Using Caché ObjectScript - InterSystems Documentation

Categories of Variables
• A global name must be unique within its namespace.
• Global names are limited to 31 characters, exclusive of the prefix characters. You may specify a name longer than 31
characters, but only the first 31 characters are used. Therefore, a global name must be unique within its first 31 characters.
• Globals can take subscripts. By using subscripts, you can define a global as an array of values. For naming conventions,
limitations on the number of subscript levels, and other information about use of subscripts, refer to Global Structure
in Using Caché Globals.
Optionally, a global may specify an extended reference that defines its namespace or directory using a pair of vertical bars
or square brackets immediately after the caret characters (for example: ^|"samples"|myglobal or ^|""|myglobal).
These extended global references should not be confused with process-private globals.
You can use the $ZREFERENCE special variable to determine the name of the most recently used global. You can use the
$QSUBSCRIPT function to return the components of a specified global, or the $QLENGTH function to return the number
of subscript layers.
For much more information on globals, refer to Using Caché Globals.
4.1.4 Array Variables
An array variable is simply a variable with one or more subscript levels. Subscripts are enclosed in parentheses. Subscript
levels are separated by commas. Any variable (with the exception of special variables) can be used as an array, as shown
in the following example:
SET a(1) = "A local variable array"
SET a(1,1,1) = "Another local variable array"
SET ^||a(1) = "A process-private global array"
SET ^a(1) = "A global array"
SET obj.a(1) = "A multidimensional array property"
For local variables, the maximum number of subscript levels is 255. For global variables, the maximum number of subscript
levels depends on the length of the subscript names. For subscript naming conventions and limits, refer to the Global
Structure chapter in Using Caché Globals.
4.1.5 Special Variables
Caché ObjectScript includes a number of built-in special variables (also referred to as system variables) that are used to
make certain system information available to applications. All special variables are supplied with Caché and are named
with a “$” character prefix. Users cannot define additional special variables. The set of special variables is mapped to be
accessible from all namespaces.
The value of a special variable is set to the current state of some aspect of your operating environment. Some special variables
are initially set to the null string (""); referencing a special variable should never generate an error. The
value of a special variable is specific to the current process and cannot be accessed from another process.
Users can set some special variables with the SET command; other special variables are not user-modifiable. Refer to the
individual special variables for further details.
The following example uses the special variable $HOROLOG:
SET starttime = $HOROLOG
HANG 5
WRITE !,$ZDATETIME(starttime)
WRITE !,$ZDATETIME($HOROLOG)
The special variable $HOROLOG stores the current system date and time. The SET command uses this special variable
to set the user-defined local variable starttime to this value. The HANG command then suspends the program for 5 seconds.
Finally, the two $ZDATETIME functions return starttime and the current system date and time in a user-readable format.
Using Caché ObjectScript 27