I'm trying to read AAF files (that describe edited video and audio sequences) in c#. AAF is open source, and there's a C++ SDK available http://sourceforge.net/projects/aaf/.
I'm a C# coder and while I understand some of the C++ coding paradigms, my C++ is basically non-existent.
I presume the intereaction is possible using pinvoke which I've used before for interacting with Win32. With win32 I've pulled calling information from pinvoke.net, but I'm not entirely sure how I go about defining the pinvoke entry points from scratch with a third party SDK.
Can anyone help me to get started on this? For instance, what are the first steps in pinvoking a third party C++ library? Are there tools for helping automate this process?
You have basically two ways of doing that:
Using C++ Interop (implicit PInvoke)
Visual C++ can interop with native C++ code. So you can use Visual C++ as a bridge between the native C++ and C#. Basically you have to write wrapper (or "proxy") classes in visual C++ to interact with your native C++ objects.
Under the hood, this method uses PInvoke (therefore "implicit PInvoke") with specific options, but it has the advantage of retaining the object-oriented structure of the native C++.
Note that this method is not portable to Mono.
Using good ol' PInvoke
You can use PInvoke with C++ the exact same way as you use PInvoke with C.
There is however a limitation: you cannot PInvoke C++ methods this way, so you lose the C++ object-oriented structure.
If the library that you are using provides a C API, you can use that. Otherwise, you have to create a small C++ wrapper that will wrap the C++ API in the form of C-style free functions.
If you have a lot of classes to wrap this way, you can use SWIG to wrap automatically. As a bonus, SWIG recreates the object-oriented structure in C# via some guru code generation. However using SWIG requires some setup and I don't think it is necessary if you only need a few functions.
Related
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.
Does anyone know of a way to call MIT's Meep simulation package from C# (probably Mono, god help me).
We're stuck with the #$#%#$^ CTL front-end, which is a productivity killer. Some other apps that we're integrating into our sim pipeline are in C# (.NET). I've seen a Python interface to Meep (light years ahead of CTL), but I'd like to keep the code we're developing as homogeneous as possible.
And, no, writing the rest of the tools in Python isn't an option. Why? Because we hates it. Stupid Bagginses. We hates it forever!
(In reality, the various app targets don't lend themselves to a Python implementation, and the talent pool I have available is far more productive with C#.)
Or, in a more SO-friendly question form:
Is there a convenient/possible way to link GNU C++ libraries into C# on Windows or Mono on Linux?
The straightforward and portable solution is to write a C++ wrapper for libmeep that exposes a C ABI (via extern "C" { ... }), then write a C# wrapper around this API using P/Invoke. This would be roughly equivalent to the Python Meep wrapper, AFAICT.
Of course, mapping C++ classes to C# classes via a flat C API is nontrivial - you're going to have to keep IntPtr handles for the C++ classes in your C# classes, properly implement the Dispose pattern, using GCHandles or a dictionary of IntPtrs to allow referential integrity when resurfacing C++ objects (if needed), etc. Subclassing C++ objects in C# and being able to overriding virtual methods gets really quite complicated.
There is a tool called SWIG that can do this automatically but the results will not be anywhere near as good as a hand-written wrapper.
If you restrict yourself to Windows/.NET, Microsoft has a superset of C++ called C++/CLI, which would enable you to write a wrapper in C++ that exports a .NET API directly.
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 need to do some process injection using C++ but I would prefer to use C# for everything other than the low level stuff. I have heard about "function wrapping" and "marshaling" and have done quite a bit of google searching and have found bits of information here and there but I am still really lacking.
Things I have read in order of usefulness;
http://msdn.microsoft.com/en-us/library/ms235281(VS.80).aspx
http://www.drdobbs.com/cpp/184401742
http://geeklit.blogspot.com/2006/08/calling-c-lib-from-c.html
How can I wrap all the lower level stuff (native C++) in C# so I can easily command those functions in a language I am more comfortable with, C#?
Any information on the topic is much appreciated.
I think P/Invoke is really the most straightforward approach:
Create a DLL in unmanaged C++, containing all the functionality you need to do the injection.
In your C# code, declare some static extern methods, and use the DllImport attribute to point them to your C++ dll. For more details, see the link provided by arul in his answer.
Note that P/Invoke isn't limited to "windows API functions" — you can call functions exposed by any native DLL.
A potential downside of P/Invoke is that you will have to provide the signatures for your C++ functions, possibly specifying some less-than-obvious marshalling. In that case, you could consider constructing a COM server instead of a "plain" DLL, and using COM interop to call your code from C#.
You want to use P/Invoke, see MSDN Magazine.
If Pinvoking isn't what you want to do, then create a managed C++ application. Use native C++ to do the process injection stuff. Use managed c++ to create a .NET friendly interface to this native behaviour. This can then be called from C#.
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.