Keeping C# and C++ classes in sync at runtime? - c#

My application is built in two sections. A C# executable which is the front end UI and a C++ dll which is more the low-level stuff. My application creates and manages many instances of objects, where every C++ object instance has a corresponding C# object instance. What techniques or libraries can I use to ensure that objects in the C# and C++ sections and data in those objects are always in sync at runtime? A change of one member in one object instance should update the corresponding object instance.
Thanks!
Edit: clarified a little what I meant by keeping the objects in "sync"

Perhaps code-generation would work well. E.g. define the properties/methods for these classes in one spot (maybe XML or something) and generate C# and C++ classes from that. Perhaps use something like CodeSmith (http://www.codesmithtools.com/) to generate your code.

It's not quite clear whether it would solve the problem, but have you considered Managed C++? I have had pretty good success simply compiling my C++ code as Managed C++, then using the managed extensions to create .NET classes that use the underlying C++ data directly. That way, there's only one copy of the data.
Probably not suitable for every situation (and I haven't tested its limits by any means) but I found it quite a timesaver. And since Managed C++ is a proper .NET language, the result was clean to use from the C# side, with none of the usual oddities or quirks one often has to work around when trying this sort of thing.
(Another similar approach would be to use SWIG (http://www.swig.org/) to generate wrappers for you. I hear it is easy to use and works well, but I haven't used it myself.)

Related

Use C# properties in unmanaged C++ code

We have a large project mainly written in C# (services, multithreading etc.). However, the core number crunching algorithms are written in unmanaged C++ to be fast (OpenMP etc.).
Unfortunately, at the moment we have to do a lot of effort to exchange data between these two worlds. I.e., we have to write wrapping classes in C++/CLI for each of the C++ classes. For (virtually) any required setting (Properties) in the C#-"world" there is a copy in the C++ world (a header file) and an explicit conversion back and forth in the wrapper class. This architecture seems very inefficient and quite error-prone.
Primary question:
Is there a way to share a C#-class with properties somehow automatically in unmanaged C++? (we have to read and write!)
Secondary question:
Could you give any advice of how to improve the architecture in a case as described above. One consideration of ours was to completely switch to C++, but having to find appropriate libraries and write clean code for all the (system-)things we do in .NET at the moment does not feel good.
Many thanks for your help and best regards,
Jakob
I am dealing with similar issues at my work where my primary task is to write managed interfaces to certain high perfromance, low latency dlls, this involves simple cases where I have to wrap the native classes using simple c++/cli containing a raw pointer to the native class or more complex issues where the native code is a server side publisher and the managed code has to subscribe to it using delegates ie they have to be converted to native callbacks.
.NET under the hood is a sophisticated COM server as far as I know. It is possible to write .net assemblies with the ComVisible attribute set to true then it acts as a classic COM component and then it is possible to use it from the native C++ code as a COM component. The reverse that is to use native code from managed can be achieved using the DllImport attributes and all the Marshaling can be fine tuned by the various attributes like the StructLayoutAttribute (http://msdn.microsoft.com/en-us/library/system.runtime.interopservices.structlayoutattribute.aspx) and the MarshalAsAttribute (http://msdn.microsoft.com/en-us/library/system.runtime.interopservices.marshalasattribute.aspx)
I am also using sometimes the unsafe keyword as well. I have to deal with high performance code so in some cases it is that after profiling that I know which is the best solution. Whether it is the warpper class solution that you have mentioned or the classic COM way, or some kind of hybrid with some caching, object pooling etc.
Hope that helps. :)
Apologies if that looks a bit disorganised. It is very late here. :)

How to smoothly develop a C lib for C#/.NET?

I am developing a complex library in C++ and i plan on having a C interface so others can load up the DLL and easily access the lib. I haven't tried writing code in C# that access C code. I did a quick google and found code that uses a lot of attributes.
What can I do to keep my interface simple enough to not cause a headache trying to keep .NET in sync with it? Is there some kind of header generation tool i may use? Do i only use simple POD structs? I'm unsure how i should handle types as they are passed around as pointers. I am also thinking maybe i should avoid using anything that is a not an int/string or array.
I am developing it using MSVC but mostly using it with GCC. I know i should use the calling convention __stdcall. Beyond what i said i am totally clueless. I actually dont know how to load the DLL into .NET.
What can i do to ensure everything works correctly when writing my C lib and getting it to run with .NET?
Consider putting together a COM interface. Consuming COM from .NET is marginally easier than P/Invoke; at least you won't have to spell out prototypes for all functions in C#, the COM typelib importer will do that for you.

Calling UNIX and Linux shared object file .so from c#

Is there a way for a Shared Object file written in C and built on Unix to be called from C# P/Invoke?
Or do I need to use Java or something like that?
Mono has the ability to integrate with native libraries from within C# built on top of dlopen(3). You just have to use the DllImport statement with the name of the library (i.e. 'libform.so.5'), then wrap the native code and data types with a friendly C# class that takes care of all the low-level stuff. This page has a good overview with lots of information on how to deal with marshaling pointers and other unsafe types.
Once you've got your wrapper class written, you can just use that without worrying about the fact that it's using a native shared library underneath.
I would say at the least there's likely to be no easy way, especially if you mean C# on Windows. In that case you would need something that would be able to decode the shared object and get to the code in it, sort of a re-implementation of the ABI for GNU/linux. Also, any other libraries would have to be present and usable as well, such as the C runtime library and the like. This would likely be a very significant effort.
As for doing it directly under linux/Mono, see this answer: Calling UNIX and Linux shared object file .so from c# .
You could also try to see if what open office does, http://packages.debian.org/lenny/cli-uno-bridge could be helpful; but this is more of an interface rather than directly linking the two together.

