I was wondering if I can use a library -written in C++- in C#
The problem is that library has its own structures and classes..
Will I be able to use it in C#?
Thanks
EDIT This library is open source..
so if my requirements needs something special in C++ code, I will be able do it...
You cannot directly use C++ classes in managed code. The chief problems are not being able to use the same memory allocator as used by the C++ code and not being able to invoke the constructor and destructor easily. A Microsoft employee posted a blog post to show that it is not impossible. I would not recommend doing this.
COM is a solution but that invariably requires a fairly big rewrite and good COM programming skillz. A managed class wrapper in the C++/CLI language is usually the best solution. You could take a peek at the SWIG tool to consider auto-generating those wrapper classes. Beware however that this tool can easily create more problems than it solves.
There are two ways, both using an Adapter (which maps C++ classes to .NET classes):
C++/CLI
COM
The former avoids going via COM, and much of the C++ code might be able to be just compiled with the correct switches.
Additional: In theory P/Invoke might be possible, but all the C++ semantics would be lost, you would need to handle C++ object lifetime manually (and instance references as IntPtr). Plus of course you would need to call the mangled names...
Another option is to write a managed wrapper in C++/CLI. I prefer that instead of using P/Invoke.
Related
If this has been asked, please accept my apologies. I can't seem to find much on the subject. Primitive types pass template parameter between c++ and CLI is a similar question, bit I didn't find it very informative.
I have a native C++ DLL that exposes a template class (an instantiation of it, of course), and I wanted an analogue of it in C#. I'm relatively new to C#, but I know the closest thing is a generic.
My problem is how to wrap the C++ template in a C++/CLI template/generic so as to be able to use it in C#.
Is it even possible? I'm thinking this is impossible, because the CLI wrapper wouldn't know how to marshall the unmanaged, unknown type T into a managed type for C# consumption.
If it is possible, how do you go about it? If not, what are some general strategies you could use in similar situations?
Thanks.
Assuming you're talking about unmanaged C++ then it's not really possible.
In general, passing anything complicated from unmanaged C++ to C# is a right pain.
The easiest thing to do is to write a simple struct in C++ that you can use to pass data between managed and unmanaged code. (In other words, a Data Transfer Object.)
Then write an unmanaged function (that uses a C signature rather than a name-mangled C++ signature) which wraps the C++ methods, and call that wrapper function from C# instead.
I've done this a few times, and it's very much more manageable than trying to call unmanaged C++ functions from C#!
You stated that the template class is exported from the DLL already, which means it is an instantiated template class.
An instantiated C++ class has no difference than regular C++ class from the point of view of P/Invoke. Calling instantiated template class is possible and doable from C# directly without using C++/CLI although manually writing the wrapper code will be very time-consuming.
I have shared the way of doing this manually on stackoverflow at C# pinvoke marshalling structure containg vector<structure>, but it will take you too much time to manually write a wrapper class this way, it may not be worth the effort.
The tool I wrote, xInterop NGen++ can generate the C# wrapper class for the template class. It can generate wrapper classes for any C++ classes exported from a native C++ DLL as long as the same DLL can be used from traditional C++ application.
You may want read the details at the links below on my blog web site.
Advanced technology to wrap native C++ template class in C# automatically
Creating and Accessing Instantiated std::vector Template Class from .NET
I do have a plan to release an express version for free in the near future if the budget is your concern. So, if you have a small project with the need of calling a few C++ template class, you might be able to use the free version with limited features to create C# wrapper class. I also have plan to release generated C# wrapper(C# binding) for a couple of open source C++ projects.
(I am the author of xInterop NGen++)
It's doable if you are willing to provide an explicit list of supported template argument types and managed<->unmanaged conversion functions for these types in the C++/CLI wrapper. See the code here.
I need to create a VC++ wrapper in C#. Is there a way to automatically generate the code?
Edit: let me clarify a bit: I have a simple project with complicated math functions (computing magnetic declination) in c++. Its just three files, one header, one command line controller and the library.
I was looking at SWiG but I found it to be enigmatic :P. I'm taking a look at C++/CLI.
Any tips and pitfalls to watch for?
Take a look at: Using Unmanaged C++ Libraries (DLLs) in .NET Applications
Or you can use C++/CLI
SWiG supports C#. But a C++/CLI wrapper will be much more ".NET-like" than one automatically generated by SWiG.
You can have a look at this tutorial:
http://www.codeguru.com/csharp/csharp/cs_data/article.php/c4217
I think it's better if you make your own wrapper than using any tool (if it does exists). The reason is that you can create a better C# wrapper using the right philosophies instead of generating a list of function call from a DLL.
