

Source: https://code.woboq.org/qt5/qtbase/src/corelib/serialization/qdatastream.cpp.html#_ZN11QDataStream10writeBytesEPKcj

Gojir4