Structure Operations

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Indexing Sub-Structures and Fields Guidelines for Assignment of Values Getting Addresses

Indexing Sub-Structures and Fields

You index substructures and fields of Stateflow structures by using dot notation. With dot notation, the first text string identifies the parent object, and subsequent text strings identify the children along a hierarchical path. When the parent is a structure, its children are individual fields or fields that contain other structures (also called substructures). By default, the names of the fields of a Stateflow structure match the names of the elements of the Simulink.Bus object that defines the structure.

Suppose that you have the following model:

In this example, the SubBus and BusObject blocks to the left of the chart are Bus Creator blocks. The BusObject block to the right of the chart is a Bus Selector block.

The following structures are defined in the chart:

Name of Structure	Scope	Defined By Simulink.Bus Object
in	Input	BusObject
out	Output	BusObject
subbus	Local	SubBus

The Simulink.Bus objects that define these structures have the following elements:

By default, Stateflow structures in and out have the same fields — sb, a, b, and c — as the elements of Simulink.Bus object BusObject. Similarly, the Stateflow structure subbus has the same field ele as the element of Simulink.Bus object SubBus. Based on these specifications, the following table shows how the Stateflow chart resolves symbols in dot notation for indexing fields of the structures in this example:

Dot Notation	Symbol Resolution
in.c	Field c of input structure in
in.a[1]	Second value of the vector field a of input structure in
out.sb	Substructure sb of output structure out
in.sb.ele[2][3]	Value in the third row, fourth column of field ele of substructure sb of input structure in
subbus.ele[1][1]	Value in the second row, second column of field ele of local structure subbus

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Guidelines for Assignment of Values

You can assign values to any Stateflow structure except input structures — that is, a structure with scope equal to Input. Here are the guidelines for assigning values to output, local, parameter, and temporary structures:

Operation	Conditions
Assign one structure to another structure	You must define both structures with the same Simulink.Bus object in the base workspace.
Assign one structure to a substructure of a different structure and vice versa	You must define the structure with the same Simulink.Bus object in the base workspace as the substructure.
Assign a field of one structure to a field of another structure	The fields must have the same type and size. Note   In this case, you do not need to define the Stateflow structures with the same Simulink.Bus object in the base workspace.

For example, the following table presents valid and invalid structure assignments based on specifications for the sfbus_demo model, as described in Example of Stateflow Structures:

Assignment	Valid or Invalid?	Rationale
outbus = inbus;	Valid	Both outbus and inbus are defined by the same Simulink.Bus object, COUNTERBUS.
inbus = outbus;	Invalid	You cannot write to input structures.
inbus.limits = outbus.limits;	Invalid	You cannot write to fields of input structures.
counterbus_struct = inbus;	Valid	Both counterbus_struct and inbus are defined by the same Simulink.Bus object, COUNTERBUS.
counterbus_struct.inputsignal = inbus.inputsignal;	Valid	Both counterbus_struct.inputsignal and inbus.inputsignal have the same type and size because they each reference field inputsignal, a substructure of the Simulink.Bus object COUNTERBUS.
outbus.limits.upper_saturation_limit = inbus.inputsignal.input;	Valid	The field upper_saturation_limit from limits, a substructure of COUNTERBUS, has the same type and size as the field input from inputsignal, a different substructure of COUNTERBUS.
outbus.limits = inbus.inputsignal;	Invalid	The substructure limits is defined by a different Simulink.Bus object than the substructure inputsignal.

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Getting Addresses

When you write custom functions that take structure pointers as arguments, you must pass the structures by address. To get addresses of Stateflow structures and structure fields, use the & operator, as in the following examples:

• &in — Address of Stateflow structure in

• &in.b — Address of field b in Stateflow structure in

The model sfbus_demo contains a custom C function counterbusFcn that takes structure pointers as arguments, defined as follows in a custom header file:

...
extern void counterbusFcn
            (COUNTERBUS *u1, int u2, COUNTERBUS *y1, int *y2);
...

To call this function, you must pass addresses to two structures defined by the Simulink.Bus object COUNTERBUS, as in this example:

counterbusFcn(&counterbus_struct, u2, &outbus, &y2);

See Example of Stateflow Structures for a description of the structures defined in sfbus_demo.

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Defining Stateflow Structures

Integrating Custom Structures in Stateflow Charts

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