NetLinx Programming Overview
11
NetLinx Programming Language Reference Guide
NetLinx allows variables to be defined as constants in the DEFINE_VARIABLE section of the program
or module, and in the
LOCAL_VAR section of a DEFINE_CALL or a DEFINE_FUNCTION. Assigning
constants is consistent with C++ programming conventions.
Variables
The role of the DEFINE_VARIABLE section is enhanced for NetLinx. The structure of a variable
definition is:
[NON_VOLATILE|VOLATILE][CONSTANT][<type>]<variable name> [= <value>]
NetLinx handles variables just like Axcess. NetLinx defaults non-array variables to the integer data types
and defaults array variables to character data type array. The variable must be explicitly declared if using
any other data type.
The
NON_VOLATILE and VOLATILE keywords specify what happens to a variable when the program is
downloaded or after a system reset.
 NON_VOLATILE variables (the default) lose their values when the program is downloaded, but
retain their values when the system resets.
 VOLATILE variables lose their values when the system is loaded and after the system resets.
If you initialize a
VOLATILE variable in the DEFINE_VARIABLE section, the variable initializes every
time the code is loaded or after a system reset. The variable initializes like it would in the
DEFINE_START section. If you initialize a NON_VOLATILE variable within the DEFINE_VARIABLE
section, the variable only initializes when the system is loaded, and it retains any changed values after
system resets.
Variables can now be defined as constant variables. Since the
DEFINE_CONSTANT section does not
allow you to explicitly declare a constant's data type, using the
CONSTANT keyword allows you to
explicitly declare the data type of a constant, and to define constant values for structures and arrays of
structures.
CONSTANT STR_TV CHAN_5 = {'KXAS', 5}
CONSTANT SINTEGER ABS_ZERO = -273
With Axcess, the DEFINE_CALL section allowed you to define local variables with the LOCAL_VAR
keyword. NetLinx expands the scope of
LOCAL_VAR beyond the DEFINE_CALL section of code. Local
variables now come in two flavors:
 LOCAL_VAR now defines a static (fixed) local variable (the next time a DEFINE_CALL is
called, the last value of the
LOCAL_VAR will be in memory unless the variable is initialized).
This is how Axcess handles variables defined with
LOCAL_VAR. NetLinx does not limit
LOCAL_VAR definitions strictly to the DEFINE_CALL section. LOCAL_VAR definitions can
appear within any statement block. This includes (but is not limited to)
DEFINE_FUNCTION,
DEFINE_EVENT, WHILE statements, WAIT statements, etc.
 STACK_VAR defines a non-static local variable. STACK_VAR defines local variables the same
way as
LOCAL_VAR, and like LOCAL_VAR, STACK_VAR can appear in any statement block.
The difference is that the value stored in the variable is initialized to zero whenever the
statement block is called, and the value is destroyed when the statement block is finished. The
structure for
LOCAL_VAR and STACK_VAR variables include:
LOCAL_VAR [NON_VOLATILE | VOLATILE] [CONSTANT] [<type>] name [= <value>]STACK_VAR
[<type>] name [= <value>]
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