how to use progress bar with file transfer

["gtk rapp-informatik de" <gtk rapp-informatik de>]

HI
who can give me a working example how to use the progress bar
to show longer copy transfer amount of bytes to a file or devive
I have no idea how to get this informations calling  cpio or tar.
Or is ther another solution?
C examples are wellcome.

Thanks
Günther

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