|
Syntax |
Lock [#] filenumber [,{record | [start] To end}] |
|
|
Description |
Locks a section of the specified file, preventing other processes from accessing that section of the file until the Unlock statement is issued. |
|
|
Comments |
The Lock statement requires the following parameters: |
|
|
|
Parameter |
Description |
|
|
filenumber |
Integer used by the Basic Control Engine to refer to the open file—the number passed to the Open statement. |
|
|
record |
Long specifying which record to lock. |
|
|
start |
Long specifying the first record within a range to be locked. |
|
|
end |
Long specifying the last record within a range to be locked. |
|
|
For sequential files, the record, start, and end parameters are ignored. The entire file is locked. The section of the file is specified using one of the following: |
|
|
|
Syntax |
Description |
|
|
No parameters |
Locks the entire file (no record specification is given). |
|
|
record |
Locks the specified record number (for Random files) or byte (for Binary files). |
|
|
to end |
Locks from the beginning of the file to the specified record (for Random files) or byte (for Binary files). |
|
|
start to end |
Locks the specified range of records (for Random files) or bytes (for Binary files). |
|
|
The lock range must be the same as that used to subsequently unlock the file range, and all locked ranges must be unlocked before the file is closed. Ranges within files are not unlocked automatically by the Basic Control Engine when your script terminates, which can cause file access problems for other processes. It is a good idea to group the Lock and Unlock statements close together in the code, both for readability and so subsequent readers can see that the lock and unlock are performed on the same range. This practice also reduces errors in file locks. |
|
|
Example |
This example creates test.dat and fills it with ten string variable records. These are displayed in a dialog box. The file is then reopened for read/write, and each record is locked, modified, rewritten, and unlocked. The new records are then displayed in a dialog box. Const crlf = Chr$(13) + Chr$(10) Sub Main() msg1 = "" msg1 = "" |
|
|
See Also |
||
|
|
L |
