Index and Assign Values to Stateflow Structures

This example shows how to access and modify the contents of a Stateflow® structure or an array of Stateflow structures. A Stateflow structure is a data type that you define from a Simulink.Bus (Simulink) object. You can use Stateflow structures to bundle data of different sizes and types together into a single data object. For more information, see Access Bus Signals.

Index Substructures and Fields

To index substructures and fields of Stateflow structures, use dot notation. The first part of a name identifies the parent structure. Subsequent parts identify the children along a hierarchical path. The children can be individual fields or fields that contain other structures (also called substructures). The names of the fields of a Stateflow structure match the names of the elements of the Simulink.Bus object that defines the structure. When a field contains a vector, matrix, or array, you can access its elements by using the indexing notation supported by the action language of your chart.

For example, the chart in this model contains an input structure (in), an output structure (out), a local structure (localbus), and a local array of structures (subBusArray).

• The chart defines the input structure in, the output structure out, and the local structure localbus by using the Simulink.Bus object BusObject. These structures have four fields: sb, a, b, and c.

• The field sb is a substructure defined from the Simulink.Bus object SubBus. This substructure has one field called ele.

• The chart defines the local array of structures subBusArray by using the Simulink.Bus object SubBus. The array has size 4. Each element in the array is a structure with one field called ele.

This list illustrates expressions that combine dot notation and numeric indices based on the structure specifications for this example:

• in.c — Field c of the input structure in

• in.a(1) — First element of the vector field a of the input structure in

• out.sb — Substructure sb of the output structure out

• out.sb.ele — Field ele of the substructure out.sb

• out.sb.ele(2,2) — Element in the second row, second column of the field ele of the substructure out.sb

• subBusArray(1) — First element of the array of structures subBusArray

• subBusArray(1).ele — Field ele of the structure subBusArray(1)

• subBusArray(1).ele(3,4) — Element in the third row, fourth column of the field ele of structure subBusArray(1)

Because the chart uses MATLAB® as the action language, you access the elements of the arrays in this example by using one-based indexing delimited by parentheses. In charts that use C as the action language, use zero-based indexing delimited by brackets. For more information, see Operations for Vectors and Matrices in Stateflow.

Assign Values to Structures and Fields

You can write to any Stateflow structure that has a scope other than Input. You can assign values to the entire structure, to a substructure, or to a single field.

• To assign one structure to another structure, define both structures from the same Simulink.Bus object in the base workspace.

• To assign one structure to a substructure of a different structure (or the other way around), define the structure and substructure from the same Simulink.Bus object.

• To assign a field of one structure to a field of another structure, the fields must have the same type and size. You can define the Stateflow structures from different Simulink.Bus objects.

For instance, the chart in this example makes these assignments:

• localbus = sb2abc(in.sb) — The structure localbus and the output argument of the MATLAB function sb2abc are defined from the same Simulink.Bus object BusObject. The function decomposes its input into three components: a vector, a 3-by-2 matrix, and a scalar. The function returns these components as the fields a, b, and c of its output. For more information on this function, see Access Simulink Bus Signals in MATLAB Functions.

• subBusArray(1) = in.sb — The structure subBusArray(1) and the substructure in.sb are defined from the same Simulink.Bus object SubBus.

• subBusArray(2) = abc2sb(in) — The structure subBusArray(2) and the output argument of the graphical function abc2sb are defined from the same Simulink.Bus object SubBus. The function combines the values of the fields a, b, and c from its input and rearranges them in a 3-by-3 matrix of type int8. It returns this matrix as the field ele of its output.

• subBusArray(3).ele = transpose(in.sb.ele) — The field subBusArray(3).ele has the same type and size as the result of transpose(in.sb.ele). Both are 3-by-3 matrices of type int8.

• subBusArray(4).ele = int8(magic(3)) — The field subBusArray(4).ele has the same type and size as the result of int8(magic(3)). Both are 3-by-3 matrices of type int8.

• out = localbus — Both out and localbus are defined from the same Simulink.Bus object BusObject.

• out.sb = subBusArray(idx) — The substructure out.sb and the structure subBusArray(idx) are defined from the same Simulink.Bus object SubBus.

Run the Simulation

When you simulate the example, the chart uses the values of the field sb of the input structure to populate the fields a, b, and c of the output structure. The parameter idx selects the element of the array of structures subBusArray to use as the substructure sb of the output. In this example, idx equals 2, so the chart uses the values of the fields a, b, c of the input structure to populate the substructure.

When you use other values for idx, the substructure out.sb contains the same values as in.sb, the transpose of in.sb, or a 3-by-3 magic square.