I have a code written in C++ (that I did not write) and want to use it in C#, so I decided to make a dll and use this class from there.
I have very little knowledge of C++ and am having problems referencing the methods of this class in my C# project.
The C++ code is like this:
#ifndef BeamAn_class
#define BeamAn_class
#define DllExport __declspec( dllexport )
#include <vector>
#include <cmath>
using namespace std;
public class DllExport BeamAn
{
public:
BeamAn();
~BeamAn();
bool SetGeometry(vector<double>); //I didn't put the DllExport here because I already did it for the whole class. It's okay to do this, right?
//other public methods an stuff
private:
//private methods an stuff
}
#endif
In my C# project I added the reference to the C++ dll normally (right click on the project, add reference. The .lib and .h files are in the same folder of the dll).
But looks like Visual Studio can't "see" the methods of my class. I can create a object of the BeamAn type, but can't use any of its methods.
For example, I can do this:
BeamAn contBeam = new BeamAn();
But can't use any of the methods or atributes inside the class, like this: contBeam.SetLoadFactors(1.0,1.2);
Visual Studio says that "BeamAn does not contain a definition for 'SetLoadFactors' and no extension method 'SetLoadFactors' accepting a first argument type 'BeamAn' could be found (are you missing a using directive or an assembly reference?)
Is there more something I should write in the C++ code to make the dll work properly, or am I doing something wrong when referencing it? I know that I'd have to use "DllImport" in my C# code if I was explicit linking, but that's not what I want to do.
Thank you very much!
There are several ways to make C++ library available in C#.
Use PInvoke - directly call your C++ code. See this article for more information. Also see pinvoke.net for general reference.
Use an interop language to create a managed wrapper around your unmanaged code. If you're in the Microsoft world I would recommend C++/CLI to create mixed mode libraries (dlls that contain both managed and unmanaged code). Here is a brief (and old) article introducing C++/CLI.
Make your C++ COM accessible. Since the code isn't yours this one might not be useful to you. See this post for more information about C++ and COM.
For simple scenarios PInvoke is probably the easiest. For more complicated interactions of the managed and unmanaged code I would recommend writing a mixed mode dll with an interop language. And if those don't work for you, use COM.
To address the error you receive: you can't add a reference to a C++ library from a C# project - they are completely different languages with different memory management systems, different type systems, different everything (well, a lot of things). Also, you can't pass data structures (like vectors, maps or sets) from unmanaged code to managed code.
to use c++ code in a c# project, you have 2 options:
wrap your c++ class in a managed c++ class
use a library called swig
a link that might interest you: Wrapping Visual C++ in C#
Related
I am trying to access an enum in a C++ class header (.h) from C#. Is there a simple way of doing this? Every example I have seen involves compiling the class into a .dll, which for this example is kind of a waste because the function of this class is pretty limited.
Edit by request: The C++ library CAN be modified. In fact, the C++ library is the major component of the project(firmware) and is developed by other members of my team, the C# (my part) is just for unit testing purposes.
Realistically, you have three options:
Create a glue library that exports a C function (extern "C") that includes this header and returns the enum value you are interested in, then P/Invoke this library from C#.
Hard-code the value in your C# code.
Write a C++ parser and extract the value that way. (Either a complete C++ parser, which would be preferable, or you can be lazy and write a simple regex parser that will work on this particular version of the C++ header, but might break in the future if the code changes in a way you didn't expect.)
In order to access the C++ enum, you have to turn the C++ class into something that .NET can recognise, which either means compiling it as C++/CLI (if that is an option) or turning into a DLL that the .NET interop can access.
Well, this freaks the CS pre-compiler out a bit, but it builds:
#if CSHARP
namespace Test
{
public enum SharedEnum
#endif //CSHARP
#if CPP
typedef enum SharedEnum
#endif //CPP
{
One,
Two,
Three
}
#if CPP
SharedEnum
#endif //CPP
;
#if CSHARP
};
#endif
Just add the Conditional Compilation symbol CSHARP to your C# project, add the existing .cs file and the preprocessor definition CPP to your C++ project.
(credit to Yakk for having the same idea)
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'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.
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.