en:docs:fapi:doschgfileptr

DosChgFilePtr

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

#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 */

This example opens file test.dat, writes some data, and resets the file pointer to the beginning of the file.

#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 */

MASM Binding

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

Note

en/docs/fapi/doschgfileptr.txt · Last modified: 2018/09/02 14:52 by prokushev