I have a scenario where a C# library is consuming a mixed mode C++ library. The use case is as follows:
1) The C# code initializes a listener from the library (managed c++), which initializes a listener from native C++.
2) The native code receives a message and parses it, then passes it to the managed c++ via IJW code
3) The managed c++ calls a delegate from the C# code with the message
This all works fine, except for the very last part - actually including the message. The C# code can't access the data type defined in the managed C++. When you navigate to the struct's definition, it looks like this:
namespace NativeWrapper
{
[CLSCompliant(false)]
[NativeCppClass]
[UnsafeValueType]
public struct MyDataType
{
}
}
As you can see - it decries it as unsafe and wipes out the fields. I've seen solutions to this problem where a third library, in C#, declares a struct, and both the C# and the managed C++ use it. I imagine that would work, but I'm trying to avoid creating a third library for one small file...this component is part of a large system, I'd like to keep the number of DLLs I'm adding to it as small as possible.
So, the question is, is there a way I can define a struct in managed C++ that the C# code can references? I know how to define a ref class, that's how my listener is set up, but I'd like this to be a struct.
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#
My friend build an application ( console app) in C++/CLI.
I'm programming in C#.
Ive build for him some DLL in C# which does some calculations based on params that he send.
My function (inside my C# dll) looks like this :
bool LongCalc(dynamic obj)
{
...
}
(again , the obj needs to be sent from his c++/cli to my c# dll).
my question :
If he creates an object in his cpp like :
cppObj
{
prop1 , prop2 , prop...n
}
would I be able to read his obj in my c# as :
obj.prop1
obj.prop2 .... ?
what should he or me need to do in order for me to work with his obj ?
If he's using your C# DLL from his C++ application then I'm guessing he's using managed C++. If that's the case then it'd make sense for him to define his C++ class as a managed C++ class so that you'll be able to invoke methods against it.
The answer highly depends on how your friend is consuming your C# dll.
If he's using plain C++ and consuming your .NET assembly through .NET COM Interop, then I don't think a dynamic parameter will be supported for a plain C++ class like CppObj from your example, becuase there is no way to know how to invoke the object's methods during run time.
In order for this to work with a dynamic parameter in the C# side, the C++ class will probably have to be a COM object and implement IDispatch, so that the CLR will have the ability to dynamically invoke methods on the C++ object.
I'm not 100% sure that dynamic actually supports IDispatch in COM Interop, but I see no theoretical reason why it shouldn't.
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'm attempting to consume a dll written in C++ from a C# application. I have 3rd party source code for the C++ dll (the Cyclone physics engine) and do not want to manually port it over to C#.
In the C++ project
I changed it to output a dll. I changed it to use the /clr flag. I changed it to use Multi-threaded Debug DLL (/MDd) because that was the only one compatible with /clr and also compiled.
In the C# project
I added a reference to the dll. I'm using the cyclone namespace.
At first there was absolutely nothing under the namespace. I think this is because in the C++ code, all classes were declared with no access modifiers and the default is private. So for the class "Particle" I changed the definition to:
public class Particle
{
//...
}
Now I can successfully declare a variable of type Particle from the C# code. However, intellesense and the object browser report Particle to be a struct (?) and it doesn't contain any methods at all. The c++ code declares a bunch of methods after "public:" access modifiers so I don't know what the problem is.
For example,
public:
void integrate(real duration);
What am I doing wrong?
The Particle class is not a managed class, hence it is treated as a struct. You need to use the ref keyword to make it managed and garbage collected. You also need to do the same to every other class that references it which might be a problem. The best solution I think, is to create a managed wrapper class that uses the Particle class internally. This wrapper class can then be referenced by .net.
See here:
I have not actually run into your exact problem before, but I have used C++ dlls in c# before. Typically when calling a dll like that you would use the dllImport keyword. Basically you can define a class that imports all the types and methods from the c++ dll. You can then call those wrapper classes.
I am far from an expert on it, but I have used it to get access to win32 methods and some other libraries that I needed to use.
This link on codeplex has a few links tools that might help. But the most important is probably the Interop Assistant. It can generate the C# wrappers for your c++ dll.
This isn't exactly what you are asking, but I thought it might help to look at a different direction.
Try declaring the c++ class with the ref keyword:
public ref class Particle
Do you have a reference to COM Interop?
I have added a C# DLL into a C++ project as mentioned at MS support, however I was not able to access its variables and methods inside the class. It also says that it's a struct and not a class, I don't know if it is important but I thought I should mention it is as well. Whenever I write . or -> or :: after the object, nothing appear. But it appear at the name of the class only although they are not static.
Starting with Visual Studio 2005, you can use C++/CLI, Microsoft's ECMA-approved C++ dialect that allows using managed and unmanaged code together. In VS2005, there are the "Managed Extensions for C++", with which you can achieve roughly the same, but you have to use horribly-looking syntaxes for writing managed code in C++ (with lots of double underscores).
With C++/CLI, you can mix managed and unmanaged code in your project, and use C# types directly. IMHO, that's a lot easier than using COM.
To increase compatibility I don't export a class from my DLLs (C# or C++). Instead I expose the class's functions, but the first parameter of each function is a pointer to the class itself. Of you could you also need to expose a: void* CreateMyClassInstance(), and a: DestroyMyClassInstance(void* pInstance).
Read the article posted on below link
http://www.codeproject.com/KB/cs/InterOp.aspx
I think it would help you out.