In Mono you can pass a delegate from C# to a C++ function which takes in the delegate as a function pointer. Can this be done in C# on Windows for example where you can compile a native C++ unmanaged library, link it against a C# project and get a C++ function to invoke a C# function via a function pointer which C# passed to it as a delegate?
Define a delegate in .NET, and then pass that to your unmanaged code. The CLR will expose the delegate as a function pointer which you can call from your unmanaged code.
The interop layer does not know how to handle references in C++. So You need to expose the object as a pointer, not a reference. Additionally, .NET doesn't know what a C++
object is (it's not the same as System.Object). That will need to be passed
as an IntPtr, and I don't think there is much you can do with it in .NET.
C++ callbacks:
typedef void (*CBFUNC1)(unsigned int, const char*, object&);
typedef object* (*CBFUNC2)(object*, struct _mystruct* );
C# signatures for the delegates would be
delegate void CbFunc1(uint param1, [MarshalAs(UnmanagedType.LPStr)] string
param2, IntPtr param3);
delegate IntPtr CbFunc2(IntPtr param1, ref _mystruct param2);
One option you have is to use C++/CLI to call into the C# code. If your C++ code must stay unmanaged (native), then you should wrap your C# code in a COM component and use it from your C++ code.
This obviously can be done - all CLR hosts are native applications to start with. Your options:
in managed application call your native DLL (PInvoke)
call managed COM object (as Dan suggested)
host CLR yourself - sample
You are looking for Marshal.GetFunctionPointerForDelegate().
Rohit's answer is right, but there are lots more gotcha's on the path depending on whether you're calling back immediately (C# calls C++ which calls back C#) or if you want to call back repeatedly (C# calls C++ and after returning calls back one or more times later to C#).
i wrote this example from the perspective of Unity/C# and C/C++/Objective-C interop, but you may find some of the comments and code-snippets useful no matter where you are doing C#/C interop.
in particular make sure that you're propertly retaining/holding any delegates you pass from C#/managed to C/unmanaged code if the C/unmanaged code might be calling back at a different time.
Related
I currently have a large C++ library that I need to incorporate into a C# project. I was successful in using DllImport to get access to some functions from my library, like this:
[DllImport("MyLib.dll")]
public static extern int SampleFunction(string param);
However, I can't seem to figure out how to make it work for functions that either have a parameter or return type that is not defined within the dll itself (i.e., the code in the dll imports it from another file), such as this example function that takes in a list:
[DllImport("MyLib.dll")]
public static extern std::vector<MyClass> MyFunction(string param);
For std library functions, I know I can get the dll and import that in, but what about other classes like MyClass in the above example? Do I need to create a managed wrapper class in C++ for each of these classes, or is there another way to do this?
std::vector<MyClass>, or indeed any unmanaged C++ class, cannot be used for interop to C#. Indeed, even if you wished to consume this function from another unmanaged C++ module you'd have to make sure that you were using the same compiler and dynamic runtime as the DLL which exported the function.
You'll need to find some other way to implement this functionality. There are lots of different ways to do that.
You could expose a p/invoke interface to the functionality. That would likely involve declaring a struct to represent the data of your class, and serializing to and from that struct.
You might consider a COM interface but it won't offer great advantages over p/invoke. You'd still need to serialize your class.
A C++/CLI wrapper would be yet another option. You'd wrap the unmanaged class with a managed C++/CLI class, and then consume that from the C#.
If you need a custom class from a native lib, you'll probably need to export a type library or use managed C++ to write a wrapper. What you're effectively trying to do is marshal a piece of memory from native to managed and now have to deal with how the data type is marshaled.
If at all possible, I would actually recommend trying to do away with the marshaling as when it works it's fine, but when it breaks, it can be rage inducing to debug.
Regardless, I'm actually not sure if anything in the STL can be marshaled. At the very least, I have never seen it done. More times, I've had to do a conversion like so: How can I marshall a vector<int> from a C++ dll to a C# application?
If you want to marshal an actual class, the standard way I've done it up until now is through a type library: Import TLB into C#
Or by linking a native lib into a managed C++ class and then referencing the managed C++ dll into the C# project as a shim.
Beyond that, if you can convert the class to strict C-style functions and pass a struct around, that could allow you to just use pinvoke, this is no different from simply exporting a bunch of helper functions except you can marshal a struct representation back and forth: Marshal C++ struct array into C#
I have a C++/CLI wrapper for a C++ class which I create several instances of in a C# application, and this works fine, except for the functions in the C++ code which take a buffer from the calling function and fill it with whatever is received a call to recv, similarly some functions take a packet to be sent as a parameter.
