Using the EnergyPlusAPI with C#

[tkdogan]

Is there any documentation on how to use the EnergyPlus API with .NET C#? This article states that there should be an "EnergyPlusWrapper.dll" but I am having trouble finding that.

[Myoldmopar]

That article was made by a user and is littered with mistakes. It also mentions we package a .jar file for EnergyPlus, which we do not. The example code is also woefully wrong. It's not to say that some of the ideas in the article are bad, but it appears to have been almost entirely generated artificially. I've reached out to them to ask them about it; it is already causing confusion as users see it on LinkedIn.

[tkdogan]

Thanks for the quick clarification. So no support for C# at this point?

[Myoldmopar]

Not directly, although in years past I've called unmanaged libraries from .Net (VB.Net at the time), and it was fine. It's possible you could just add a dependency on our raw C API and make use of EnergyPlus as a library.

[tkdogan]

When I try what you suggest, I get an error. Could you share some more pointers on how you did this?

[Myoldmopar]

(Finds code in his archive from 2007)

I had to load up the unmanaged DLL using raw Windows DLL function calls, such as:

<DllImport("kernel32.dll")> Public Shared Function LoadLibrary(ByVal moduleName as String) As IntPtr

Once the DLL was found, I would similarly use GetProcAddress to find the callable functions inside the DLL. I could then register one of my VB.Net functions as a callback using Marshal.GetDelegateForFunctionPointer(AddressFromGetProcAddress, GetType(CallbackType))

Then by executing EnergyPlus' main function as a DLL, I could do operations in the callback. Don't forget to FreeDLL!

Now, this was calling a Fortran DLL from VB.Net, in 2007. Things have gotten better since then. I would imagine you can find info about calling C from C# from a quick web search. Here's what ChatGPT says lol:

// mydll.h
#ifdef MYDLL_EXPORTS
#define MYDLL_API __declspec(dllexport)
#else
#define MYDLL_API __declspec(dllimport)
#endif
MYDLL_API int Add(int a, int b);

// mydll.c
#include "mydll.h"
int Add(int a, int b) {
    return a + b;
}

// C#
using System;
using System.Runtime.InteropServices;

class Program {
    [DllImport("mydll.dll", CallingConvention = CallingConvention.Cdecl)]
    public static extern int Add(int a, int b);

    static void Main() {
        int result = Add(5, 7);
        Console.WriteLine("Result: " + result);
    }
}