GWBASIC User's Manual

GW-BASIC User's Guide
● Files may be restricted by the implementation of an OPEN statement which allows a
process to specify an access to the successfully opened file. The access determines a
guaranteed exclusivity range on that file by the process while the OPEN statement is in
effect.
lock can be one of the following:
SHARED "deny none" mode. No restrictions are placed on the read/write accessibility
of the the file to another process, except that the default mode is not allowed
by any of the modes including SHARED.
LOCK READ "deny read" mode. Once a file is opened with the LOCK READ access, no
other process is granted read-access to that file. An attempt to open a file
with this access will be unsuccessful, if the file is currently open in default
mode or with a read access.
LOCK WRITE "deny write" mode. A file successfully opened with LOCK WRITE access
may not be opened for a write access by another process. An attempt to open
a file with this access will be unsuccessful if the file has been opened in
default mode, or with a write access by another process.
LOCK READ WRITE"deny all" or "exclusive" mode. If a file is successfully opened with this
access, the process has exclusive access to the file. A file that is currently
open in this mode cannot be opened again in any mode by any process.
default "compatibility" mode, in which the compatibility with other BASICs is
understood. No access is specified. The file may be opened any number of
times by a process, provided that the file is not currently opened by another
process. Other processes are denied access to the file while it is open under
default access. Therefore, it is functionally exclusive.
When an attempt is made to open a file that has been previously accessed by another process, the
error "Permission Denied" will result. An example of a situation generating this error is when
a process attempts to OPEN SHARED on a file that is already OPEN LOCK READ WRITE by
another process.
If an OPEN statement fails because the mode is incompatible with network-installed sharing
access to a device, the error generated is "Path/File Access Error." An example of this is
when a process is attempting to OPEN a file for output on a directory that has been shared for read
only.
For more information about using files in a networking environment, see the LOCK and
UNLOCK statements.
Examples:
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