Mex building from C++ DLL

Hi,

I have a C++ DLL and its header file. I'm trying to build a MEX function for each function in the DLL, and one of the functions has the following signature:

% // This is from the C++ header file

int myFunc( const char * const Input1, SomeStructType * Output1, int & Output2);
{
    ...
}

When I try to build a MEX in defining the inputs in my MATLAB workspace and then I run this command:

myFuncReturnValue = coder.ceval('myFunc', coder.ref(Input1), coder.ref(Output1), ***???***)

The error i get is:

...error C2664: 'int myFunc( const char * const Input1, SomeStructType * Output1, int & Output2)': cannot convert argument 3 from 'int16_t' to 'int &'...

I couldn't find any help defining 'int &' as a MATLAB datatype so i can't pass it into the MEX builder.

Can anyone help me with this issue please?

Thanks,

Tamir

Answer 1

[Mukund Sankaran]

Hi Tamir,

Unfortunately, calling a C++ function that has a reference parameter in its signature is not supported in MATLAB Coder as of MATLAB R2020b. We've made an internal note of your request so we can look at lifting that limitation in the future. Meanwhile, as a workaround, the best you can do is to create a wrapper C++ function that takes a pointer, which in turn calls the function that takes the reference, as I've shown in the following simple example:

myFunc.hpp

int myFunc(int& out);

myFunc.cpp

#include "myFunc.hpp"

int myFunc(int& out)
{
    out = 2;
    return 5;
}

myFuncWrapper.hpp

#include "myFunc.hpp"

inline int myFuncWrapper(int* out) {
    return myFunc(*out);
};

callMyFuncWrapper.m

function y = callMyFuncWrapper  %#codegen
    y = int32(0);
    if coder.target('MATLAB')
        % Executing in MATLAB, call MATLAB equivalent of
        % C function myFuncWrapper
        y = int32(5 + 2);
    else
        % Executing in generated code, call C function myFuncWrapper
        coder.updateBuildInfo('addSourceFiles','myFunc.cpp');
        coder.cinclude('myFuncWrapper.hpp');
        in = int32(0);
        y = coder.ceval('myFuncWrapper', coder.ref(in));
        y = y + in;
    end
end

Call codegen

>> codegen callMyFuncWrapper -report -lang:c++

Hope this helps!

[Tamir Vizel]

I'll try it soon, Thank you :)