VB.NET Language in a Nutshell, Second Edition

Name

Unlock Procedure

Class

Microsoft.VisualBasic.FileSystem

Syntax

Unlock(filenumber[, record)

Unlock(filenumber[, fromrecord[, torecord]])

filenumber (required; Integer)

Any valid file number

record (required; Long)

The record or byte number at which to commence the lock

fromrecord (required; Long)

The first record or byte number to lock

torecord (required; Long)

The last record or byte number to lock

Description

Use the Unlock procedure in situations where more than one part of your program may need read and write access to the same data file. The Unlock procedure removes a lock that the Lock procedure placed on a section of the file or the whole file.

Rules at a Glance

• Use the Unlock procedure only with the filenumber parameter to unlock the whole file.

• The Unlock procedure unlocks an entire file opened in Input or Output (sequential) mode, regardless of the record, fromrecord, or torecord arguments.

• Records and bytes in a file are always numbered sequentially from 1 up.

• To unlock a particular record, specify its record number as record, and only that record will be unlocked.

• To unlock a range of bytes (in a binary file) or of records (in a random file), indicate the starting position as fromrecord and the ending position as torecord.

Programming Tips and Gotchas

• You must take care to remove all file locks using the Unlock procedure before either closing a file or ending the application; otherwise, you can leave the file in an unstable state. This means that, where appropriate, your error-handling ...