I'm trying to find a tutorial on creating a C++ class in a DLL that can be called from C#. I've found a few tutorials but they either do not compile in VS 2013 Community or are not on point. The C++ object has only a few exported functions (i.e., that are called from the consuming C# app like ptr->StartAction()). It has about 70 procedures that are not exposed, in assembly language which is why I need to use C++. Currently I expose some functions in the DLL via dllimport etc. But C# requires using fixed(...) (to prevent garbage collection) which slows everything down quite a bit (and they are called 1,000,000s of times). Hence the need to move all that into the DLL. So I need a class that I can instantiate in the C# calling program and then call the public methods in the dll. I'm using .NET 4.0. The DLL will only be used by this one C# app.
You can achieve it through the help of COM component and IDL with an output of Interoperability dll where you can use in your c# project. For more details follow this link.
You can use the DllImport attribute of C#. Here is a sample signature:
[DllImport("path to dll", CallingConvention = CallingConvention.Cdecl)]
[return: MarshalAs(UnmanagedType.BStr)]
public static extern string methodName(string parameterName);
C# will call the method with the same name in the DLL.
Its impossible to say what you really need, because we don't have your method declarations.
Related
A third-party app I have can call extension DLLs if they have C-compliant interfaces as described below.
I would like the third-party app to call my C# DLL, since I would rather write in C# than C. (Maybe my other choice would be to write a C DLL wrapper to call my C# DLL, which is an extra step that I might not get right).
I've searched the net and SO but haven't found (or recognized) a good match to my question.
The best suggestion seemed to be this special marshalling declarations in the C# code here: Calling a C# DLL from C; linking problems
Is it possible to write a C# DLL that has a C-compliant interface like the one below? If so, could someone tell me what I have to do or point me to some documentation?
The third-party app documentation says, "The DLL function must be a PASCAL function that takes a single LPCSTR (long pointer to a constant string) argument. C or C++ DLL functions called must have prototypes equivalent to:
extern "C" __declspec(dllexport) void __stdcall fn(LPCTSTR szParam );
Take a look at this article: https://www.codeproject.com/Articles/12512/Using-the-CDECL-calling-convention-in-C-changing
It discusses a different problem (opposite to yours) but also explains the linkage of C# functions - by default C# uses __stdcall (and it cannot be overridden). This means your third party app should be able to call the C# function as it stands. Have you tried it? Did you get any errors?
I have a plugin written for a C++ program (as a .dll). The interface this .dll relies on is something like the following:
class Platform
{
virtual bool callSomeFunc() = 0;
//etc.
}
The .dll provides the platform with an object through an extern "C" function. Pretty standard. The .dll can interact with the platform via an object of a class implementing the above interface. Pretty standard I guess.
Now we have a need to write the platform in C#. Ideally without rewriting the plugin because we have most of our code in plugin. Is there a way to go about this? (Something like passing a C# object for the Platform object the .dll expects?)
If you wish to implement an object in the C# code that the unmanaged code can use, then you can no longer use a C++ class. Only C++ code can create C++ classes. C# code cannot.
The obvious thing to do is to use COM for your interop. The C# code can both implement and consume COM objects.
I have a small C# class (Gram.cs) and it is working with a 3rd party dll to operate a device. Now, I need to call some functions in this C# class using C++.
How can I do it?
I am using MS Visual Studio 2010 professional edition.
If C# class is small, and it deals with native dll, it might by simpler rewrite that class in C++, rather then integrate .Net into your application. In addition, integrating .Net will force whole .Net virtual machine to start just for processing your simple class.
Otherwise,
You could use COM interop: build an assembly based on your C# class and make it COM visible. Then you could use class as a COM-object.
You can use Managed C++ to make a wrapper between managed and unmanaged code.
You can reverse control flow, so C# code will call unmanaged functions. In this case you can export it from your binary and import from C# code with DllImport attribute.
Normally you should make your c# code as COM visible from your c# project settings and use c# IJW regasm tool.
Look into http://msdn.microsoft.com/en-IN/library/ms173185.aspx
I had integrated c# into c++ using this approach few years ago.
