Lockkeyword

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

Syntax

Lock #filenum, record

Lock #filenum, start To end

Parameters

Name		Description
`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.

Remarks

Differences from QB

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

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

Reference

Documented in KeyPgLock.html