vfs.move-cursor

function

Library: File system utilities (OMVFS)
Import : omvfs.xmd

Declaration

export external function move-cursor
        of      value file file-ref
        by      value integer offset optional
        to      value integer absolute optional

Argument definitions

file-ref: A vfs.file object representing the file in which the cursor is to be moved.

offset: The distance to move the cursor relative its current position.

absolute: The absolute position to move the cursor to.

Purpose

You can use vfs.move-cursor to change the position at which the next read of a file will occur. The position may be specified either relative to the current cursor position, or as an absolute position in a file. For instance, if you know that the data you are interested in starts at byte 100 in a file, you can read from that position like this:

  import "omvfs.xmd" prefixed by vfs.
  
  process
     local vfs.file test-file
     set test-file
      to vfs.open "c:/omnimark/projects/testfile.txt"
     vfs.move-cursor of test-file to 100
     output vfs.reader of test-file

You must specify either a relative or absolute movement, and not both.

Exceptions

The following exceptions may occur:

VFS200 The vfsFile object must be opened before it can be used
VFS204 The file 'X' must not have an active output or source associated with it
VFS209 An invalid value was specified for the absolute cursor movement
VFS210 Absolute and relative cursor movement may not both be specified
VFS211 The cursor cannot be positioned before the start of the file
VFS300 Generic operating system error

Related Topics