Differences Between MATLAB and C as Action Language Syntax

Stateflow^® charts in Simulink^® models have an action language property that defines the syntax for state and transition actions. The icon in the lower-left corner of the chart canvas indicates the action language for the chart:

MATLAB^® is the action language.
C is the action language.

The action language you choose affects how you write state and transition actions, what operations are available, and how your charts generate code.

MATLAB is the default action language syntax for new Stateflow charts. To create a chart that uses C as the action language, enter:

sfnew -c

Choosing an Action Language

Use MATLAB as the action language for:

Prototyping and rapid development, where you need to iterate quickly on algorithms and logic.
Matrix and vector operations, where your charts work extensively with arrays and complex mathematical operations.
MATLAB integration, where you want to leverage existing MATLAB functions and toolboxes.

Use C as the action language for:

Performance-critical applications where you need maximum execution speed for real-time systems.
Embedded targets and code generation for resource-constrained hardware.
Applications that contain deterministic behavior, where you need predictable timing and memory usage.

Differences in Action Languages

The MATLAB and C action languages differ in syntax, supported operations, and code generation behavior. These tables list the most significant differences between the two action languages.

Basic Operations

Functionality	MATLAB as the Action Language	C as the Action Language
Increment and decrement operations	The chart automatically corrects syntax to MATLAB syntax. For example, `a++` is corrected to `a = a+1`.	The chart supports the `a++` and `a--` supported. See Operations for Stateflow Data.
Assignment operations	The chart automatically corrects syntax to MATLAB syntax. For example, `a += b` is corrected to `a = a+b`.	The chart supports the `a += b`, `a –= b`, `a *= b`, and `a /= b` supported. See Operations for Stateflow Data.
Comparison operations	`a ~= b`	The chart supports the `a != b` and `!a` operations. See Operations for Stateflow Data.
Comment markers	Auto-correction to `%`.	The chart supports the `//` and `/* */` supported. See Operations for Stateflow Data.
Conditional statements	You can use `if`, `for`, and `while` statements in state actions. See Loops and Conditional Statements.	Supported in state actions only.
Loop statements	You can use `if`, `for`, and `while` statements in state actions. See Loops and Conditional Statements.	Loop ststaments are not supported. For conditional and loop patterns, use graphical functions instead. See Reuse Logic Patterns by Defining Graphical Functions.

Indexing and Data Handling

Functionality	MATLAB as the Action Language	C as the Action Language
Vector and matrix indexing	One-based indexing. For example, `A(1,2)`. See Operations for Vectors and Matrices in Stateflow.	Zero-based indexing. For example, `A[0][1]`. See Operations for Vectors and Matrices in Stateflow.
Index delimiters	Parenthesis with commas. For example, `A(1,2)`. See Operations for Vectors and Matrices in Stateflow.	Brackets. For example, `A[0][1]`. See Operations for Vectors and Matrices in Stateflow.
Variable-size data	You can modify variable-size chart data in state and transition actions. For more information, see Variable-Size Data in Charts That Use MATLAB as the Action Language.	You can modify variable-size chart data by using: MATLAB functions Simulink functions Truth tables that use MATLAB as the action language All computations with variable-size data must occur inside these functions, and not directly in states or transitions. For more information, see Variable-Size Data in Charts That Use C as the Action Language.
Scalar expansion	Not supported.	Supported. See Assign Values to All Elements.
String delimiters	Use double quotes (`"`...`"`) as delimiters. See Manage Textual Information by Using Strings.	Use double (`"`...`"`) or single quotes (`'`...`'`) as delimiters. See Manage Textual Information by Using Strings.
Complex data	Use the complex number notation `a + bi` or the `complex` operator. See Operations for Complex Data in Stateflow.	Use the `complex` operator. Complex number notation is not supported. See Operations for Complex Data in Stateflow.
Data type propagation	Follows MATLAB typing rules. For example, adding data of type `double` to data of type `int32` results in data of type `int32`.	Follows C typing rules. For example, adding data of type `double` to data of type `int32` results in data of type `double`.

Advanced Features and Code Generation

Functionality	MATLAB as the Action Language	C as the Action Language
Fixed-point constructs: The special assignment operator `:=` Context-sensitive constants such as `4.3C`	Not supported.	Supported. See Override Fixed-Point Promotion in C Charts and Fixed-Point Context-Sensitive Constants.
Explicit type cast operations	Use either the MATLAB type conversion function or the `cast` function. The `type` operator is not supported. See Type Cast Operations.	Use either the MATLAB type conversion function or the `cast` function with the `type` operator. See Type Cast Operations.
Dot notation for specifying states, local data, message, and local events inside MATLAB functions	Supported. See Identify Data by Using Dot Notation.	Not supported.
Structure parameters	Tunable and nontunable parameters are supported.	Only tunable parameters are supported.
Use of global `fimath` object	Supported.	Not supported.
Complex data	Use complex number notation `a + bi` or the `complex` operator. See Operations for Complex Data in Stateflow.	Use the `complex` operator. Complex number notation is not supported. See Operations for Complex Data in Stateflow.

Automatic Correction When Using MATLAB as the Action Language

Stateflow charts that use MATLAB as the action language automatically correct these C constructs to MATLAB syntax:

Increment and decrement operations such as a++ and a--. For example, a++ is changed to a = a+1.
Assignment operations such as a += b, a –= b, a *= b, and a /= b. For example, a += b is changed to a = a+b.
Evaluation operations such as a != b and !a. For example, a != b is changed to a ~= b.
Comment markers // and /* */ are changed to %.

To disable this preference, use the sfpref function:

sfpref(EnableLabelAutoCorrectionForMAL=false);

Guidelines for Using MATLAB as the Action Language

Follow these guidelines when coding in charts that use MATLAB as the action language.

Use one-based indexing for vectors and matrices

One-based indexing is consistent with MATLAB syntax. For more information, see Indexing Notation.

Use parentheses instead of brackets to index into vectors and matrices

This statement is valid:

a(2,5) = 0;

This statement is not valid:

a[2][5] = 0;

For more information, see Indexing Notation.

Use the MATLAB format for comments

Use % to specify comments in states and transitions for consistency with MATLAB. For example, the following comment is valid:

% This is a valid comment in the style of MATLAB

C style comments, such as // and /* */, are auto-corrected to use %.

Enclose transition actions with braces

This transition label contains a valid transition action:

E [x > 0] / {x = x+1;}

This transition label is incorrect, but is auto-corrected to the valid syntax.

E [x > 0] / x = x+1;

Do not use control flow logic in condition actions and transition actions

Control flow logic (such as if, switch, for, and while statements) is supported only in state actions. Use of control flow logic in condition actions or transition actions, result in a syntax error.

Do not declare global or persistent variables in state actions

The keywords global and persistent are not supported in state actions.

Assign an initial value to local and output data

When using MATLAB as the action language, data read without an initial value causes an error.

Include a type prefix for identifiers of enumerated values

The identifier TrafficColors.Red is valid, but Red is not.

To generate code from your model, use MATLAB language features supported for code generation

Otherwise, use coder.extrinsic to call unsupported functions, which gives the functionality that you want for simulation, but not in the generated code. For a list of supported features and functions, see Language, Function, and Object Support (Simulink).