How to import external c types with namespaces?

Question

Tobias Pape 2022-6-22

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1745525-how-to-import-external-c-types-with-namespaces

编辑： Yao Ren 2025-10-15，16:48

在 MATLAB Online 中打开

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.

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Answer 1

Nitanshu 2022-6-28

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Hi Tobias,

You can take help from this Matlab documentation.

Hope it helps!

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Tobias Pape 2022-7-4

Hi Nitanshu,

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

The documentation does not explain why namespaces will be ignored.

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Answer 2

Yao Ren 2023-5-9

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

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Yao Ren 2024-1-12

编辑：Yao Ren 2024-1-12

在 MATLAB Online 中打开

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

Yao Ren 2024-1-18

编辑：Yao Ren 2024-1-18

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.

Yao Ren 2025-1-22

Hi @Marcus,

Thanks for reporting these issues! Please see my comments below:

Error: "modelname.rtw Line: 601 Column: 17 syntax error".

This appears to be an ERT code generation issue. We hope it will be resolved in the general release.

Slow Import to .sldd File.

I attempted to reproduce the import speed issue and compared it with version 24b. In my tests, importing to the DesignData section of the data dictionary is twice as slow in version 25a. Importing to the ArchitecturalData section is five times slower compared to importing to the DesignData section in 24b. However, this isn't a direct comparison since the ArchitecturalData section is a new feature in 25a. Are you experiencing similar slowdowns? Note that keeping the Data Dictionary open during import can increase the time, particularly when the ArchitecturalData section is visible. The UI rendering during type creation can be time-consuming. We will conduct profiling and aim to optimize the speed for the general release.

Error Message: "because there are multiple types of the same name under different namespaces. Specify only one type using 'Names' option with the namespace-qualified type name."

If you have two types, "ComponentA::Settings_t" and "ComponentB::Settings_t", in header files, Simulink can only have one Simulink Type named "Settings_t" in scope at a time. A single data dictionary can contain only one "Settings_t" type, which is why this error occurs. You can import only one of the two types by using 'Name', 'ComponentB::Settings_t' to remove the ambiguity. This is a known limitation not addressed in 25a. Simulink has plan to introduce native namespaces for modeling, allowing one data dictionary to hold two types named "Settings_t" in different Simulink namespaces.

Question: In your use case, do you need to use both "ComponentA::Settings_t" and "ComponentB::Settings_t" types in one model?

Enum Class with Element Named "all" Causes Import Crash.

We will reproduce this issue and fix it in the general release.

Marcus 2025-1-23

编辑：Marcus 2025-1-23

Hi @Yao Ren

Regarding Slow Import to .sldd file i got the following metrics

2025a

Simulink.importExternalCTypes('myHeader.h', 'Language', 'C++', 'DataDictionary', 'myDictionary.sldd', 'DataDictionarySection','ArchitecturalData');

Elapsed time: 104,36 seconds

2025a

Simulink.importExternalCTypes('myHeader.h', 'Language', 'C++');

Elapsed time: 2.16 seconds

2024a

Simulink.importExternalCTypes('myHeader.h', 'Language', 'C++');

Elapsed time: 1.91 seconds

As you can see it is a magnitude of 50 times the time of a standard importExternalCTypes which will make this tool tedious to use.

Regarding Error Message: "because there are multiple types of the same name under different namespaces. Specify only one type using 'Names' option with the namespace-qualified type name."

Yes right now we need to do workarounds for handling this. But from our side i would say that simluink handles this correctly is a requirement to make the most of c++ as the generation target language.

Tomorrow i will report how the import of mutiple headers with the same enumerations header file test is going.

Marcus 2025-5-27

Hi Yao Ren,

have you abandoned the SLDD solution?

Your suggestion feels like a short-term fix and not incorporation how c++ works. My suggestion is the following.

Same example there are two C++ types "ComponentA::Settings_t" and "ComponentB::Settings_t". Simulink.importExternalCTypes() imports both as Simulink types. as follows.

namespace ComponentA %Or ComponentB

classdef Settings_t < Simulink.IntEnumType

% MATLAB enumeration class definition generated from template

enumeration

SettingA(0),

SettingB(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 = Settings_t.SettingA;

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 = 'Enums.h';

end

function flag = addClassNameToEnumNames()

% ADDCLASSNAMETOENUMNAMES Indicate whether code generator applies the class name as a prefix

% to the enumeration.

flag = false;

end

The namespace as in c++ is optional when creating a classdef and is only present if the user wants it or namespace is present in the c++ file which is imported.

The usage in simulink is then ComponentA.Settings_t.SettingA or as you suggested ComponentA__Settings_t.SettingA. With this no extra include is needed and matlab supports how c++ is intended to be used. Also when we generate the namespace is already known so it will then become ComponentA::Settings_t

Note that if this is used the character length of only 63 characters must be expanded in my opinion. Otherwise, we will get allot of issues when namespace is added into simulink.

Marcus 2025-10-10，8:39

@Yao Ren Ping see above

Yao Ren 2025-10-15，16:47

编辑：Yao Ren 2025-10-15，16:48

@Marcus Please contact MathWorks support to open a case. We can go from there, for example a Webex or MSTeams meeting to disucss the requirements.

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How to import external c types with namespaces?

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