In the C++ code there are several structs that define all the packet structures, pointers to which are taken as parameters, and I have equivalent C# structs which are packed in the same way so that they appear exactly the same in memory, what I don't know is what C++/CLI type I can use as parameters for functions that take pointers to C# structs, and can be passed to the C++ code.
Thanks.
You don't need any special “C++/CLI type”, you need just the C++ type. If it is a simple C-like struct (no virtual method tables or anything like that), then you could try using Marshal::StructureToPtr(). If it's not that simple, you probably need to copy it from the C# object field by field.
I want to import an unmanaged C++ DLL and call a function that takes stringstream as a parameter. In C#, there is no stringstream class, so can anyone tell me how to call such a function from a C# program?
You should not expose templated objects via a DLL, period.
Templated objects (e.g. almost everything in std::) become inlined. So in this way, your DLL gets its own private copy of the implementation. The module calling your DLL will also get its own private implementation of stringstream. Passing between them means you are inadvertently weaving two unrelated implementations together. For many projects, if you are using the exact same build settings, it's probably no problem.
But even if you use the same compiler, and mix a release DLL with a debug EXE, you will find stack / heap corruption and other harder-to-find problems.
And that's only using your DLL from another unmanaged C++ exe/dll. Crossing then the lines to .NET is even more of a problem.
The solution is to change your DLL's interface to something that plays friendly across DLL bounds. Either COM (you could use IStream for example), or just a C-style interface like the winapi.
If you can modify the C++ dll, export a plain string version. Otherwise you have to build a managed C++ wrapper project, import the other C++ dll, export it as a managed function, and call that from your C# code. C++ interop really sucks.
I'm afraid that you're going to have to create your own StringStream class in C# in order to be able to consume the functions exported from that DLL. As you mentioned, the .NET Framework doesn't provide any similar class out of the box.
The easiest way is probably to wrap the StringBuilder class provided by the .NET Framework such that it can function as a stream. See this blog post for a further explanation and some sample code.
A similar question was also answered in MSDN Magazine: http://msdn.microsoft.com/en-us/magazine/cc163768.aspx. You might find some of the hints and/or sample code given there useful.
You are trying to bind native C++ code to managed code in C#. Best way of doing that in general is to introduce middle layer in managed C++ that will provide interface to calls from C#.
Create an Wrapper dll in c, or c++ that exposes an friendly call to that function. It's the better way.
for example an
BOOL getString(TCHAR * myreturnString, DWORD *size);
I want to invoke the following C++ function (exported by a DLL) from C#:
void createVm(
const jace::VmLoader& loader,
const jace::OptionList& options,
bool ignoreUnrecognized = true );
I've found documentation for marshaling primitives from C++ to C# but I'm not sure how to handle reference-types or non-pritmive types such as VmLoader or OptionList (both of which are classes). I'm trying to wrap a C++ API with a C# layer, delegating to the underlying C++ code for the actual method implementation.
Any ideas?
AFAIK, PInvoking into a function with C++ constructs is not a supported operation. You could probably get it to work but I think you'll find problems.
What is supported is writing a simple C wrapper function which calls into your C++ function. PInvoke into the wrapper function instead and that will do the trick.
Assuming the c++ DLL correctly exports the types being passed by reference, you could right a light weight managed C++ wrapper that calls the dll. With managed c++ you can call native C/C++ libs and dlls directly while still exporting a managed interface from the resulting assemblies. Other .Net languages can call the managed interface just like they would any other assembly. It's a bit of extra overhead, but's is can be the quickest way to get it done.
I am importing the CreateICeeFileGen() function from the unmanaged DLL mscorpe.dll in a C# application, in order to generate a PE file. This function returns a pointer to an C++ object defined here, is there any way I can access fields from this class via C# or do I need to write an unmanaged wrapper DLL?
The code I'm using currently is as follows:-
[DllImport(#"C:\WINDOWS\Microsoft.NET\Framework\v2.0.50727\mscorpe.dll", EntryPoint = "CreateICeeFileGen")]
static extern void CreateICeeFileGen(out IntPtr iceeFileGenPointer);
...
IntPtr filePtr;
CreateICeeFileGen(out filePtr);
N.B.: I know you can do similar things with .net libraries but I need to use unmanaged libraries for my purposes.
You need a wrapper library to be able to use the class from C#.
The best bet would be to create the wrapper using C++/CLI, which can directly call the unmanaged function and expose the details with a managed class. This will eliminate the need to use P/Invoke for anything.
(Well, technically if you know the class layout you could mess around with pointer arithmetic to access the fields, but this would be very fragile and messy, and trying to call virtual functions in this way would be extremely ugly).
It looks like COM class/interface. Can you not just use COM instead?