DosDupHandle (FAPI)

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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.

Syntax

DosDupHandle (OldFileHandle, NewFileHandle)

Parameters

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.

Return Code

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

Remarks

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.

Bindings

C

#define INCL_DOSFILEMGR

USHORT  rc = DosDupHandle(OldFileHandle, NewFileHandle);

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

USHORT  rc;            /* return code */

MASM

EXTRN  DosDupHandle:FAR
INCL_DOSFILEMGR     EQU 1

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

Returns WORD

Example

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 */