Variable Reference

Help Contents

Introduction

A variable reference indicates the location of a program variable. These can be used to:

Read the value of a variable in an Expression.
Map an output parameter in a Function called from an expression.
Write a value to a variable using a structured text Assignment Statement.
Declare the loop variable in a structured text FOR Loop.
Declare an output parameter in a structured text Function Call.
Declare the target of a ST, S or R instruction in an Instruction List.

A variable reference can be:

A simple Identifier.
A reference to an element of an Array.
A reference to a member variable of a Struct.
A Tag Reference.

Examples

A reference a program variable uses an Identifier:
```
SampleCount
```
A reference to an element of an Array:
```
ConveyorLoads[1]
```
A reference to a member of a Struct:
```
ItemLocation.Distance
```
A Tag Reference:
```
%"Pressure.Value"
```

The above examples use the following Variable Declarations:

TYPE
    PolarCoordinates : STRUCT
        Angle : LREAL;
        Distance : LREAL;
    End_STRUCT
End_TYPE
VAR
    SampleCount : LREAL;
    ConveyorLoads : ARRAY [0..5] OF REAL;
    ItemLocation : PolarCoordinates;
End_VAR

Further Information

Array

To learn about array types and how to reference array elements.

Struct

To learn about struct types and how to reference structure members.

Pointer

To learn about pointer types and how to dereference pointer values.

Glossary

For the meaning of terms used in Fernhill SCADA.