S_DB

 Function
  Set the share deny both (read and write) flag in a FCREATE/FOPEN/FAPPEND
  statement.

 Value
  3 = 11b = 3o = 3h

 Remarks
  DOS 3.1 or later (which is what is required by PCBoard) allows processes
  to decide what mode of file sharing should be allowed.  This constant
  allows you to specify that other processes may not open the same file
  for either read or write access from the time you open the file to the
  time you close the file.  This is useful when you need exclusive access
  to a file for any reason and need to restrict other processes access to
  the same file.

 Example

  FOPEN 1,"FILE.DAT",O_RD,S_DB ' Deny other processes all access
  FOR i = 1 TO 10
   FGET 1,s
   PRINTLN s
  NEXT
  FCLOSE 1 ' Close the file and allow others to open it in any mode