DosDupHandle

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)