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.
Related
Is it even possible to create GUI layer in C# and rest of application in C++? If I am not wrong one of antyvirus software had GUI made in Delphi. How it could be done ?
You have several options for doing it, including:
Use P/Invoke to call into the C++ DLL from C#.
Expose a COM interface from the native code, and call it from C# using COM interop.
Write a native Windows service and call into it from managed code.
Use C++/CLI to write a managed library in C++, which you can easily link to from C#.
If you're starting from scratch, option 4 is probably your best option. (Aside from just writing the whole thing in C#, that is.) The first three options all involve some additional wrangling and overhead, and probably aren't worth the hassle if you don't have a compelling reason such as needing to interact with an existing native library or having some need for a service-oriented architecture.
If you write your business logic in C++/CLI, and your UI in C#, it shouldn't be a problem. If you want to write in pure ANSI C++, you might have to write C++/CLI wrappers around the objects you want to expose to C#.
write the app logic in c++ dll, then use pinvoke from c# to talk to the dll.
See this answer. It seems to answer your problem
My question is what's the best way to create an inteface with C++ code.
Basically so far I have a console project in c++, that works as I expect to, but I now want to make a GUI for it. The choices to me seemed to be:
Make a dll of the c++ project, and then make a C# form which uses the dll to do the logic.
Same as 1 except with VB.
Use QT or something eqvilent and make the inteface in the same project.
I've been trying option 1 for quite sometime. I made the library I believe successfully by making a library project in Visual Studio 2005. I then put it in my c# project but I then had a problem of being able to instantuate my class, but the c# project couldn't see my methods.
The only fix I could find to this was to use the ref keyword. The problem with this was then not being able to mix managed and unmanaged code and trying this on one of the larger classes produced about 250 errors.
Option 2 i had the same problem with.
I'll start option 3 if I have to, I just wondered if I was missing anything fundamental or any suggestions in general?
Cheers for reading.
You absolutely can use C++ code from C#, but if it's unmanaged C++ code, you have to delve into the realm of pinvoke to call your code.
If you're attempting to leverage an existing C++ library from .NET, one of the easiest ways to do this is by using C++/CLI as a wrapper around your unmanaged library. C++/CLI compiles into .NET bytecode, but features lots of automatic unmanaged interop. A phrase that's often floated about when using C++/CLI unmanaged interop is "it just works". It's an accurate phrase.
Once you have a C++/CLI wrapper for your unmanaged code, C# should be able to see everything exposed by your C++/CLI library.
We have a moderate size (40-odd function) C API that needs to be called from a C# project. The functions logically break up to form a few classes that will comprise the API presented to the rest of the project.
Are there any objective reasons to prefer P/Invoke or C++/CLI for the interoperability underneath that API, in terms of robustness, maintainability, deployment, ...?
The issues I could think of that might be, but aren't problematic are:
C++/CLI will require a separate assembly; the P/Invoke classes can be in the main assembly. (We've already got multiple assemblies, and there'll be the C DLLs anyway, so not a major issue.)
Performance doesn't seem to differ noticeably between the two methods.
Issues that I'm not sure about are:
My feeling is C++/CLI will be easier to debug if there's an interop problem; is this true?
Language familiarity - enough people know C# and C++, but knowledge of details of C++/CLI are rarer here.
Anything else?
In the case where I am working with an existing C library, I prefer PInvoke. PInvoke, while a bit tedious and troublesome at times, is a fairly well understood technology that has an ever growing set of tools and internet documentation available. Generally speaking, whatever problem you run into, there is already a sample available on the web, or a quick check on stack overflow will provide a solution.
C++/CLI is a great technology, but IMHO its documentation is limited as compared to PInvoke for interop specific scenarios. It also doesn't have the tooling infrastructure for interop solutions that PInvoke has. Adding a C++/CLI assembly for a scenario that can be solved with PInvoke just seems too costly to me.
On the other hand, if I'm working with a large C++ library, I consider C++/CLI a bit more. PInvoke does not work with C++, and I must end up adding some kind of intermediate layer. Either a small C layer to wrap all of the C++ function calls or a C++/CLI library to bridge the gap. C++/CLI feels a bit more natural to me in this case.
It depends in large part how memory ownership is handled. P/invoke can marshal pointers only when memory management is one of a couple particular ways, usually caller-allocated buffers. If your API returns pointers (via return value or out parameter, doesn't matter) and expects them to be handed back to a destruction function later... p/invoke will either do the automatic marshaling or give you direct access to the pointer value you need to send back later, never both. So C++/CLI becomes a very desirable approach in that case.
Think of P/Invoke as platform invocation, are you calling into something like the Win32 API which is very P/Invoke friendly or do you need to provide .NET bindings for an unmanaged library?
Since the wrapper typically is very thin a C++/CLI wrapper doesn't necessitate that you know C++/CLI specifically. What you need to know can be found in the language specification, it's an extensive documentation with lots of examples. P/Invoke is more of an nice to have feature for smaller well established existing libraries, but if the interface for calling into that library changes you'll run into a problem. With C++/CLI you can still have a public managed interface in your C++/CLI project that's exposed for managed code and handle changes to the C API more easily that way.
If you wanna get rid of the extra DLL you can always try ILMerge, but I'm not sure if it's capable of handling mixed assemblies, (apparently not), but it looks like it's possible to link both managed and unmanaged *.obj files with the PlatformSDK linker like this:
cl.exe /MD /c /clr Unmanaged.cpp
csc.exe /target:module /addmodule:*.obj Managed.cs
link.exe /DLL /LTCG /NOENTRY /CLRIMAGETYPE:IJW *.obj Managed.netmodule
C++/CLI will be easier to debug if you have personnel who know how to debug C++. If you don't, it could potentially be much harder.
I would suggest that the tradeoff here is between ease of use for the consumers of your interop assembly versus ease of maintainability for the assembly itself. If you have a solid core of senior engineers who are familiar with C++ and who can reliably maintain the assembly, it will be much easier on the rest of your team who are unfamiliar with native code to give them a fully managed interface that takes care of everything for them.
On the other hand, if you're the only person in the shop with C++ experience, I would be very leery of embedding a C++ module into the project, in case someone else has to maintain it later.
For an API of this size (~40 total entry points), I would draw the dividing line between C++/CLI and P/Invoke based on how much "header file gunk" you must duplicate in C#. If it's a small (to modest) amount, P/Invoke is fine. Once you start duplicating a lot of .H files in C#—especially for things that aren't exposed in your .NET API—you might be better off using C++/CLI.
Lots of good answers here - another perspective is the plan for the existing C API.
Arguments for using PInvoke include:
You need to keep a C API around for
compatibility with other C consumers
You need to keep the code in C as
it's large and migration is too
expensive
Arguments for using C++/CLI include:
you want to move as much of the code as possible to the CLR
In this case you can start with C++/CLI and then move more and more over to C#
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.