Lock

Restricts read/write access to a file or portion of a file

Syntax
   Lock #filenum, record
   Lock #filenum, start To end

Parameters
   filenum
      The file number used to Open the file.
   record
      The record (Random files) to lock.
   start
      The first byte position (Binary files) to lock from.
   end
      The last byte position (Binary files) to lock to.

Description
   Lock temporarily restricts access by other threads or programs to a 
   file, or portion of a file, usually to allow safe writing to it.

   After modifying the data, an Unlock with the same parameters as the Lock 
   should be issued.

   Note: This command does not always work, neither as documented nor as 
   expected. It appears to be broken at the moment.

Example
   '' e.g. locking a file, reading 100 bytes, and unlocking it. 
   '' To run, make sure there exists a file called 'file.ext' 
   '' in the current directory that is at least 100 bytes.

   Dim array(1 To 100) As Integer
   Dim f As Integer, i As Integer
   f = FreeFile
   Open "file.ext" For Binary As #f
   Lock #f, 1 To 100
   For i = 1 To 100
      Get #f, i, array(i)
   Next
   Unlock #f, 1 To 100
   Close #f

Differences from QB
   * Currently, FB cannot implicitly lock the entire file
   * In Random mode, FB cannot lock a range of records

See also
   * Open
   * Unlock
   * ScreenLock

