This call returns a new file handle for an open file, which refers to the same position in the file as the old file handle.

DosDupHandle (OldFileHandle, NewFileHandle)

• OldFileHandle (HFILE) - input : Current file handle.
• NewFileHandle (PHFILE) - input/output : Address of a Word. On input, values and their meanings are:
  • FFFFH - Allocate a new file handle and return it here.
  • <>FFFFH - Assign this value as the new file handle. A valid value is any of the handles assigned to standard I/O, or the handle of a file currently opened by the process.
• On output, a value of FFFFH returns a value for NewFileHandle, allocated by OS/2.

rc (USHORT) - return

Return code descriptions are:

• 0 NO_ERROR
• 4 ERROR_TOO_MANY_OPEN_FILES
• 6 ERROR_INVALID_HANDLE
• 114 ERROR_INVALID_TARGET_HANDLE

Duplicating the handle duplicates and ties all handle-specific information between OldFileHandle and NewFileHandle. For example, if you move the read/write pointer of either handle by a DosRead, DosWrite, or DosChgFilePtr function call, the pointer for the other handle is also changed.

The valid values for NewFileHandle include the following handles for standard I/O, which are always available to the process:

• 0000H Standard input
• 0001H Standard output
• 0002H Standard error.

If a file handle value of a currently open file is specified in NewFileHandle, the file handle is closed before it is redefined as the duplicate of OldFileHandle. Avoid using arbitrary values for NewFileHandle.

Issuing a DosClose against a file handle does not affect the duplicate handle.

#define INCL_DOSFILEMGR

USHORT  rc = DosDupHandle(OldFileHandle, NewFileHandle);

HFILE            OldFileHandle; /* Existing file handle */
PHFILE           NewFileHandle; /* New file handle (returned) */

USHORT           rc;            /* return code */

This example opens a file, creates a second file handle, then closes the file with the second handle.

#define INCL_DOSFILEMGR

#define OPEN_FILE 0x01
#define CREATE_FILE 0x10
#define FILE_ARCHIVE 0x20
#define FILE_EXISTS OPEN_FILE
#define FILE_NOEXISTS CREATE_FILE
#define DASD_FLAG 0
#define INHERIT 0x80
#define WRITE_THRU 0
#define FAIL_FLAG 0
#define SHARE_FLAG 0x10
#define ACCESS_FLAG 0x02

#define FILE_NAME "test.dat"
#define FILE_SIZE 800L
#define FILE_ATTRIBUTE FILE_ARCHIVE
#define RESERVED 0L

HFILE   FileHandle;
HFILE   NewHandle
USHORT  Wrote;
USHORT  Action;
PSZ     FileData[100];
USHORT  rc;

 Action = 2;
 strcpy(FileData, "Data...");
 if(!DosOpen(FILE_NAME,                /* File path name */
              &FileHandle,             /* File handle */
              &Action,                 /* Action taken */
              FILE_SIZE,               /* File primary allocation */
              FILE_ATTRIBUTE,          /* File attribute */
              FILE_EXISTS | FILE_NOEXISTS,              /* Open function
                                                                   type */
              DASD_FLAG | INHERIT |            /* Open mode of the file */
              WRITE_THRU | FAIL_FLAG |
              SHARE_FLAG | ACCESS_FLAG,
              RESERVED))               /* Reserved (must be zero) */
    rc = DosDupHandle(FileHandle,      /* Existing file handle */
                      &NewHandle);     /* New file handle */

EXTRN  DosDupHandle:FAR
INCL_DOSFILEMGR     EQU 1

PUSH   WORD    OldFileHandle ;Existing file handle
PUSH@  WORD    NewFileHandle ;New file handle (returned)
CALL   DosDupHandle

Returns WORD

Text based on http://www.edm2.com/index.php/DosDupHandle_(FAPI)