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Lock Statement
This standard VB statement controls access to an open file.
Syntax
Lock [#]filenumber[, [start] [To end]]
Returns
Not applicable
Usage
For binary mode, start and end are byte offsets. For random mode, start and end are record numbers. If start is specified without end, then only the record or byte at start is locked. If end is specified without start, then records or bytes from record number or offset 1 to end are locked.
For Input, output, and append modes, start and end are ignored and the whole file is locked.
Lock and Unlock always occur in pairs with identical parameters. Locks on open files must be removed before closing the file, or unpredictable results may occur.
Example
This example locks a file that is shared by others on a network, if the file is already in use. The second subprogram,
CreateFile
, creates the file used by the main subprogram.(general) (declarations)
Option Explicit
Declare Sub CreateFileSub CreateFile
' Put the letters A-J into the file
Dim x as Integer
Open "c:\temp001" for Output as #1
For x = 1 to 10
Write #1, Chr(x + 64)
Next x
Close #1
End SubSub Button_Click
Dim btngrp, icongrp
Dim defgrp
Dim answer
Dim noaccess as Integer
Dim msgabort
Dim msgstop as Integer
Dim acctname as String
noaccess = 70
msgstop = 16
Call CreateFile
On Error Resume Next
btngrp = 1
icongrp = 64
defgrp = 0
answer = 1
If answer = 1 then
Open "c:\temp001" for Input as #1
If Err = noaccess then
`File Locked -Aborted
Else
Lock #1
Line Input #1, acctname
Unlock #1
End If
Close #1
End If
Kill "C:\TEMP001"
End SubSee Also
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Siebel VB Language Reference Published: 18 June 2003 |