Use QXmlStreamWriter to modify existing elements

[Lykurg]

the file is loaded in memory and changes are done in memory... to save the changes back in file just open the same file with writeonly(to erase old contents) and then save

void QDomNode::save ( QTextStream & str, int indent ) const

That's principal right, but I guess you want to read the value somewhere else in your program. So every time open, save, read in elsewhere is not very good. Therefore only create one instance and pass a pointer of the QDomDocument to the needed classes, or use a singleton approach.