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Lock Statement
This standard VB statement controls access to an open file. Syntax
Lock [#]filenumber[, [start] [To end]]
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filenumber |
The file number of the open file as used in the Open statement |
start |
A long integer representing the number of the first record or byte offset to lock or unlock |
end |
A long integer representing the number of the last record or byte offset to lock or unlock |
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 arguments. 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 CreateFile
Sub 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 Sub
Sub 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 Sub
Related Topics
Open Statement Unlock Statement
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