MATLAB: Matlab Coder – Create DLL

dllmatlab coder

As an example here is a function, that I want to compiler through Matlab coder in a DLL:
function [C] = Test(A,B) %#codegen
C=A+B;
end
Compiling this function and loading the DLL with "loadlibrary" I can see the required calling convention using libfunctionsview as expected: Return Type Name Arguments double Test (double, double)
Instead, if I have a function with two outputs:
function [C,D] = Test(A,B) %#codegen
C=A+B; D=A-B;
end
The calling convention is the following:
Return Type Name Arguments [doublePtr, doublePtr] Test (double, double, doublePtr, doublePtr)
Why the two additional arguments "… doublePtr, doublePtr)"? I need to avoid this and have a calling convention like this: Return Type Name Arguments [double, double] Test (double, double)

Best Answer

When arguments are passed by pointer, loadlibrary creates extra output arguments for them. The third bullet at:
http://www.mathworks.com/help/matlab/matlab_external/passing-arguments-to-shared-library-functions.html#f48607
describes this more.
MATLAB Coder will generate a C function with a signature like:
void Test(double A, double B, double *C, double *D);
where the arguments C and D hold the return values after the call. C does not support returning multiple arguments like MATLAB, so multiple return values must be accomplished by using output reference arguments.
If you are going to use the code in MATLAB, generating a MEX function would make calling the generated code simpler. The generated MEX would be invoked as any other MATLAB function.
You could also generate a MEX function that calls your generated DLL using coder.ceval. There is an example in the documentation that shows how to do this.
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