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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.
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.
Example Code
C Binding
<PRE> #define INCL_DOSFILEMGR
USHORT rc = DosDupHandle(OldFileHandle, NewFileHandle);
HFILE OldFileHandle; /* Existing file handle */ PHFILE NewFileHandle; /* New file handle (returned) */
USHORT rc; /* return code */ </PRE> This example opens a file, creates a second file handle, then closes the file with the second handle.
<PRE> #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 */
</PRE>
MASM Binding
<PRE> EXTRN DosDupHandle:FAR INCL_DOSFILEMGR EQU 1
PUSH WORD OldFileHandle ;Existing file handle PUSH@ WORD NewFileHandle ;New file handle (returned) CALL DosDupHandle
Returns WORD </PRE>
Note
Text based on http://www.edm2.com/index.php/DosDupHandle_(FAPI)