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Automatically perform C# wrapping of a C++ library

I've done a bit of research around this before posting but I couldn't find a direct answer specific to my environment.
I have a third party library written in C++. I have access to the .dll, .lib and .h headers of the library.
I'd like to wrap the library for use in C# using p/invoke. I'd like to know what options I have in terms of doing this and maintaining it. My hope here is that with the .h headers I can utilize some application to automatically provide the wrapper code.
I'm interested in all kinds of solutions including commercial software solutions and any pitfalls of trying to automatically manage the wrapper code.

You could try SWIG which is free. You may be able to script it to run automatically as part of a build process.
Personally I'd just write some wrappers using [DllImport]. Do you really need to access everything in the C++ library from C#? Often I've found you really only need to call a few functions, and the simplicity of dllimport is great

My hope here is that with the .h headers I can utilize some application to automatically provide the wrapper code.
It would be lovely if this were possible, but it is not. It is not possible because the header file does not contain enough information to determine how to marshal parameters. For instance, consider this declaration:
void foo(int *x);
What is x? Its type is int*, pointer to int. But is it a pointer to a single int value, or is it an array of int? You simply cannot tell from the header file. You need to read the documentation.
And what about data flow. Is the information flowing into the native code, or out of it, or in both directions? Again, that detail cannot be expressed a header file.
Now, there are various annotation conventions that can help with this. Essentially these are macros that evaluate to nothing that can be read by a tool and so help with conversion. You see Win32 API functions annotated with _In_, _In_Opt_, etc. These can help, but only the very simplest of libraries can be automatically translated into p/invoke declarations.
Now, if you are prepared to add extra annotation to the raw header files then you might have a chance. It is certainly possible that existing tools exist that will do a good job so long as you express the missing information in comments or macros. SWIG is certainly worth a look, and there are other tools.
The fundamental point of my answer is to try to get across the idea that such translations are not as automatic as you might hope. Personally, I always end up writing my p/invoke declarations by hand. This allows me to get them exactly the way I want, and maintenance is not really a big deal because DLL interfaces typically don't change. They don't change because you don't want to break binary compatibility.

Call C# dll from unmanaged C++ app without COM

Is there a way to call c# dll from c++ unmanaged application without COM usage?

You can do this using Reverse P/Invoke - example and discussion here.

It is actually possible to disassemble, modify the IL, and reassemble it with exported functions. I messed with this a few years ago, and created an application that would disassemble a dll, provide a list of functions that could potentially be exported - allowing the user to select them, then re-write the IL and reassemble everything. Then, I could call directly into the dll from unmanaged code...or p-invoke into the dll from managed code (not really practical, but interesting nonetheless).
Surely there is a reason that this isn't supported in the .net languages themselves (even tho it is supported in MSIL). I wouldn't use this in production:
Dead link:
http://www.csharphelp.com/2007/03/exporting-managed-code-as-unmanaged/
Wayback Machine:
https://web.archive.org/web/20140213030149/http://www.csharphelp.com/2007/03/exporting-managed-code-as-unmanaged/

I might be a bit late, but check this out.
Using this little msbuild task, you can create a C# library that can be called as if it were a native DLL. (e.g. write plugins for apps that require them to be native dlls)
Oh and don't forget to use the project template, which will setup everything for you.

Your only option really is to either use C++.net or create a C++.net wrapper for it that exports what you need.
Calling C# code from C++

what are the possible ways to using c# code in c++

I'm just looking for a best way to re-use code written in c#, in my c++ projects. Creating a com\service doesn't look like a best option for my needs. How difficult it is to export c# code into a dll and use it in c++? can i get some suggestion or example? is this usual requirement or ? Please help me.
i use win7, VS2008, win7sdk
Thanks & Rgds, ~calvin

Executing managed code from an unnamaged executable is possible, though not quite easy. You can look into this article for an introduction and this book to go further.
I personally would avoid this kind of things in most cases and, if possible, switch the C++ project to C++/CLI to obtain an immediate compatibility with .Net assemblies for a minimal cost.

You can't export C# code into a native dll afaik. At least without very much pain in your buttocks. You should have thought beforehand and write the reusable part in C, thus creating a native DLL which could be used from all languages.
Also, you could try managed C++ - I personally hate it... but there you go

In case you need to use code written in C# C++, then you need to first see what all data types you would be passing from your C++ code to C# code.
1. Basic data types like int, enum etc can be passed from unmanaged to managed code.
2. in case you want to pass on class object, than you need to use marshalling.

If you can't use COM (if the .NET code is already written for example), then you can host the CLR, but this is a long road...
See these other articles
How to load CLR into process and Create a C# DLL That Can Be Imported in a Delphi App Using stdcall - Possible?

Easiest way to generate P/Invoke code?

I am an experienced .Net programer, but have not compiled a C/C++ program in my life. Now I have this C-dll, headers and documentation (3rd party, not from Win API), from which I need to call about ten methods.
I was thinking of using Platform Invoke. I found these three tools that would create the code for me:
PInvoker: http://www.pinvoker.com
P/Invoke Interop Assistant: http://www.codeplex.com/clrinterop
P/Invoke Wizard: http://www.paulyao.com/res/pinvoke/pinvoke.aspx
and possibly
Swig: http://www.swig.org/
Pinvoker seems to have a bit different approach than the Interop assistant and the Wizard. Swig I just found when checking that this question has not been asked here.
What are the pros and cons of these tools?
What would be the best = easiest and safest way for me to produce the P/Invoke code given that I don't know much about C/C++?

