====== SVC_DUPHANDLE ======

Duplicate a file handle. This call creates a new file handle that refers to the same open file, pipe, or device as an existing handle.

===== Brief =====

Duplicate file handle (INT 21h AH=45h)

===== Input =====

  * BX = existing file handle

===== Return =====

  * CF clear if successful
    * AX = new handle
  * CF set on error
    * AX = [[en:docs:mvm:api:errors|error code]] (04h, 06h)

===== Notes =====

  * Both handles refer to the same system file table entry. Moving the file pointer for one handle also moves it for the other.
  * Closing one handle does not affect the other until both are closed.
  * The new handle has the same access rights and sharing mode as the original.

===== Binding =====

==== MASM ====

<code asm>
include macrolib.inc

    mov bx, handle
    @SvcDupHandle

handle dw 1234h
</code>

==== C ====

<code c>
#include <svc.h>

unsigned short newhandle;
unsigned short oldhandle = 0x1234;

newhandle = SvcDupHandle(oldhandle);
</code>

The underlying pragma is defined as:

<code c>
extern unsigned short SvcDupHandle(unsigned short handle);
#pragma aux SvcDupHandle = \
    "hlt"           \
    "db  0"         \
    "db  NOT 0"     \
    parm [bx]       \
    value [ax]      \
    modify [ax bx cx dx];
</code>

===== See also =====

  * [[en:docs:dos:api:int21:45|INT 21h AH=45h]] – DOS duplicate handle

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