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VBA runtime error 453 with declare statement [duplicate]

In VS C/C++ you could use extern "C" __declspec(dllexport) -function declaration-.
How do I accomplish this in a C# dll? Is there C# code equivalent to the above code?
Edit: More info
I am trying to create an add in for Notepad++ and I want to use C#, but the common way I've seen so far is to use legacy C++ code with the above call to export a few of the functions that Notepad++ expects to import and call. There is an example app using C#, but this still requires a loader DLL, which I assume from the comments/answers below is the only way for C#.

Unmanaged Exports =>
https://sites.google.com/site/robertgiesecke/Home/uploads/unmanagedexports
DLLExport => https://github.com/3F/DllExport
How does it work?
Create a new classlibrary or proceed with an existing one.
Then add the UnmanagedExports Nuget package.
This is pretty much all setup that is required.
Now you can write any kind of static method, decorate it with [DllExport] and use it from native code.
It works just like DllImport, so you can customize the marshalling of parameters/result with MarshalAsAttribute.
During compilation, my task will modify the IL to add the required exports...

I've seen people do this before, but it required ildasm, adding the MSIL .export directive, and then reassembling. A program named dll_tool can do these steps for you.
If you want to build a mixed-mode DLL with both native and managed exports, you should be using C++/CLI, which is specially designed for this purpose.

Yes, it is possible to export functions from a C# dll in much the same way that C++ does it! You need a little help from an add-in Unmanaged Exports (DllExport for .Net) that facilitates this process, or from a similar method such as Exporting functions in C#/VB.NET to native code.
Please see Code to Export C# DLL to Metatrader Build 600+ for a working example using Robert Giesecke's C# Project Template for Unmanaged Exports to export a C# dll to a legacy application (Metatrader) that has a great deal of similarity to C++.
Additionally, you might find Native and .NET Interopability interesting though it is mostly geared toward accessing native code from within .NET rather than the other way around.

No, you cannot do that in the same sense as you do in C and C++.
But you can create COM API to achieve that which then you can use in C and C++ code.
See these articles
C# Classes as COM Objects
Calling Managed .NET C# COM Objects from Unmanaged C++ Code
COM Interop Part 1: C# Client Tutorial

C# and Delphi integration

Currently we have couple projects that are written in Delphi 6. Because of specific components that use in these projects (components also written in Delphi 6) it is not easy to convert it in newer version.
As I prefer .NET development and our new products are developed in .NET, I would like to develop new functionalities using these technologies. C# will be programming language.
My question is: How to integrate new functionalities developed in C# with current code in Delphi? Is this good idea at all and what can be possible issues? If someone have similar experience it would be to hear advantages and disadvantages.
I heard for integration in way to develop .dll with C# and use it from Delphi code.
TnX in advance!
Nemanja

You can use COM (ActiveX) both ways.
So Yes, you can make a DLL in C# and mark it as COM-visible and import it into Delphi.
But you cannot use simple (not COM) DLLs this way.

My first port of call would probably be looking into WCF (written in C#) and have Delphi talk to it.
The dll is not a bad idea, but I just think putting it in WCF is more scalable + portable.

COM would probably be my choice. However, if for some reason you wanted to avoid COM you could take a look at the very nifty Unmanaged Exports by Robert Giesecke.
Unmanaged Exports is an MSBuild task that essentially allows you to export static functions from your .Net assemblies to be consumed as ordinary native DLL exports.

You may want to check out Hydra from RemObjects. It permits native and managed code to be used in the same application.
http://www.remobjects.com/hydra/default.aspx

Creating COM object from C++?

I want to create a dll from a C++ code and the use it in C#. Is there a solution of creating COM object from C++ ?
I don't want to use System.Runtime.InteropServices.
Many thanks

Of course that you can write COM+ objects with C++. Here's a tutorial.

You can write COM directly (see #Darin Dimitrov's answer), but you can also use ATL. My favorite solution to expose C++ code to C# (without COM though) is to use C++/CLI.

There are 3 ways to go about it.
1) Use PInvoke from C# to call into native methods.
2) Use C++-CLI to create a layer that exposes native functionality to C#. This is my recommended approach performance wise.
3) Write the C++ dll as a COM object and access from C#. Requires COM knowledge and hence developement cost.

you can use ATL , it too easy and you just have to register the dll . after that you can use it in all c# programms

how to use C dll headers library in c#

I am very new to C#, and i am trying to use a help package for my project.
The package is written in c and has
1) /bin/ several .dll files
2) /include/ has a header file
3) /lib/msvc/ .lib file
my question is how can i use those files in my C# WPF project?
i know there is no "#include" in C#, and the .dll can not be imported by adding to the project's reference. so how can i do it in C#?
Thanks

You need to add a series of C# Platform Invocation method definitions. This tells C# how to call into the .dll, and use the C API directly.
The header and library files are completely unused.

Just adding to the answers, you may want to take a look in this blog post. It has a link to a Visual Studio addin that can generate P/Invoke signatures from your headers.
Best

You might find managed C++ useful. You can write a managed C++ library that uses the header files and the .lib directly, and wraps them with a set of .NET classes to be used by C#.

You need to use pInvoke
http://msdn.microsoft.com/en-us/library/aa288468%28VS.71%29.aspx

There are a lot of ways to do this "interop" - I once did a talk called "head spinning interop". The key is the structure of your native DLL. Since you say it's in C, the chances are it's in perfect shape to be used with PInvoke, which works best with C functions or C-style functions in C++. The other answers have excellent pointers to the syntax and some help to get your function (and the parameters it takes) declared on the C# side.
The other two main options are a C++/CLI wrapper, a good choice when the functions take a lot of complicated types, or COM, which would almost certainly require you to change the native code so is not a good fit in this situation.

Creating C++ Dll, and call it from C#

In my project I got a device which comes with C++ Sample codes. The codes are ok and the device is working as expected.
But I need it to talk with my C# interface because all other devices are currently using C# interface.
So I am planning to create a DLL Wrapper for the driver. I will create a C++ Library of my own (from source code with proper interface) and Call this C++ Library from C# using DLLImport (just call my interfaces there.).
I am pretty sure it can be done this way, but I have never created a C++ Library and used it from C# yet. So, can anyone refer me to some tutorial that goes with my problem?
I am using C++/C# int VS.NET 2008.
Regards,
Maksud

Have a look at
using a class defined in a c++ dll in c# code

Another useful tool you have at your disposal is C++ CLI.
You can use C++ CLI to create an intermediate library - one that exposes managed classes but runs unmanaged C++ code. You can actually mix managed and unmanaged C++ in the same DLL.
The unmanaged portion can accesses the unmanaged DLLs without having to use the PInvoke functions.
Your C# code can access the managed classes in this intermediate library.

Depending on the DLL and what you need to do you may not need to create a wrapper directly. You might be able to get away with P/Invoke for the functions. You will need to evaluate your specific needs and what is already available in the libraries/code provided.

For anyone who comes to this question and are looking for answers, you may want to try xInterop NGen++ , a C# wrapper generator for native C++ DLL, which has been just released to the public, the tool can generate C# wrapper for native C++ DLL automatically and instantly by using advanced P/Invoke technologies. Check out the current version and a free version will be out soon.
(I am the author of the tool)