DosChgFilePtr (FileHandle, Distance, MoveType, NewPointer)

;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.

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

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.

<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>

<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>