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.
Related
I am trying to use 7zip from within my application code. On 7zip's website, they say I can use 7z.dll. So, I tried to reference it from C#, but that didn't work. So, I decided to write a C++ library that references 7z.dll, and then I can reference that library from C#.
I was able to load the library (I think) in my C++ library, and I am able to reference that library from C# and successfully call a method.
However, I don't know how to figure out the method names inside the 7z.dll library so that I can call them.
Please help
Hmm, Hans Passant pointed out SevenZipSharp which makes my answer rather useless ;-) I'll leave it for purely educational purposes. No need to write your own COM interop wrappers if somebody else has already done it for you...
I had a look at their C++ example (under CPP/7zip/UI/Client7z). Everything is done using COM interfaces and various types of callbacks.
While C# has excellent COM interop support, it would require redeclaring the relevant COM interfaces in C#, or perhaps using late-bound dynamic magic instead. However, both of these options are rather non-trivial for a project the size of 7z, so on second thought it's likely best to stick with your C++/CLI wrapper approach.
Within that example, you can see exactly how main does it: It loads the DLL (using a wrapper class NDLL::CLibrary around the LoadLibrary call), then obtains a pointer to the COM CreateObject function (via the same wrapper that does a GetProcAddress internally).
Once you have the address of the CreateObject function, you can call it with the appropriate application and interface GUIDs to obtain instances of objects that implement them, after which you can use those objects to do the actual work. The interfaces themselves are declared in header files such as IArchive.h.
We have a COM interface declared and implemented in unmanaged C++. We no longer wish to maintain this assembly, but do need to make some changes, and still be backward compatible.
What I want to do, is to write all the new code in C#, and make it ComVisible. From this thread I see a reference to TreatAs to replace the old interface.
I was thinking along the same path as Jonathan Peppers regarding ProgId, Guid, etc. I will implement the exact interface as the old version as a wrapper to the new implementation. I am also thinking about adding MarshalAs attributes exactly as in the generated interop wrapper to be sure the data types will be the same, if possible.
Are there anything else I should consider while working with this? Anyone with experience doing this conversion?
EDIT: I do have the IDL file for the server. I am not sure if there is a way I can auto generate the code based on this. COM is not something I'm very familiar with.
EDIT Q: How should I deal with HRESULT used by existing clients?
ADDED: Figured I should point other readers to a different fix, which is not available for my scenario as I can't recompile all the .NET applications using the existing com:
Bjørnar Sundsbø
One quick way to get started:
Import your existing COM object into C# with tlbimp (or Visual Studio)
Load up .Net Reflector and get the generated interface to put in your new project
Implement the generated interface in C#
Switch any import declarations to export instead
This should get all your types and method signatures correct from the start. It is a great starting point for porting an existing COM interface to C#.
It seems to be by design to prevent managed COM object from being used from a managed client.
Here are some links to the same problem, as well as this thread, providing some solutions. Also take a look at the answer Jonathan Peppers provided to see how to start out if you only need to use it from unmanaged applications.
The only way I figure I could work around this, is a messy solution where I create the new code in C#, add a COM layer on top of that. Then create an additional COM layer as unmanaged C++ which accesses the first layer so, that my .NET applications can access it.
{Unmanaged COM exposing the original interface} => {Managed COM with rewrite of the original logic of the COM}. All existing applications will then access the "{Unmanaged COM...}". If I get desperate enough, that might be a way. For now I'm abandoning this approach and looking for other solutions.
If you can, recompile your managed application to use the new assembly, do so. You can still use that managed COM from VB6, unmanaged C++, etc. If you still need to reference as a COM from managed, you might be able to create new instances using the approach specified in one of the referenced posts, as long as you don't need to create an interop wrapper.
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.
I just got handed an SDK made of C++ dll, lib, exe, and various .h files. I presume it is meant for C++ developers. The sample projects they provide with their documentation are all written in C++. I am able to spin them up with Visual Studio 8 (2005) and run them. They do control the device as advertised. However the project this needs to be used by is in C# .Net 2.0 and that is unchangeable.
My boss was a C++ developer and says all I need to do is to compile it as a COM object and then import the COM object into my C# solution. My boss says it should take less than an hour to "wrap" there SDK up as a COM object, even for me with no knowledge of C++ compiling.
I've used COM objects in C# solutions before so once this is made, I can continue on from there without a problem.
However, I don't know what to do to make the COM object from the 2 .dll files, 1 .exe, 1 .lib file, 1 .xml file, and the 12 .h files. Is there a resource available to tell me what to do to make this happen?
My boss was a C++ developer and says all I need to do is to compile it as a COM object and then import the COM object into my C# solution.
That's true, however compiling it as a COM object is "difficult" (by which, I mean that you can't do it) unless it already implements the COM APIs (if it doesn't then you need to implement the COM APIs before you can build it as a COM object).
There are books (for example, Essential COM) which explain how to to create COM objects using C++, but it's non-trivial (for building COM objects there may be better books than Essential COM, and better/easier tools than C++).
I think you and/or your boss have 3 options:
Ask the vendor to give them to you as COM objects
Design a COM API that would wrap the SDK's API. Create a COM project (in the language of your choice) which exports this API. Implement these APIs by invoking the underlying SDK methods. To do this you may need someone who knows C++, or be willing to spend much, much longer than "an hour" on this project.
Forget about using COM; instead, build the SDK as a DLL, and use PInvoke to invoke it from .NET code.
My boss says it should take less than an hour to "wrap" there SDK up as a COM object, even for me with no knowledge of C++ compiling.
Based on what you've said I don't know of any way to make that happen.
Tell your boss if it would take him less than an hour to wrap it up, he should certainly do it: it would be a more efficient use of both your time.
I would also suggest ATL (not using attributes), but this is something which can take some time to get right if you're not experienced.
My boss says it should take less than
an hour to "wrap" there SDK up as a
COM object, even for me with no
knowledge of C++ compiling.
That may be true for an experienced C++/COM developer, but not for a beginner. I think your best bet is to use ATL. Take a look at the MSDN tutorial.
And do not use attributes.
This doesn't quite answer your question, but...
One option instead of trying to make a COM object is to use P/Invoke and just call the methods in the DLL.
This thread on the MSDN Forums documents how to make a DLL to call using P/Invoke.
Of course if you need access to a whole class (and make an instance of said object), this isn't going to be helpful.
It's good that the code compiles and runs for you. That said it's totally unfair to assume you can do this in an hour.
Have you checked to see what is actually being built by Visual Studio. There could be a chance that it is already building a COM object.
Investigate how the code is being called. I assume you have a .exe that you can run to test the code. Step through this in the VC++ debugger (it's similar enough to debugging C# code) and try to identify any API calls that match with your docs/expectations. This knowledge will be helpful if you try to go the P/Invoke route.
Something else to consider is SWIG. This is typically used by Python developers to wrap C/C++ code and provides some support for C#.
The managed C++ route is probably more advisable for experienced C++ devs because you need to understand a lot about memory allocation, for all but the simplest code.
I (well, really my lead and I) will first try using p/Invoke (via the DllImport feature of System.Runtime.InteropServices) against the SDK's dll the company provided. I'll let you know how it goes.
I think what you really want/need is C++/CLI, that way you can just build them directly into a managed assembly. The idea is that you write a pretty plain wrapper that looks like kind of a cross between C# and C++ and then it does the rest.
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.