LOCK

The LOCK statement restricts access to parts of a file by other programs or processes.

Syntax

LOCK [#]fileNumber%

LOCK [#]fileNumber%, record&

LOCK [#]fileNumber%, [firstRecord&] TO lastRecord&

fileNumber% is the file number of the file to lock.
In the first syntax, the entire file is locked.
In the second syntax, record& is the record number of the file to lock.
In the third syntax, the records or bytes in the range [firstRecord&,lastRecord&] are locked. If firstRecord& is omitted, it is assumed to be one (the first record or byte).
For files opened in BINARY mode, each record corresponds to a single byte.
LOCK and UNLOCK statements are always used in pairs and each statement must match the other one.
Files must be unlocked using UNLOCK before other programs can access them, and before the file is closed.
Keyword not supported in Linux or macOS versions

Required DOS SHARED.EXE to be run for QBasic to use networking access modes. No longer required.