i have found the solusion
QString open_file = QFileDialog::getOpenFileName(this,"open file","/home path");
QFile file01(open_file);
now if you want to use the file for any operation you like
for example (get the file name or size) just use (file01)
to do operations on
by the way there's 2 types of files on QFileDialog
1. Static File....example ("/home/user/documents/file01.iso")
2. Dynamic File...example (the file that the user WILL pick from Open Dialog)
i hope this will be clear to the beginners like myself