Marshal a C++ class to C#

I need to access code in a native C++ DLL in some C# code but am having issues figuring out the marshaling. I've done this before with code that was straight C, but seem to have found that it's not directly possible with C++ classes. Made even more complicated by the fact that many of the classes contain virtual or inline functions. I even tried passing the headers through the PInvoke Interop Assistant, but it would choke on just about everything and not really no what to do... I'm guessing because it's not really supported.
So how, if at all possible, can you use a native C++ class DLL from .NET code.
If I have to use some intermediary (CLR C++?) that's fine.
There is really no easy way to do this in C# - I'd recommend making a simple wrapper layer in C++/CLI that exposes the C++ classes as .NET classes.
It is possible to use P/Invoke and lots of cleverness to call C++ virtual methods, but I wouldn't go this route unless you really had no other choice.
You might have a look at SWIG, if nothing else just to see how they handle the basic wrapper code (which SWIG generates). I know next to nothing about C# native code bindings so I can't judge if their approach is sound, but they do a decent job with some of the other language bindings.

What are the situations or pros and cons to use of C++/CLI over C#

I have been keeping up with .NET CLR for awhile now, and my language of choice is C#.
Up until recently, I was unaware that C++/CLI could produce "mixed mode" executables capable of running native and managed code.
Now knowing this, another developer friend of mine were discussing this attribute and trying to determine when and how this ability would be useful.
I take it as a given that native code has the capability to be more efficient and powerful than managed code, at the expense of additional development time.
In the past, I resorted to strictly native C++ code libraries and used Interop to make use of the functionality I wrote into the native library.
I can see the benefit of not requiring an additional library, but I'm curious as to what all the pros/cons of using C++/CLI over soley managed executable created in C#, or such an executable using Interop to call a purely native C++ library?
(Sidenote: Are the terms Interop/PInvoke interchangeable, as I d.on't understand the difference between the terms, simply seen them used the same way.)
With C++/CLI you can create, broadly speaking, three types of objects:
Managed types. These will compile down to essentially the same IL as the equivalent C#. There is no performance opportunity here.
Native types. Compiles down to native code as if you'd used straight C++.
Mixed mode types. These compile down to managed code, but allow you to refer to native types too.
You might think of (3) as being like writing C# code with PInvoke code to accessing the native stuff - except all the PInvoke stuff is generated for you.
There's more to it than that, of course, as well as some caveats - but that should give you an idea of how it's useful.
In other words it's really a glue language. While you can write fully fledged apps in C++/CLI it's more normal to keep the managed and native parts separate and use C++/CLI to bridge the two more cleanly than with PInvoke.
Another common use is to extend and existing, native, C++ code base with .Net library calls.
Just be careful that you partition your code well as it can be quite subtle sometimes in compiling your pure C++ code down to IL transparently!
As to your sidenote: PInvoke is a particular type of Interop. Interop comes in other forms too, such as COM Interop. In fact, more accurately, PInvoke is a set of language features that make Interop with native code easier.
I've used Managed C++ (the .NET 1.1 precursor to C++/CLI) effectively in the past. I find it works best when you have a native C or C++ library you wish to use in managed code. You could go the whole Interop/PInvoke route, which makes for some ugly C# code and frequently has marshalling issues, or you could write a managed C++ wrapper, which is where C++/CLI really shines.
Because C++/CLI is managed code, you can call it from C# (or VB.NET if you lean that way) in the normal way, by adding a reference to the .DLL. No marshalling, no dllimport, nothing goofy like that. Just normal project references. Additionally, you get the benefit of static linked libraries if your native library is so designed, which is a Good Thing (tm).
Phil Nash really hit the big things. Here's one more that I've hit more than once and is the primary reason I've used C++/CLI in the past:
Some applications are extended by checked all DLLs in some location for exported functions with a particular name. In C#, there's no way to declare a native C-style export, but you can in C++/CLI. I create a "wrapper" in C++/CLI that exports the method, handles any translation of C structs to managed objects and passes the call on to an assembly written in C#.
There are certain types that are not available to other languages, such as templates,
const and tracking handle of boxed value types.
templates are specialized at compile-time. generics are specialized at runtime. Although CLR should cache generics specialization for future use (so you get the same List each time you use it), there is still a performance hit each time a generics specialization is requested.
i know other languages discard the const attribute, but have compile time checking in your C++ code is better than nothing.
Having a type like int^ allows you to access the memory on the managed heap directory without unnecessary unboxing. This can help performance when passing tracking handles of boxed values to functions that expect a tracking handle, such as Console::WriteLine(Object^). Of course the early boxing initialization can not be avoided. In other languages you can store the reference in an Object variable and pass it around to avoid unboxing, but you lose the compile time type check.

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