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.

For code generation, when you use enumerations, adhere to these restrictions:

Calls to methods of enumeration classes are not supported.
Passing strings or character vectors to constructors of enumerations is not supported.
The enumeration class must derive from one of these base types: int8, uint8, int16, uint16, or int32. See Define Enumerations for Code Generation.
You can use only a limited set of operations on enumerations. See Allowed Operations on Enumerations.
Use enumerations with functions that support enumerated types for code generation. See MATLAB Toolbox Functions That Support Enumerations.

Define Enumerations for Code Generation

For code generation, the enumeration class must derive from one of these base types: int8, uint8, int16, uint16, or int32. For example:

classdef PrimaryColors < int32
    enumeration
        Red(1),
        Blue(2),
        Yellow(4)
    end
end

You can use the 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.

Representation of Enumerated Type in Generated Code

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

If the base type is the native integer type for the target platform (for example, int32), the code generator produces a C/C++ enumerated type. Consider this MATLAB enumerated type definition:

classdef LEDcolor < int32
    enumeration
        GREEN(1),
        RED(2)
    end
end

This enumerated type definition results in the following C/C++ code:

enum LEDcolor
{
    GREEN = 1,
    RED
};

typedef enum LEDcolor LEDcolor;

For built-in integer base types that are different from the native integer type for the target platform:

If you generate C code, the code generator produces a typedef statement for the enumerated type and #define statements for the enumerated values. Consider this MATLAB enumerated type definition:
```
classdef LEDcolor < int16
    enumeration
        GREEN(1),
        RED(2)
    end
    
end
```
The enumerated type definition produces this C code:
```
typedef short LEDcolor;
#define GREEN ((LEDcolor)1)
#define RED ((LEDcolor)2)
```
If you generate C++ code, the enumeration members are converted to constants. These constants belong to the namespace that contains the enumeration type definition in the generated C++ code.
For example, suppose that you place this MATLAB enumerated type definition inside the package pkg:
```
classdef LEDcolor < int16
    enumeration
        GREEN(1),
        RED(2)
    end
    
end
```
The default behavior of the code generator is to convert MATLAB packages to C++ namespaces. The generated C++ code is placed inside the namespace pkg:
```
namespace pkg {
typedef short LEDcolor;

// enum pkg_LEDcolor
const LEDcolor GREEN{1};
const LEDcolor RED{2};

}
```

The C/C++ type in the typedef statement depends on:

The integer sizes defined for the production hardware in the hardware implementation object or the project settings. See coder.HardwareImplementation.
The setting that determines the use of built-in C types or MathWorks^® typedefs in the generated code. See Specify Data Types Used in Generated Code and Mapping MATLAB Types to Types in Generated Code.

Allowed Operations on Enumerations

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

Operation	Example	Notes
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	—