Prevents access to all or specific portions of a file by network programs.
LOCK [#]file_number [,{record_number |
[ start] TO end}] |
file_number is the file number assigned to the file in its OPEN statement.
For random-access files, LOCK locks the specified record or range of records. For binary files, LOCK locks the specified byte or range of bytes. For sequential files, LOCK locks the entire file.
LOCK is necessary only in network environments.
If a network program tries to access a locked record or byte, QBasic generates an error.
To use LOCK, you should first run the SHARE.EXE program, an MS-DOS program that supports file sharing and locking.
INPUT "Enter record number to update"; rec
LOCK #1, rec 'Restrict access
emp.name$ = "SMITH"
PUT #1, rec
UNLOCK rec 'Allow access