Persistent Variables; Arrays - AMX NETLINX PROGRAMMING LANGUAGE Manual

NetLinx Programming Overview

Persistent Variables

Persistent variables have been implemented in the second release of NetLinx. Persistent variables are
NetLinx program variables that maintain their value between updates to the NetLinx program. The user
can define a variable to be persistent using the
PERSISTENT CHAR cMyString[100]
All persistent variables are automatically non-volatile. It is not legal to define a variable as
and
PERSISTENT
When a NetLinx program has a persistent variable declared, subsequent downloads of new NetLinx
programs containing the same persistent variable will retain the variable settings. By default, non-
persistent variables are set to zero after a NetLinx program download. Persistence overrides this behavior
by setting the variable in the newly downloaded program to be the same as it was before the download.
Typically, persistent variables are used for saving preset information. Suppose you have a system that
contains several PosiTrack camera positioning systems, and that the user interface to the system allows
the user to set the position of any of the cameras and record that position for recalling later. The position
presets are stored in a non-volatile array variable so they are maintained during a power cycle. Without
persistent variables, an update to the NetLinx program would zero out all of the presets the user had
stored. With persistent variables, the new NetLinx program can be downloaded and all of the presets
remain intact.
When a new NetLinx program is downloaded to the Master, the Master iterates through all non-volatile
variables from the new program looking for persistent ones. When it finds a persistent variable in the
new program, it searches the old programs persistent variable space for the same variable. When it finds
the same variable, the value of the new variable is set to the same value as the old variable. The Master
identifies the same variable by verifying the following:
Therefore, in order for persistence to function properly the name, type, and file location declared must be
the same as the previously downloaded NetLinx program. If you changed any of the three, the new
persistent variable will not be set with the old variable's value.

Arrays

Arrays are the most common way of combining a number of data items into a single unit. Axcess uses
three methods to store data in arrays:
Axcess arrays are limited to storing 255 elements per dimension. Axcess does not allow you to store
two-dimensional arrays as constants; instead, you set and initialize a two-dimensional array in the
DEFINE_START
NetLinx enhances the handling of arrays. You can define arrays of any data type in single and multi-
dimensional arrays. You can define arrays of structures, initialize arrays within the
section, and define arrays as constants.
NetLinx handles arrays similar to C++, except that the first index value of the array is 1 rather than an
index of 0 used by C++. With array initialization you don't need to count how many items are initialized.
These definitions are functionally the same:
12
.
Variable name
Variable source location
Variable type
8-bit single dimensional arrays
16-bit single dimensional arrays
8-bit two-dimensional arrays
section. You are responsible for maintaining the integrity of the initialized value.
storage modifier as show below:
PERSISTENT
NetLinx Programming Language Reference Guide
VOLATILE
DEFINE_VARIABLE