C++ DLL (callable from VBA and receiving Range data)

[MirkoP]

I am getting sick to figure out how to build a .dll to call in VBA and make possible my customized formulae. I want to make a .dll because of performance timing and so I started to study C++. As every project I've begun face issues after issues specially with the Range object to pass from VBA to my .dll.

Brief over my project: with Visual Studio 2019 I built a project with one file .cpp and another .def to EXPORT my functions.

Everything went right when I have to pass from VBA simple double arguments, but when I should pass a Range of Cells, I started to face seriuos annoing problem which block my project.

Actually, I read too many forums and also section of Dalton's books to handle my issues, but anything it's really clear to me.

I found something which talks about COM and API C, other about "ExportImport.c pp", SAFEARRAY and VARIANT type (the latter: I could figure out how to pass arguments from VBA to C++ dll, but still don't understand how to achive and use single element and specially return them).

If it's not too annoing for some of you, I would like a specific description of what to do in this case.

Thank you

Here my project which is called square and has two functions square and my _array:

.cpp file

#include <iostream>
#include <cmath>
#include <OAIdl.h>
 
double __stdcall square(double& x)
{
    return x * 2;
}
 
VARIANT __stdcall my_array(VARIANT *p)
{
    //my statements and operation on the array (Range received from VBA)
}
 

.def file

LIBRARY "square"
EXPORTS 
square @1
my_array @2
 

SPECIALLY, I WOULD UNDERSTAND HOW TO PASS A RANGE FROM VBA TO THE FUNCTION "my_array" AND HOW TO MANGE EVERY ELEMENT OF THE RANGE I PASSED