R_FSize() 
 Determines the size of a file
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 Syntax
        nFileSize := R_FSize ( cInFile )

 Arguments
        cInFile         File specification of the file to be examined
                        Format  : [drive:][\path\]filename[.ext]
                        Example : C:\INVOICE\INVOICE.DBF

 Returns
        nFileSize       Size of the input file (in bytes).
                        If an error is detected (p.e. the specified input
                        file doesn't exist) the value -1 will be returned.

 Description
        Determines the size of a file

 Example
        See the example of R_Compress()