Basic Characteristics RAPID

Data Basic Characteristics RAPID
5 Data
5.1 Data scope
There are three kinds of data: variables, persistents and constants.
- A variable can be assigned a new value during program execution.
- A persistent can be described as a “persistent” variable. This is accomplished
by letting an update of the value of a persistent automatically cause the initialisation
value of the persistent declaration to be updated. (When a program is
saved the initialisation value of any persistent declaration reflects the current
value of the persistent.)
- A constant represents a static value and cannot be assigned a new value.
A data declaration introduces data by associating a name (identifier) with a data type.
Except for predefined data and loop variables, all data used must be declared.
The scope of data denotes the area in which the data is visible. The optional local directive
of a data declaration classifies data as local (within the module), otherwise it is global.
Note that the local directive may only be used at module level, not inside a routine.
Example: LOCAL VAR num local_variable;
VAR num global_variable;
Data declared outside a routine is called program data. The following scope rules apply
to program data:
- The scope of predefined or global program data may include any module.
- The scope of local program data comprises the module in which it is contained.
- Within its scope, local program data hides any global data or routine with the
same name (including instructions and predefined routines and data).
Program data may not have the same name as other data or a routine in the same module.
Global program data may not have the same name as other global data or a routine
in another module. A persistent may not have the same name as another persistent in
the same program.
Data declared inside a routine is called routine data. Note that the parameters of a routine
are also handled as routine data. The following scope rules apply to routine data:
- The scope of routine data comprises the routine in which it is contained.
- Within its scope, routine data hides any other routine or data with the same
name.
See the example in Figure 4.
5-20 RAPID Reference Manual