Hi obad62,
first there's no 'readRowData' in the code you posted so I guess it's a type and should be 'readRawData' - anyhow, QDataStream::readRawData is declared as 'int QDataStream::readRawData ( char * s, int len )', so you have to pass a pointer to a 'char'-buffer and the size of the buffer. 'readRawData' then will fill the buffer with the loaded data and return the number of loaded bytes as 'int'.
BTW: You wrote you 'need to read binary data', but your code seems to be written to read string line by line from a text file. If you want to read a text file IMO you should use 'QTextStream' and its function 'readLine' instead of 'QDataStream'.
Hope that helps,
ZOPPO