This call moves the read/write pointer in accordance with the type of move specified.

Syntax

DosChgFilePtr (FileHandle, Distance, MoveType, NewPointer)

Parameters

;FileHandle (HFILE) - input : Handle returned by a previous DosOpen call. ; Distance (LONG) - input : The offset to move, in bytes. ; MoveType (USHORT) - input : Method of moving. Specifies a location in the file from where Distance to move the read/write pointer starts. Values and their meanings are: 'Value Definition' 0 Beginning of the file. 1 Current location of the read/write pointer. 2 End of the file. Use this method to determine a file's size. ; NewPointer (PULONG) - output : Address of the new pointer location.

Return Code

rc (USHORT) - return Return code descriptions are: * 0 NO_ERROR * 1 ERROR_INVALID_FUNCTION * 6 ERROR_INVALID_HANDLE

Remarks

The read/write pointer in a file is a signed 32-bit number. A negative value moves the pointer backward in the file. A positive value moves the pointer forward. DosChgFilePtr cannot be used to seek to a negative position in the file.

This call may not be used for a character device or pipe.

Example Code

C Binding

<PRE> #define INCL_DOSFILEMGR

USHORT rc = DosChgFilePtr(FileHandle, Distance, MoveType, NewPointer);

HFILE FileHandle; /* File handle */ LONG Distance; /* Distance to move in bytes */ USHORT MoveType; /* Method of moving (0, 1, 2) */ PULONG NewPointer; /* New Pointer Location */

USHORT rc; /* return code */ </PRE> This example opens file test.dat, writes some data, and resets the file pointer to the beginning of the file. <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; USHORT Wrote; USHORT Action; PUSHORT Local 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) */
if(!DosWrite(FileHandle, /* File handle */
(PVOID) FileData, /* User buffer */
sizeof(FileData), /* Buffer length */
&Wrote)) /* Bytes written */
rc = DosChgFilePtr(FileHandle, /* File handle */
MOVE_DIST, /* Distance to move in bytes */
FILE_BEG, /* Method of moving */
&Local); /* New pointer location */

</PRE>

MASM Binding

<PRE> EXTRN DosChgFilePtr:FAR INCL_DOSFILEMGR EQU 1

PUSH WORD FileHandle ;File handle PUSH DWORD Distance ;Distance to move in bytes PUSH WORD MoveType ;Method of moving (0, 1, 2) PUSH@ DWORD NewPointer ;New Pointer Location (returned) CALL DosChgFilePtr

Returns WORD </PRE>