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Pass Enumerations to MATLAB From C++

To call MATLAB® functions that require MATLAB enumeration members as inputs, define the enumeration member as a matlab::data::EnumArray. Use matlab::data::ArrayFactory to create the enumeration array. The matlab::data::EnumArray contains the MATLAB class name and one or more enumeration members. You can also pass the array as a variable to the MATLAB workspace using MATLABEngine::setVariable.

Note

To pass a matlab::data::EnumArray to MATLAB, the named MATLAB class must exist and be on the MATLAB path.

Suppose that you define the following TextString in MATLAB. This class defines a property that is typed as a specific enumeration class named TextColor. The TextString class constructor takes two input arguments:

  • Str — A 1-by-n char array

  • Color — An enumeration member of the TextColor class.

classdef TextString
    properties
        Str(1,:) char
        Color TextColor
    end
    methods
        function obj = TextString(str,color)
            if nargin == 2
                obj.Str = str;
                obj.Color = color;
            end
        end
    end
end

Here is how to define the MATLAB TextColor enumeration class.

classdef TextColor
   enumeration
       Red
       Green
       Blue
   end
end

This MATLAB statement creates a TextString object by passing a character vector and an enumeration member to the class constructor.

T = TextString('Any text string',TextColor.Blue);

The following sample code creates a MATLAB TextString object and displays the property values. To create the TextString object:

  • Define a matlab::data::CharArray for the MATLAB character vector argument.

  • Define a matlab::data::EnumArray for the MATLAB TextColor.Blue enumeration argument.

  • Pass the argument vector to MATLABEngine::feval.

  • Get the property values using MATLABEngine::getProperty and display the values.

Note

This example requires you to define the MATLAB TextString and TextColor classes described here. These classes must be on the path of the shared MATLAB session used by this example.

#include "MatlabDataArray.hpp"
#include "MatlabEngine.hpp"
#include <iostream>

void enumArray() {

    using namespace matlab::engine;

    // Connect to named shared MATLAB session started as:
    // matlab -r "matlab.engine.shareEngine('myMatlabEngine')"
  String session(u"myMatlabEngine");
  std::unique_ptr<MATLABEngine> matlabPtr = connectMATLAB(session);

    // Create MATLAB data array factory
    matlab::data::ArrayFactory factory;

    // Create enumeration array
    auto enumColor = factory.createEnumArray({ 1,1 }, "TextColor", { "Blue" });

    // Create argument vector
    std::vector<matlab::data::Array> args({
        factory.createCharArray("Any text string"),
        enumColor});

    // Call MATLAB TextString to create object
    matlab::data::Array T = matlabPtr->feval(u"TextString", args);

    // Get the value of the Str property
    matlab::data::CharArray c = matlabPtr->getProperty(T, u"Str");
    std::cout << "Str property value: " << c.toAscii() << std::endl;

    // Get the value of the Color property
    matlab::data::EnumArray col = matlabPtr->getProperty(T, u"Color");
    std::cout << "Color property class: " << col.getClassName() << std::endl;
    std::cout << "Color property value: " << std::string(col[0]) << std::endl;
}

Here is the program output.

Str property value: Any text string
Color property class: TextColor
Color property value: Blue

For information on how to setup and build C++ engine programs, see Build C++ Engine Programs.

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