How to import external c types with namespaces?

I try to import external c header files to my simulink model.

I am using the function ImportExternalCTypes() (Matlab2021b) to import the header file.

Call of the function:

Simulink.importExternalCTypes('test.h', 'Language', 'C++', 'Overwrite', 'on', 'DataDictionary', 'Types.sldd')

Content of the header file test.h:

#include <string>
#include <vector>
#include <stdexcept>

namespace System {
  namespace Command {
    enum Type {
      On,
      Off
    };
  }
  
enum class Subystem {
    Stop,
    Start
}; 

The enumeration within the namespace will be ignored.

Only the enumeration Subystem will be added to the Data Dictionary.

Is there a wag that Matlab recognizes the Enumeration within the namespace?

I get an auto generated header file with the namespaces. All Enumerations are defined within namespaces in the original header file.

Answer 1

[Nitanshu]

Hi Tobias,

You can take help from this Matlab documentation.

Hope it helps!

[Tobias Pape]

Hi Nitanshu,

thank you for your answer. I already read the documentation.

The documentation does not explain why namespaces will be ignored.

Answer 2

[Yao Ren]

Importing struct and enum types inside of C++ namespaces is supported in R2023a. Please upgrade to MATLAB R2023a.

[Neil Bajaj]

Is there a page showing how to do this?

[Brandon]

Apparently not?

@Yao Ren???

[Yao Ren]

The documentation page for Simulink.importExternalCTypes is listed below

Generate Simulink representations of custom data types defined by C or C++ code - MATLAB Simulink.importExternalCTypes (mathworks.com)

It does not specifically explain how to import types under C++ namespaces as the workflow should just work using the documented options. (Types under namespaces not being imported was a limitation prior to release R2023a)

To try it, please use MATLAB release R2023a or later.

1) Copy paste the following sample C++ header code into a file named "test.h". Notice there are two enum types "Subystem", and "Type", which is inside of namespace "System::Command::"

#include <string>
#include <vector>
#include <stdexcept>
namespace System {
  namespace Command {
    enum Type {
      On,
      Off
    };
  }
}
  
enum class Subystem {
    Stop,
    Start
}; 

2) In MATLAB command windows, run the following command. Make sure you have a mex compiler set up for C++ by running command "mex -setup C++" prior to running "Simulink.importExternalCTypes"

>> Simulink.importExternalCTypes('test.h', 'Language', 'C++', 'DataDictionary', 'Types.sldd')

3) Notice a Simulink Data Dictionary file "Types.sldd" is created in current directory. Double click the sldd file to open it up and observe enum types "Type" and "Subystem" imported under "Types > Design Data" section.

4) If you'd like the enum types imported as enum class M files in current folder. Run the command without "DataDictionary" option

>> Simulink.importExternalCTypes('test.h', 'Language', 'C++')

5) Check two enum class M files are generated, "Type.m" and "Subystem.m". The content of "Type.m" is pasted here.

classdef Type < Simulink.IntEnumType
    % MATLAB enumeration class definition generated from template
    
    enumeration
        On(0),
        Off(1)
    end

    methods (Static)
        
        function defaultValue = getDefaultValue()
            % GETDEFAULTVALUE  Returns the default enumerated value.
            %   If this method is not defined, the first enumeration is used.
            defaultValue = Type.On;
        end

        function dScope = getDataScope()
            % GETDATASCOPE  Specifies whether the data type definition should be imported from,
            %               or exported to, a header file during code generation.
            dScope = 'Imported';
        end

        function desc = getDescription()
            % GETDESCRIPTION  Returns a description of the enumeration.
            desc = '';
        end
        
        function headerFile = getHeaderFile()
            % GETHEADERFILE  Specifies the name of a header file. 
            headerFile = 'test.h';
        end
        
        function flag = addClassNameToEnumNames()
            % ADDCLASSNAMETOENUMNAMES  Indicate whether code generator applies the class name as a prefix
            %                          to the enumeration.
            flag = false;
        end

    end

end

[Brandon]

@Yao Ren

There are two issues here.

1) Importing C++ enums that reside inside namespace (which I can confirm does work fine in R2023a)

2) Generating code from a Simulink model that uses this enum. This does not seem to work (in R2023a at least) because the generated code does not prepend the enum types or enum values with the original namespace. Indeed the "Type.m" matlab enum file you show above does contain any information about the original namespace, so there's no way for the generated code to know that it should be namespacing that enum. Ergo, this seem like a broken workflow in matlab.

[Yao Ren]

Hi @Brandon,

Regarding issue 2), we are currently developing a feature that will introduce the concept of "namespace" to Simulink modeling. With this feature, the function Simulink.importExternalCTypes() will be capable of importing a C data type as a Simulink type into the Simulink Data Dictionary (.sldd), organizing them under the appropriate namespaces. This will ensure that model code generation can properly recognize and utilize these namespaces.

In the meantime, for users of R2023a or later, there is a workaround that allows the generation of C++ code from a model in such a way that the generated code respects the namespaces of the imported C++ data types.

Please follow the steps below to apply this workaround:

1) Navigate to model's "Configuration Parameters" and then to the "Simulation Target" section. Here, you need to include the C++ code headers containing the types in the "Include headers" field. It's important to ensure that the "Include directories" field lists all the directories needed to search for any header files that are directly or indirectly included. If all headers are located in the current working directory, this field can be left empty, as the current directory is always included in the search path by default. Note that the "Include directories" can be specified as relative paths to the location of the model file. The screenshot below demonstrates how to enter the include headers, using the previous "test.h" example as a reference.

The model will parse the header files specified in step 1) and recognize all the types, such as "enum Type" from our example, noting that it is encapsulated within the "System::Command::" namespace.

2) Ensure that the Code Generation "Language" is set to "C++". If you are importing enum class types, also make sure that the "Language standard" is set to "C++11 (ISO)".

3) Proceed with generating the code for your model. The code generation process will be able to match the imported Simulink.EnumType "Type" with the C++ data type "System::Command::Type" found in "test.h". Consequently, it will generate the correct code that includes namespaces for type references.

By following these steps, you should be able to generate C++ code that honors the namespaces of imported C++ data types, even before the new feature is officially released.

[Fe]

Hi @Yao Ren,

thanks for the workaround explanation! Are there any updates on the official fix that does not require the workaround?

[Marcus]

Hello @Yao Ren, im also interested when this till be incoperated without the workaround. Any updates?

[Yao Ren]

Hello @Fe @Marcus, we may be able to support this workflow in R2025a release (roughly 6 months from now). It requires C/C++ types being imported into a Simulink Data Dictionary (SLDD). To use these imported types in a model, model has to link to the SLDD. Is this requirement ok with you? If you have additional requirements, please post them here. Thanks!

[Marcus]

That works for us. We can support and test this feature in the prerelease if you need any feedback on this new feature.