And for the pitfalls, the only thing I can say is that since you are going to mix manage and unmanaged class, be sure that your struct/parameters are matching (sizeof or types).
As for most short questions: It depends on your settings and requirements! ;-) If you have a more C style interface, you might be able to solve your problem just by using Interop. If "real" OO progamming and C++ are involved, you probably have to look at C++/CLI. That can be easy, but it can also become painful - depending on your classes. As far as I know, there's not automatic code generation tool.
this might be a simple question, but as I have zero experience in C++ and my boss has given me a C++ solution work with I need to ask this question.
I have a C++ solution that needs to be turned into a .NET class library which can then be used in another .NET solution done in C#.
Is this even possible???
Cheers
You have to wrap all C++ classes that should be visible in .NET in C++/CLI classes.
Read this
There are also some automated tools to do this, but I never used these (I don't really trust them). Depends on how many C++ classes do you have, and how complex they are. Writing the wrappers is mostly straight-forward once you get used to some oddities of C++/CLI.
It depends of the output of the C++ solution. Is it an application (*.exe) or a library (*.dll)?
If it is a library (*.dll) you can use Platform Invoke Tutorial to call its functions out of managed code. A lot of examples of calling Win32 native functions can be found at http://pinvoke.net/.
If your result is an application it could be possible, that it has a COM interface. In that case you could use the COM interop to communicate with your application.
Last but not least you could write with C++/CLI a managed wrapper around your C++ functionality. But this is a lot of work and has many pitfalls.
Thus far I've figured out out I needed to recompile the library as a .dll instead of a .lib, enable /clr and /EHa instead of /EHsc. Now I've got a managed dll which I've added as a reference in my C# project.
Now how do I use it?
I'm prepared to write some wrappers, but I don't know where to begin or how to "see" what functions I've gained access to. I've read a little bit about how the class names and functions might be mangled by the compiler... do I need to go back and add __declspec exports everywhere (if so, how?), or is there an option in VS2010 that says "don't mangle it!"?
The C++ library in question is still under active development, so I'm hoping I can modify the C++ library as little as possible and just recompile it periodically with a few switches, and then expose the new functionality as I need it.
If you are going to compile your C++ (if originally was unmanaged C++) you will need to do much more than just add the /clr switch. In order for C# to use the DLL you will need to create managed classes and other types based on CTS which are compatible with C# (.NET).
See and ref classes.
A good book to read about the subject (IMHO) is this one
You can either expose the functions as C style functions (i.e., no mangling) from your dll or you can expose them as COM objects.
I'd suggest writing a COM wrapper, and using that instead. Have a look at http://msdn.microsoft.com/en-us/library/035x3kbh%28v=VS.80%29.aspx for intro instructions. You'll want to make your object interfaces derived from IDispatch and be automation compatible, which should enable the runtime to consume them without any custom marshaling.
A nice benefit of this approach is you can continue to build your native code as a library, and just make your COM project use it. Also, it's still native code inside the COM object, so there's much less potential for unknown problems (once you get the interface layer working).
That's my suggestion, anyway.
Yes, wrap it in à COM object. I believe ATL is what you meed to do this with the least effort.
Is it possible to share references to C# objects between C# and C++ code without massive complexity? Or is this generally considered a bad idea?
The best solution for sharing a C# object between native and managed code is to use COM interop. This allows you to essentially share an interface of an object between managed code and it's equivalent signature in C++.
As for the complexity side of things. The majority of COM interop scenarios are straight forward and really are no more complex than good old COM programming. On the managed side it looks really no different than a normal interface.
Once you introduce multiple threads or start playing around between COM apartments though, things can get a bit tricky.
In my experience, the easiest way to get this working is the following.
Define an interface in C# that you wish to use in C++
Mark the interface with the ComVisible(true) attrbute
Run tlbexp on the assembly which generates a TLB file
Import the TLB into your native project
This will get the interface definition into both of your projects. How to pass that between the projects requires a bit more detail into your architecture.
Another solution I can recommend, from personal experience, is to use a managed C++ interface between the two if the C++ code you want to access is too large or too complex.
For example, I am using the RakNet C++ network library in a C# project. The solutions are to either create a massive wrapper class in C# to access the required C++ functions, create a C++ wrapper around those functions which can than be used as a COM interop or use Managed C++ (Visual C++/CLI).
I chose the latter which allows me to use C++ to access the RakNet library, but the classes created can be used directly in another .NET project as if. So the main logic has been created in those Managed C++ classes, which also allow me to use the .NET framework and some of its wonderful features. In my C# project I simply need to call the Managed C++ library which provides me with all in all 20 functions I need to perform everything.