See http://dotnetperls.com/dllimport-interop for an interop example, and this MSDN article for more info. The bible for this stuff is Adam Nathan's book.
Basically you will need to identify the functions in the DLL you want to call. These need to marked with extern to make them accessible to the outside world. The next step, which can get tricky is writing a DllImport for the function. This needs to map between the managed and unmanaged worlds. You will need to work out how to marshal any complex data structures from the C dll into managed code.
You should check to see if there is any sort of COM interface to the DLL. Make sure you really need to use P/Invoke first.
SWIG was originally for wrapping C/C++ code for use from scripting languages. It generates C# code from an interface description (see tutorial). I wouldn't recommend using it from C# if P/Invoke is an option.

if the signatures of the functions are simple then it should take 10 minutes to setup - ie if they take 2 char * and return an int. Its only once they get complicated that it gets messy
The bible on pinvoke is Adam Nathans - .NET and COM: The Complete Interoperability Guide
And I agree with other poster - swig is not the right thing

Need to 'wrap up' a C++ dll/h/lib/xml/exe based SDK into a COM to use in a C# 2.0 project

I just got handed an SDK made of C++ dll, lib, exe, and various .h files. I presume it is meant for C++ developers. The sample projects they provide with their documentation are all written in C++. I am able to spin them up with Visual Studio 8 (2005) and run them. They do control the device as advertised. However the project this needs to be used by is in C# .Net 2.0 and that is unchangeable.
My boss was a C++ developer and says all I need to do is to compile it as a COM object and then import the COM object into my C# solution. My boss says it should take less than an hour to "wrap" there SDK up as a COM object, even for me with no knowledge of C++ compiling.
I've used COM objects in C# solutions before so once this is made, I can continue on from there without a problem.
However, I don't know what to do to make the COM object from the 2 .dll files, 1 .exe, 1 .lib file, 1 .xml file, and the 12 .h files. Is there a resource available to tell me what to do to make this happen?

My boss was a C++ developer and says all I need to do is to compile it as a COM object and then import the COM object into my C# solution.
That's true, however compiling it as a COM object is "difficult" (by which, I mean that you can't do it) unless it already implements the COM APIs (if it doesn't then you need to implement the COM APIs before you can build it as a COM object).
There are books (for example, Essential COM) which explain how to to create COM objects using C++, but it's non-trivial (for building COM objects there may be better books than Essential COM, and better/easier tools than C++).
I think you and/or your boss have 3 options:
Ask the vendor to give them to you as COM objects
Design a COM API that would wrap the SDK's API. Create a COM project (in the language of your choice) which exports this API. Implement these APIs by invoking the underlying SDK methods. To do this you may need someone who knows C++, or be willing to spend much, much longer than "an hour" on this project.
Forget about using COM; instead, build the SDK as a DLL, and use PInvoke to invoke it from .NET code.
My boss says it should take less than an hour to "wrap" there SDK up as a COM object, even for me with no knowledge of C++ compiling.
Based on what you've said I don't know of any way to make that happen.

Tell your boss if it would take him less than an hour to wrap it up, he should certainly do it: it would be a more efficient use of both your time.
I would also suggest ATL (not using attributes), but this is something which can take some time to get right if you're not experienced.

My boss says it should take less than
an hour to "wrap" there SDK up as a
COM object, even for me with no
knowledge of C++ compiling.
That may be true for an experienced C++/COM developer, but not for a beginner. I think your best bet is to use ATL. Take a look at the MSDN tutorial.
And do not use attributes.

This doesn't quite answer your question, but...
One option instead of trying to make a COM object is to use P/Invoke and just call the methods in the DLL.
This thread on the MSDN Forums documents how to make a DLL to call using P/Invoke.
Of course if you need access to a whole class (and make an instance of said object), this isn't going to be helpful.

It's good that the code compiles and runs for you. That said it's totally unfair to assume you can do this in an hour.
Have you checked to see what is actually being built by Visual Studio. There could be a chance that it is already building a COM object.
Investigate how the code is being called. I assume you have a .exe that you can run to test the code. Step through this in the VC++ debugger (it's similar enough to debugging C# code) and try to identify any API calls that match with your docs/expectations. This knowledge will be helpful if you try to go the P/Invoke route.
Something else to consider is SWIG. This is typically used by Python developers to wrap C/C++ code and provides some support for C#.
The managed C++ route is probably more advisable for experienced C++ devs because you need to understand a lot about memory allocation, for all but the simplest code.

I (well, really my lead and I) will first try using p/Invoke (via the DllImport feature of System.Runtime.InteropServices) against the SDK's dll the company provided. I'll let you know how it goes.

I think what you really want/need is C++/CLI, that way you can just build them directly into a managed assembly. The idea is that you write a pretty plain wrapper that looks like kind of a cross between C# and C++ and then it does the rest.