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)
Related
Suppose I have a dll written in pure C. I have an inculde file (.h) so I can use the dll from a VS 2012 C project.
Is there any way to generate a C# wrapper class based on the metainfo in the include file, or I must write all the [DllImport]... manually? The C source code for dll is also available.
(Please note: This is not a COM library)
Thanks in advance
There are tools that can help, but by and large you have to write the wrapper code yourself to some degree. The main reason being that a C header file does not fully specify the interface. For instance, consider this function:
void foo(int* x);
Does this function receive a pointer to a single int, or does it receive a pointer to an array? There's no way for you to tell with just this information. So, any tool that creates wrappers must also use some form of annotation to fully describe the semantics of the functions. If those annotations are not present you would need to create them. At which point it probably becomes quicker and easier to write the wrapper manually.
As an alternative to writing C# pinvokes you can use a mixed mode C++/CLI assembly. This can include the header file and link against the import library. Then all you need to do is write a C++/CLI ref class to wrap the interface, and add the C++/CLI assembly as a reference to your C# project.
The issue is fairly simple, I have some constants in a C++ namespace that I would like to wrap using SWIG 2.0.8. It looks something like this:
namespace Example {
static const float PI = 3.14159f
...
/* Lots of classes are here */
}
Unfortunately SWIG handles this rather awkwardly. In the C# case, it adds the constants to a class with the same name as the namespace so it must be accessed by using Example.Example.PI even when I am explicitly using Example (due to masking by the module name).
In Java, its even worse as it does not treat it as a constant at all and I am forced to call it using Example.getPI() as a method call instead of a constant class variable.
If I move the constants to the global namespace, this seems to work but then the variables must be accessed using ExampleConstants.PI.
Ideally, I would like both languages to be able to access the constants via Example.PI to be consistent with C++. But a compromise that I would be happy with is if I could have a Constants class inside my namespace so that I can use Constants.PI in either language. But of course, C++ does not allow non-integral types to be defined inside a class and this is still not solving the issue in Java.
Is there any elegant way to handle these namespace constants with SWIG?
And if not, is there a way I can manually add a Java or C# class to define them?
I solved similar problem for C++ - C#. I am not sure if this is exactly what you are looking for, but I hope you will find some info useful for you.
I have not touched Java code in my project.
Swig solution.
I created class with public static parameterless functions in C++.
Then I exported them to C# using SWIG.
I specified namespace for C# in command line with -namespace <name> key. More details available at page SWIG and C#
As a result you can impelement solution to access your constant with Constants::PI() and Constants.PI()
Direct solution
If you would like not to use SWIG or other library, you should use PInvoke. There are a lot details and special cases when working with it. Most comprehensive article on subject I have found is Mono Interop with Native Libraries
You should consider JNI for Java.
Note, that C++ functions are exported without namespaces as pure C functions and you should create C# class and create functions with DllImport attribute to wrap functions back to namespaces.
In general if your C++ interface is more or less fixed and/or small I would adhere direct solution, because SWIG layer has many-many specific cases which should be learned along with PInvoke/JNI. But if you C++ interface frequently changed and requires a lot of effort to keep C++, C# and Java consistent, you defenitely need to consider SWIG.
You may find non-trivial example using PInvoke at https://stackoverflow.com/a/11909571/13441
Concerning C++ constants. You can specify C++ constant inside class, refer to C++ static constant string (class member) for details.
I use SWIG 1.3.40.
Hope this is helpful.
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#
How can we export C# methods?
I have a dll and I want to use its methods in the Python language with the ctypes module.
Because I need to use the ctypes module, I need to export the C# methods for them to be visible in Python.
So, how can I export the C# methods (like they do in C++)?
Contrary to popular belief, this is possible.
See here.
With the normal Python implementation ("CPython"), you can't, at least not directly.
You could write native C wrappers around our C# methods using C++/CLI, and call these wrappers from Python.
Or, you could try IronPython. This lets you run Python code and call code in any .Net language, including C#.
That's not possible. If you need DLL exports you'll need to use the C++/CLI language. For example:
public ref class Class1 {
public:
static int add(int a, int b) {
return a + b;
}
};
extern "C" __declspec(dllexport)
int add(int a, int b) {
return Class1::add(a, b);
}
The class can be written in C# as well. The C++/CLI compiler emits a special thunk for the export that ensures that the CLR is loaded and execution switches to managed mode. This is not exactly fast.
Writing [ComVisible(true)] code in C# is another possibility.
(This may no longer be relevant since SLaks has found that ingenious link, but I'll leave an edited version for reference...)
The "normal" way of exposing .NET/C# objects to unmanaged code (like Python) is to create a COM-callable wrapper for the C# DLL (.NET assembly), and call that using Python's COM/OLE support. To create the COM-callable wrapper, use the tlbexp and/or regasm command-line utilities.
Obviously, however, this does not provide the C/DLL-style API that SLaks' link does.
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.