I am an experienced .Net programer, but have not compiled a C/C++ program in my life. Now I have this C-dll, headers and documentation (3rd party, not from Win API), from which I need to call about ten methods.
I was thinking of using Platform Invoke. I found these three tools that would create the code for me:
PInvoker: http://www.pinvoker.com
P/Invoke Interop Assistant: http://www.codeplex.com/clrinterop
P/Invoke Wizard: http://www.paulyao.com/res/pinvoke/pinvoke.aspx
and possibly
Swig: http://www.swig.org/
Pinvoker seems to have a bit different approach than the Interop assistant and the Wizard. Swig I just found when checking that this question has not been asked here.
What are the pros and cons of these tools?
What would be the best = easiest and safest way for me to produce the P/Invoke code given that I don't know much about C/C++?
See http://dotnetperls.com/dllimport-interop for an interop example, and this MSDN article for more info. The bible for this stuff is Adam Nathan's book.
Basically you will need to identify the functions in the DLL you want to call. These need to marked with extern to make them accessible to the outside world. The next step, which can get tricky is writing a DllImport for the function. This needs to map between the managed and unmanaged worlds. You will need to work out how to marshal any complex data structures from the C dll into managed code.
You should check to see if there is any sort of COM interface to the DLL. Make sure you really need to use P/Invoke first.
SWIG was originally for wrapping C/C++ code for use from scripting languages. It generates C# code from an interface description (see tutorial). I wouldn't recommend using it from C# if P/Invoke is an option.
if the signatures of the functions are simple then it should take 10 minutes to setup - ie if they take 2 char * and return an int. Its only once they get complicated that it gets messy
The bible on pinvoke is Adam Nathans - .NET and COM: The Complete Interoperability Guide
And I agree with other poster - swig is not the right thing
Related
I'm working on a C# project at the moment and I have zero experience with C#.
We have a set of DLLs written in C++, they have the same classes and same functionality, but they work differently. As an instance let's say our program converts BMP files. We have DLLs for converting BMP to JPG, BMP to PNG and so forth.
Our program which is written in C# somehow should wrap those DLLs, but not in a static way. We'd like to be able to change the DLL in use during runtime, and add new DLLs when need be (also during runtime). Like plugins, if you will.
What would your suggestion be to implement this approach?
This looks good: http://blogs.msdn.com/b/jonathanswift/archive/2006/10/03/dynamically-calling-an-unmanaged-dll-from-.net-_2800_c_23002900_.aspx
If you don't know what all of your DLLs are ahead of time, you will probably need to call the Win32 function "LoadLibrary" "GetProcAddress" and "FreeLibrary." As far as I know, c# does not have a way to do a sort of Dynamic PInvoke automatically. See this blog post for more info
Alternatively, you could create a C# wrapper for each of your DLLs using PInvoke and then use managed delegates to call the functions. Then, by changing the delegate, you can call a different function (presumably in a different DLL) at runtime. This would depend on you having a complete list of the DLLs you intend to use at compile time. It is quite a bit more robust than the first option though. It's also a thousand times easier to let the runtime handle all of the marshaling for you. See this MSDN article for more information.
If they are already in C++, I would opt to write the managed assembly in C++.
This walkthrough could be a starting point. Especially the C++ guy does not need to learn C#.P/Invoke is a little bit slower, but the deeper issue is for you the version management as P/Invoke will lead to runtime-exceptions and not compile errors in case of changes.
You could use extern and DLLImport like facilities provided by Microsoft, For more details Go here or Here
I need to create a VC++ wrapper in C#. Is there a way to automatically generate the code?
Edit: let me clarify a bit: I have a simple project with complicated math functions (computing magnetic declination) in c++. Its just three files, one header, one command line controller and the library.
I was looking at SWiG but I found it to be enigmatic :P. I'm taking a look at C++/CLI.
Any tips and pitfalls to watch for?
Take a look at: Using Unmanaged C++ Libraries (DLLs) in .NET Applications
Or you can use C++/CLI
SWiG supports C#. But a C++/CLI wrapper will be much more ".NET-like" than one automatically generated by SWiG.
You can have a look at this tutorial:
http://www.codeguru.com/csharp/csharp/cs_data/article.php/c4217
I think it's better if you make your own wrapper than using any tool (if it does exists). The reason is that you can create a better C# wrapper using the right philosophies instead of generating a list of function call from a DLL.
And for the pitfalls, the only thing I can say is that since you are going to mix manage and unmanaged class, be sure that your struct/parameters are matching (sizeof or types).
As for most short questions: It depends on your settings and requirements! ;-) If you have a more C style interface, you might be able to solve your problem just by using Interop. If "real" OO progamming and C++ are involved, you probably have to look at C++/CLI. That can be easy, but it can also become painful - depending on your classes. As far as I know, there's not automatic code generation tool.
I'm just looking for a best way to re-use code written in c#, in my c++ projects. Creating a com\service doesn't look like a best option for my needs. How difficult it is to export c# code into a dll and use it in c++? can i get some suggestion or example? is this usual requirement or ? Please help me.
i use win7, VS2008, win7sdk
Thanks & Rgds, ~calvin
Executing managed code from an unnamaged executable is possible, though not quite easy. You can look into this article for an introduction and this book to go further.
I personally would avoid this kind of things in most cases and, if possible, switch the C++ project to C++/CLI to obtain an immediate compatibility with .Net assemblies for a minimal cost.
You can't export C# code into a native dll afaik. At least without very much pain in your buttocks. You should have thought beforehand and write the reusable part in C, thus creating a native DLL which could be used from all languages.
Also, you could try managed C++ - I personally hate it... but there you go
In case you need to use code written in C# C++, then you need to first see what all data types you would be passing from your C++ code to C# code.
1. Basic data types like int, enum etc can be passed from unmanaged to managed code.
2. in case you want to pass on class object, than you need to use marshalling.
If you can't use COM (if the .NET code is already written for example), then you can host the CLR, but this is a long road...
See these other articles
How to load CLR into process and Create a C# DLL That Can Be Imported in a Delphi App Using stdcall - Possible?
I have a DLL made in C#, this DLL contains some clases like Creator.
I need to load this DLL and use Creator class in C++ unmanaged,
so Is there some way to create that instance or must I load just the functions exposed?
I need something like this:
CreatorInstance->Init();
Is this posible?
Most of what you need can be found here: http://msdn.microsoft.com/en-us/library/x0w2664k%28VS.80%29.aspx
Primarily, you need to learn about the /clr switch for C++ compilation. Then you need to understand the C++ extensions that Microsoft added to allow for mixed assemblies. (A C++ "pointer" to a managed class would use p^ instead of p*, and so on.)
John Fisher's approach using C++/CLI is by far the easiest means of handling this, but it is not the only means.
The other three options are:
1) Use COM interop to wrap the .NET class via COM
2) You can host the CLR in your native, unmanaged application, and call into it. For details, see this article.
3) You can host the Mono runtime, and use it to call your managed code. For details on this, see this page.
Option 2 and 3 are very similar, but IMO, 3 is easier than 2.
Here is an interesting article on how you should be able to accomplish this without using the /CLR option
http://www.codeproject.com/KB/cs/ManagedCOM.aspx
Works pretty well.
First of all, it is possible and you do not "have" to use CLI or the /clr switch. Using the good old COM architecture you can do it pretty easily http://msdn.microsoft.com/en-us/library/zsfww439.aspx. Understanding the way COM works might be the biggest challenge here, but it's usefull once you know it.
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#.