Function 46h (70)        Force Handle Duplication (FORCDUP)

Force one handle to refer to the same file as another handle. (Both
handles must already exist.)

On entry:      AH         46h
BX         First file handle
CX         Handle to be changed

Returns:       AX         Error code, if CF is set

Error codes:   4          No handles available
6          Invalid handle

Call Function 59h for extended error code information
(DOS 3.0 and above).

                                                                          

This function causes the second handle (in CX) to refer to the same
file, at the same location, as the first handle (in BX). If the second
handle refers to an open file, that file is closed before the handle
is set equal to the first handle.

Notes:         Moving the file pointer of either handle by a Read,
Write, or Lseek causes the other handle to be
changed also. However, closing one handle does not
close the other.

This function is useful for redirection. For
example, to redirect standard output (predefined as
Handle 1) to a file, place 1 in CX, and in BX place
the handle for the file to which output is to be
redirected.

See also: 45h
See also: 59h

46h (70) Force Handle Duplication (FORCDUP)