{{page>en:templates:dosint}}

====== Int 21H, AH=42H ======

===== Version =====

2 and higher

===== Brief =====

"LSEEK" - SET CURRENT FILE POSITION

===== Family API =====


===== Input =====

        AH = 42h
        AL = origin of move
            00h start of file
            01h current file position
            02h end of file
        BX = file handle
        CX:DX = (signed) offset from origin of new file position

===== Return =====

 CF clear if successful
            DX:AX = new file position in bytes from start of file
        CF set on error
            AX = error code (01h,06h) (see #01680 at AH=59h/BX=0000h)

===== Notes =====

  for origins 01h and 02h, the pointer may be positioned before the
          start of the file; no error is returned in that case (except under
          Windows NT), but subsequent attempts at I/O will produce errors
        if the new position is beyond the current end of file, the file will
          be extended by the next write (see AH=40h); for FAT32 drives, the
          file must have been opened with AX=6C00h with the "extended size"
          flag in order to expand the file beyond 2GB
  BUG:    using this method to grow a file from zero bytes to a very large size
          can corrupt the FAT in some versions of DOS; the file should first
          be grown from zero to one byte and then to the desired large size
          
===== See also =====

 AH=24h,INT 2F/AX=1228h

===== Note =====

Text based on [[http://www.cs.cmu.edu/~ralf/files.html|Ralf Brown Interrupt List Release 61]]

{{page>en:templates:int}}

{{page>en:templates:fapi}}