Assembly Language Help (alang.hlp) (Table of Contents; Topic list)
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Int 21h Function 45h
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  Interrupt:   21h     Function:     45h
 
  Title:       Duplicate Handle
 
  See also:    Redirect Handle, Open File
 
  Description:
 
     Given a handle for a currently open device or file, this function
     returns a new handle that refers to the same device or file at the
     same position.
 
     Input                            Output
 
     AH = 45h                         If function successful
     BX = Handle to be duplicated       Carry flag: clear
                                        AX = New handle
 
                                      If function unsuccessful
                                        Carry flag: set
                                        AX = Error code (04h or 06h)
                                        See: Error codes
                                    -♦-