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.
Related
I'm a regular .NET developer aiming to integrate a C++ library into a .NET project. I have a few ideas, but since I'm new to C++ in general I don't know the limits of the technology I'm trying to work with. The C++ project is essentially a fast sound renderer that can playback multi-track audio files with a bunch of different postprocessing tricks. All of this is cool, but considering I have a simple .NET WinForms app I want to integrate with, things start to look messy.
Firstly, the C++ project has no .NET bindings or ActiveX/COM integration. Its a plain 'ol MS VC++ 9 project. If I am to work with the project in my .NET app I'll have to somehow interface with it, ie. create class instances, set properties, call methods, marshal data in and out, etc.
Secondly, its built to run as an independent Windows app and manages its own windows using the MS Windows API. This is fine, but somehow I need the .NET VM running in the background, managing the show and running all my C# code. I don't write C++ so I need to stick with C# to build an app around this lib.
Thirdly, whether I'm running in the same process as the C++ lib or not, I need a way to build/interface/debug these 2 separate apps as if they were one. I have no background in C++ programming except for the fact that I have written a couple C++ DLLs for high-performance data manipulation.
So, many questions and no idea how to start!
I can fully compile this lib and get it into a VC EXE, but how do I co-compile my .NET code into it? Or alternatively, how do I compile the C++ code into the .NET EXE so it runs within a managed environment? Note that it wasn't designed for this and may misbehave if I attempt to change too much.
The main problem is interfacing with it. How do I expose some C++ classes to be accessed from .NET? I know exactly which classes I need and I'll need only a couple dozen classes along with their relevant methods/properties to be available from .NET. I don't mind handwriting wrapper classes in .NET to help the .NET VM understand the class structure of the bytes transferred back and forth. I'm hoping I can directly work with C++ objects from a managed environment so most of my code can remain in .NET.
Even if I run it as an independant app, would I have to resort to sockets or something to communicate with it? This is the absolute worse case and I'll do anything to avoid this.
Any help or pointers are appreciated, I hope I made myself and my task at hand clear and that my questions are specific enough and answerable. Thanks for any help!
Edit: If I write wrapper classes or generate them, can I use P/Invoke to create class instances and call methods on them and have them run native C++ code in the background? Where will the memory for such C++ objects be stored and managed? Within the .NET heap or outside it?
You can write managed C++ (C++/CLI) wrapper to unmanaged C++ code. It would be the most flexible solution. Basically, you write a .NET assembly in C++, the assembly exposes managed classes which call your unmanaged code. Then you can reference this assembly from your C# projects.
There is a very basic article how to do that: http://www.windowsdevcenter.com/pub/a/dotnet/2004/03/29/mcpp_part3.html
This might be helpful as well:
http://www.multicoreconsulting.co.uk/blog/c-snippets/how-to-call-unmanaged-cplusplus-from-csharp/
And MSDN article .NET Programming in Visual C++.
Option 1
If you intend to use unmanaged C++ objects, it is probably better to write a managed wrapper in C++/CLI that has the same interface as the class that it's wrapping, but has a managed constructor and destructor to clean up the unmanaged resources. In C++/CLI you create unmanaged objects just like C++ that you have to delete yourself, or you can create managed objects with the gcnew keyword. The .NET facing side of the wrapper would take managed objects. The Native facing side of the wrapper could operate on all of the unmanaged data types that you already have.
For example, consider the unmanaged class Frobber. In C++/CLI, you would create a class called ManagedFrobber that would have all of the same methods as Frobber and contains a private instance of a Frobber. In the ManagedFrobber constructor, you would create your private Frobber instance. In the ManagedFrobber destructor, you would delete your private Frobber instance. Every method in your managed wrapper class would simply call methods on the private Frobber instance.
Option 2
If all you intend to call from the C++ world are c-style functions (static in the C# sense I guess), then P/Invoke is probably the way to go because then you don't have to worry about all of the nuances of a wrapper class. For example, if you pass an array from the Managed world into the Unmanaged world using a wrapper class, you have to worry about things like pinning the array in place so it doesn't get moved around by the .NET runtime while the managed world is messing around with it. With P/Invoke most of these nuances are handled for you.
