Code Generation for Enumerations

Enumerations represent a fixed set of named values. Enumerations help make your MATLAB® code and generated C/C++ code more readable. For example, the generated code can test equality with code such as if (x == Red) instead of using strcmp. To generate C/C++ code, you must have Simulink® Coder™.

When you use enumerations in a MATLAB Function block, adhere to these restrictions:

Define Enumerations for MATLAB Function Blocks

You can define enumerations for MATLAB Function blocks in two ways:

  • To import an externally defined enumeration, use the Simulink.defineIntEnumType function. See Import Enumerations Defined Externally to MATLAB.

  • In a class definition file, define an enumerated type. For example:

    classdef PrimaryColors < Simulink.IntEnumType
        enumeration
            Red(1),
            Blue(2),
            Yellow(4)
        end
    end

If you define an enumerated type in a class definition file, the class must derive from one of these base types: Simulink.IntEnumType, int8, uint8, int16, uint16, or int32. Then, you can exchange enumerated data between MATLAB Function blocks and other Simulink blocks in a model.

If you use Simulink Coder to generate C/C++ code, you can use the enumeration class base type to control the size of an enumerated type in generated C/C++ code. You can:

  • Represent an enumerated type as a fixed-size integer that is portable to different targets.

  • Reduce memory usage.

  • Interface with legacy code.

  • Match company standards.

The base type determines the representation of the enumerated type in generated C/C++ code.

If the base type is Simulink.IntEnumType, the code generator produces a C enumeration type. Consider the following MATLAB enumerated type definition:

classdef LEDcolor < Simulink.IntEnumType
    enumeration
        GREEN(1),
        RED(2)
    end
end

This enumerated type definition results in the following C code:

typedef enum {
  GREEN = 1,                          
  RED
} LEDcolor;
For built-in integer base types, the code generator produces a typedef statement for the enumerated type and #define statements for the enumerated values. Consider the following MATLAB enumerated type definition:
classdef LEDcolor < int16
    enumeration
        GREEN(1),
        RED(2)
    end
 end
This enumerated type definition results in the following C code:
typedef int16_T LEDcolor;

#define GREEN                          ((LEDcolor)1)             
#define RED                            ((LEDcolor)2)

To customize the code generated for an enumerated type, see Customize Simulink Enumeration.

Allowed Operations on Enumerations

For code generation, you are restricted to the operations on enumerations listed in this table.

OperationExampleNotes

assignment operator: =

xon = LEDcolor.GREEN
xoff = LEDcolor.RED

relational operators: < > <= >= == ~=

xon == xoff

Code generation does not support using == or ~= to test equality between an enumeration member and a string array, a character array, or a cell array of character arrays.

cast operation

double(LEDcolor.RED)

conversion to character array or string

y = char(LEDcolor.RED);
y1 = cast(LEDcolor.RED,'char');
y2 = string(LEDcolor.RED);

  • You can convert only compile-time scalar valued enumerations. For example, this code runs in MATLAB, but produces an error in code generation:

    y2 = string(repmat(LEDcolor.RED,1,2));
  • The code generator preserves enumeration names when the conversion inputs are constants. For example, consider this enumerated type definition:

    classdef AnEnum < int32
        enumeration
            zero(0),
            two(2),
            otherTwo(2)
        end
    end

    Generated code produces "two" for

    y = string(AnEnum.two)
    and "otherTwo" for
    y = string(AnEnum.otherTwo)

indexing operation

m = [1 2]
n = LEDcolor(m)
p = n(LEDcolor.GREEN)

control flow statements: if, switch, while

if state == sysMode.ON
    led = LEDcolor.GREEN;
else
    led = LEDcolor.RED;
end

MATLAB Toolbox Functions That Support Enumerations

For code generation, you can use enumerations with these MATLAB toolbox functions:

Related Topics