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This is part of Family API which allow to create dual-os version of program runs under OS/2 and DOS
Note: This is legacy API call. It is recommended to use 32-bit equivalent
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; 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
Text based on http://www.edm2.com/index.php/DosDupHandle_(FAPI)