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.
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.
I'm using a small C webserver. I'm doing some of the actual request processing with C# libraries.
I'm using a glue layer which appears to be written in something close to c++ to join the two worlds. It provides a 'public ref class' which I can derive from in the C# world.
If I want to derive several different classes from this in C#, how do I create instances of these derived classes from the C/C++?
What information (the class name? A factory function?) shoud I pass (and and in what form) from the C# to the C/C++ code?
I would like a solution compatible with .NET 2.0, and I'm using Visual Studio 2008 to create my code.
I have realized several times that people are sometimes not completely aware of the difference between managed and unmanaged code, so I would just like to summarize:
You cannot simply call managed code from a native C++ application. In order to call it, you will first have to expose your .Net code to COM, and then instantiate a COM object in C++. This way your native app thinks it is creating a COM object like any other, and .Net is doing all the interop in runtime.
Second way is to use managed C++/CLI (which is not native C++, but supports both worlds). This way both C++ and C# apps are managed and can communicate seamlessly. So as long as the "glue layer" is written using managed C++/CLI, you can both work with native and managed data.
As your originally mentioned unmanaged C++, then the answer would be to go for 1st solution: expose the managed object to the native world through COM interop. If you don't mind using managed C++/CLI, then you have a simpler solution - you can instantiate managed classes easily (with some changes in syntax you should quickly get used to).
See How to call a managed DLL from native Visual C++ code in Visual Studio.NET or in Visual Studio 2005.
http://support.microsoft.com/kb/828736
Use the #using directive to import your C# assembly into the C++ code.
#using "ThingLib.dll"
using namespace ThingLib;
If you only want the C++ code to be aware of the base class, you'll need to call some kind of factory method.
ThingBase^ thing = myThingFactory.MakeThing(aParameter);
If you want to actually instantiate the derived classes in C++, use the gcnew operator.
ThingBase^ thing = gcnew DerivedThing(aParameter);
There's a good summary here of the new C++ language features for talking to managed code:
http://msdn.microsoft.com/en-us/library/xey702bw.aspx
Is it possible to use a C++ .lib file from within a C# program?
There are plenty of ways. Read about "interop" in MSDN..
One way is to expose the lib as a DLL, and then use pinvoke to call these functions from a C# project. That limits you to a C-style interface, though.
If your interface is more complex (e.g. object oriented) you can create a C++/CLI layer that will expose the lib's class structure to your C# program. This means you'll have to create a managed C++ (or C++/CLI as it's now called) project; then design an interface in managed code that will be implemented by calls to native C++ (i.e. your lib).
Another way of doing this is by wrapping your lib with a COM interface. But COM's a pain, so I wouldn't...
Not directly. You can create a C++/CLI assembly that consumes the lib and then access that from C#, or you can wrap the lib as a DLL.
What you need is a managed wrapper (C++/CLI) around the native C/C++ library that you are working with.
If you are looking for any C++/CLI book I'd recommend Nishant Sivakumar's C++/CLI in Action
Already answered to wrap it but here's an example . Good luck!
I would take a look at swig, we use this to good effect on our project to expose our C++ API to other language platforms.
It's a well maintained project that effectively builds a thin wrapper around your C++ library that can allow languages such as C# to communicate directly with your native code - saving you the trouble of having to implement (and debug) glue code.
No. You can only use a full .dll from a C# program.
That depends, do you have any limitations on this scenario?
If you have a lib file, it should be possible to first compile it into a DLL file, secondly exposing the functions you want to call in the DLL interface, and thirdly, call them using C# native methods (have a look at pinvoke.net on how to do this bit).
you can't use a lib, but like the others said, you can use it if you wrap it into a dll.
swig can take the headers of your .lib, and if they are not too complex it can generate the dll for you which you would then call with a pinvoke from c# which would also be generated by swig.
if your library is complex and has reference counted smart pointers everywhere, you should find an alternative.