LOCK

• Source: https://www.freebasic.net/wiki/wikka.php?wakka=KeyPgLock
• Last revised: 2017-11-21

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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.

Examples

start GeSHi

'' 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

end GeSHi

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

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