How to compile Matlab class into C lib?

Question

The origin of this question is from here How to use "global static" variable in matlab function called in c.

I\'m trying to encapsulate the \"global variab

Answer 1

As noted by Alan, I was only suggesting using handle class as a container for your global variables (with the benefit that such an object would be passed by reference). The created object is not intended to be directly manipulated by your C++ code (it will be stored in the generic mxArray/mwArray C/C++ struct).

As far as I know, you cannot directly compile classdef-style MATLAB classes into proper C++ classes when building shared libraries using the MATLAB Compiler. It only supports building regular functions. You could create functional interfaces to MATLAB class member methods, but that's a different story...

Perhaps a complete example would help illustrate the idea I had in mind. First lets define the code on the MATLAB side:

GlobalData.m

This is the handle class used to store the global vars.

classdef GlobalData < handle
    %GLOBALDATA  Handle class to encapsulate all global state data.
    %
    % Note that we are not taking advantage of any object-oriented programming
    % concept in this code. This class acts only as a container for publicly
    % accessible properties for the otherwise global variables.
    %
    % To manipulate these globals from C++, you should create the class API
    % as normal MATLAB functions to be compiled and exposed as regular C
    % functions by the shared library.
    % For example: create(), get(), set(), ...
    %
    % The reason we use a handle-class instead of regular variables/structs
    % is that handle-class objects get passed by reference.
    %

    properties
        val
    end
end

create_globals.m

A wrapper function that acts as a constructor to the above class

function globals = create_globals()
    %CREATE_GLOBALS  Instantiate and return global state

    globals = GlobalData();
    globals.val = 2;
end

fcn_add.m, fcn_times.m

MATLAB functions to be exposed as C++ functions

function out = fcn_add(globals, in)
    % receives array, and return "input+val" (where val is global)

    out = in + globals.val;
end

function out = fcn_times(globals, in)
    % receives array, and return "input*val" (where val is global)

    out = in .* globals.val;
end

With the above files stored in current directory, lets build the C++ shared library using the MATLAB Compiler:

>> mkdir out
>> mcc -W cpplib:libfoo -T link:lib -N -v -d ./out create_globals.m fcn_add.m fcn_times.m

You should expect the following generated files among others (I'm on a Windows machine):

./out/libfoo.h
./out/libfoo.dll
./out/libfoo.lib

Next, we could create a sample C++ program to test the library:

main.cpp

// Sample program that calls a C++ shared library created using
// the MATLAB Compiler.

#include 
using namespace std;

// include library header generated by MATLAB Compiler
#include "libfoo.h"

int run_main(int argc, char **argv)
{
    // initialize MCR
    if (!mclInitializeApplication(NULL,0)) {
        cerr << "Failed to init MCR" << endl;
        return -1;
    }

    // initialize our library
    if( !libfooInitialize() ) {
        cerr << "Failed to init library" << endl;
        return -1;
    }

    try {
        // create global variables
        mwArray globals;
        create_globals(1, globals);

        // create input array
        double data[] = {1,2,3,4,5,6,7,8,9};
        mwArray in(3, 3, mxDOUBLE_CLASS, mxREAL);
        in.SetData(data, 9);

        // create output array, and call library functions
        mwArray out;
        fcn_add(1, out, globals, in);
        cout << "Added matrix:\n" << out << endl;
        fcn_times(1, out, globals, in);
        cout << "Multiplied matrix:\n" << out << endl;
    } catch (const mwException& e) {
        cerr << e.what() << endl;
        return -1;
    } catch (...) {
        cerr << "Unexpected error thrown" << endl;
        return -1;
    }

    // destruct our library
    libfooTerminate();

    // shutdown MCR
    mclTerminateApplication();

    return 0;
}

int main()
{
    mclmcrInitialize();
    return mclRunMain((mclMainFcnType)run_main, 0, NULL);
}

Lets build the standalone program:

>> mbuild -I./out main.cpp ./out/libfoo.lib -outdir ./out

And finally run the executable:

>> cd out
>> !main
Added matrix: 
     3     6     9 
     4     7    10 
     5     8    11 
Multiplied matrix: 
     2     8    14 
     4    10    16 
     6    12    18 

HTH