You will be able to load your c# assembly as a COM component in your c++ code.
This might be what you're looking for (I've answered similiar question here before: how to : use c++ projects for windows phone (C#))
a) Load symbols directly from C library, for example:
using System;
using System.Runtime.InteropServices;
static class win32
{
[DllImport("kernel32.dll")]
public static extern IntPtr LoadLibrary(string dllToLoad);
[DllImport("kernel32.dll")]
public static extern IntPtr GetProcAddress(IntPtr hModule, string procedureName);
[DllImport("kernel32.dll")]
public static extern bool FreeLibrary(IntPtr hModule);
}
(this is taken from: http://www.andyrushton.co.uk/csharp-dynamic-loading-of-a-c-dll-at-run-time/ after brief googling)
You need to export the C++ interface methods as "C" for that, e.g.:
extern "C" __declspec( dllexport ) int MyFunc(long parm1);
(from MSDN: http://msdn.microsoft.com/en-us/library/wf2w9f6x.aspx)
b) Use a wrapper in C++/CLI to connect unmanaged C++ to managed C#:
here's a good example: http://www.codeproject.com/Articles/19354/Quick-C-CLI-Learn-C-CLI-in-less-than-10-minutes
Do note that the syntax is somewhat weird at first look, and not eveything can be used. However, what you gain is ability to use the C++ classes - something that exporting "C" prohibits you from doing.
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 have a C++ class I'd like to access from a C# application. I'll need to access the constructor and a single member function. Currently the app accepts data in the form of stl::vectors but I can do some conversion if that's not likely to work?
I've found a few articles online which describe how to call C++ DLLs and some others which describe how to make .dll projects for other purposes. I'm struggling to find a guide to creating them in Visual Studio 2008 for use in a C# app though (there seem to be a few for VS 6.0 but the majority of the options they specify don't seem to appear in the 2008 version).
If anyone has a step-by-step guide or a fairly basic example to get going from, I'd be very grateful.
The easiest way to interoperate between C++ and C# is by using managed C++, or C++/CLI as it is called. In VisualStudio, create a new C++ project of type "CLR Class Library". There is some new syntax for the parts that you want to make available to C#, but you can use regular C++ as usual.
In this example, I'm using std::vector<int> just to show that you can use standard types - however, in an actual application, I'd prefer to use the .NET types where possible (in this case a System::Collections::Generic::List<int>).
#pragma unmanaged
#include <vector>
#pragma managed
public ref class CppClass
{
public:
CppClass() : vectorOfInts_(new std::vector<int>)
{}
// This is a finalizer, run when GC collects the managed object
!CppClass()
{ delete vectorOfInts_; }
void Add(int n)
{ vectorOfInts_->push_back(n); }
private:
std::vector<int>* vectorOfInts_;
};
EDIT: Changed the class to hold the vector by pointer instead of by value.
If such DLL is unmanaged. You will have to use P/invoke. A p/invoke function definition looks like this:
[DllImport("Library_Name.dll", EntryPoint = "function")]
public static extern void function();
If, on the other hand, is a managed (C++/CLI) DLL (or assembly). You can access it by adding a reference to it on your .NET project.
EDIT:
I think I didn't answer your question at all. But to create a managed C++ DLL to be accessed from .NET, create a new project an choose:
Visual C++/CLR/Class Library. And then, just add its output DLL to your C# project.
That'd do it. :)
Do you have an existing C++ exe that you want to re-build as a dll? Or is all you have the C++ class?
If all you have is the C++ class, you might think about building a .Net dll. While you couldn't pass stl types from C# to C++, I am pretty sure you can pass managed .Net types.
If you must use the stl types in the class, you could convert the data in the C++ class, or the calling app.
I've found a tutorial which works. A quick note though, you have to be careful to copy the .dll into the same directory as the executable. I messed around with trying to tell the executable where the DLL was but gave up in the end.
Use of unmanaged C++ Dlls can be very tedious in C#.
An "easier" route is to place it in a COM wrapper.