Name
Lock Procedure
Class
Microsoft.VisualBasic.FileSystem
Syntax
Lock(filenumber
[,record
])
or:
Lock(filenumber
[,fromrecord,torecord
]
-
filenumber
(required; Integer) Any valid file number
-
record
(optional; Long) The record or byte number at which to commence the lock
-
fromrecord
(optional; Long) The first record or byte number to lock
-
torecord
(optional; Long) The last record or byte number to lock
Description
The Lock procedure prevents another process from accessing a record, section, or whole file until it is unlocked by the Unlock function.
Use the Lock procedure in situations where multiple programs or more than one instance of your program may need read and write access to the same data file.
Rules at a Glance
Use the Lock procedure with only the
filenumber
argument to lock the whole file.record
is interpreted as a record number in the case of random files and a byte number in the case of binary files. Records and bytes in a file are always numbered sequentially from 1 onward.To lock a particular record, specify its record number as
record
, and only that record will be locked.The Lock procedure locks an entire file opened in Input or Output (sequential) mode, regardless of the
record
argument.If you omit the
start
argument, Lock will lock all records from the start of the file to record or byte numberend
.Attempting to access a locked file or portion of a file returns runtime error 70, “Permission denied.”
Programming Tips and Gotchas
You must take care to remove all file locks ...
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