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#
Related
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 have an unmanaged (C/C++) DLL which I need to call from a C# application.
The DLL call needs to return data (from a C++ class that is created by the DLL) to the C# application.
I have control over the DLL's exported function, so I can create a wrapper around the C++ class if necessary. I know how to access the DLL with p/Invoke, so I'm just looking for some guidance on how to return the data.
The data that is received from the DLL is a series of key-value pairs, so I was thinking about returning a JSON string and deserializing it to an object with Json.NET.
What is the preferred way to access this type of data from an unmanaged source from a C#/.NET application?
If you're able to modify the C++ DLL then C++/CLI could be cleanest. You'll be able to write a set of .NET wrapper classes directly in C++, avoiding the need to write separate P/Invoke declarations.
There is no real reason to add extra layers of serialization just to transfer code between managed and unmanaged applications. But if it would be simpler for your code and you aren't worried about performance than any way you can move data from one layer to another is perfectly fine.
If you want to try the PInvoke way here are a few resources from MSDN...
DllImportAttribute
Platform Invoke Tutorial
This question might seem a repeat of previous ones. I have read through a series of posts, but not completely clear for my situation.
I have a c++ library which is created using momentics IDE. I have to be able to use this library into a c# project.
Someone had been working on this project before being handed over to me. Currently, there are 2 layers for making this possible. First, a c++ project includes the complete library with a c++ wrapper. This project creates a dll as the output. This c++ dll is then fed to a c# project, which has dllimport calls to the c++ dll. This c# project again creates a dll. Finally, in order to use the library in c# application, I have to include a reference to both of these dlls.
Is this the correct way to get it working? I was thinking probably there should be a way to simplify the process.
Can someone please help me with this question?
Given that you're using a C++ library, I'm assuming it takes advantage of C++ semantics like classes, rather than just exposing procedures. If this is the case, then the way this is typically done is via a manually-created managed C++ interop library.
Basically, you create a managed C++ library in Visual Studio, reference your existing C++ library, and create a managed wrapper around your existing C++ classes. You then reference this (managed) C++ assembly in your C# project and include the original (unmanaged) C++ library in your C# assembly just as a file that gets placed in the build directory.
This is required because there is no way to reference things like C++ classes via P/Invoke (DllImport) calls.
If your base library is just a series of functions, then you can reference that directly in the C# project via P/Invoke functions.
Either way, all of the libraries mentioned above (for the first, the unmanaged C++ library, the managed C++ assembly, and the C# project, or, for the second, the unmanaced C++ library and the C# project) must be included in any project that references them. You cannot statically link the unmanaged library into the managed assembly.
Seems like you have one wrapper too many but perhaps someone is implementing some sort of facade or adding properties or something. The basic connection between managed and unmanaged will be either DllImport of "flat" function calls - not member functions - or C++/CLI code calling member functions. If the wrapper is C++/CLI it's easiest to write (just include the header for the C++ library) and easiest to call (C# code just adds a .NET reference to it and carries on as normal) so it would be my first choice if there's C++ expertise on the project.
It sounds like whoever you were taking over from is doing it the hard way. If there are less than 20 methods, I would suggest starting over.
You can use:
DllImport
class Example
{
// Use DllImport to import the Win32 MessageBox function.
[DllImport("user32.dll", CharSet = CharSet.Unicode)]
public static extern int MessageBox(IntPtr hWnd, String text, String caption, uint type);
static void Main()
{
// Call the MessageBox function using platform invoke.
MessageBox(new IntPtr(0), "Hello World!", "Hello Dialog", 0);
}
}
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?