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how do i use C++ code from within C#?

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I want to be able to use all my engine routines from with C#. The engine is in C++ so I need a way to access the engine functions without having to rewrite everything in C# is that possible? and how. Also, will using C++ DirectX in C# be a problem? (if the above is possible that is) thanks.

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If you''re engine is written in managed C++ (or you can convert it to managed C++) you can easily use the features of .Net to use classes from your C++ engine in your C# program.

You can use DX in C# but you have to use managed DX which is different to the normal COM version you would use in C++ (how much different I don''t know).

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Just compile your C++ engine with the /CLR flag as a .dll (if /CLR can handle .dll''s) and access the .dll in C# by adding a reference to it (in VS.net or #Develop, don''t know about other IDE''s interface/name for it)

If /CLR doesn''t work with a .dll, you can just compile it into a regular Windows .dll and import functions from that.

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there are 3 or 4 ways i know, but none work for just 100% pure C++ that you aren''t able to port at all ... here''s what I know about:

1. If you are compiling it, compile it into a .NET assembly ... then any .NET language can use it. Of course this is fairly restrictive because of what can and cannot be compiled in .NET managed code.

2. If it uses COM, then you can access it using using the COM interop features of .NET, just load up your components and off you go ... of course, only the COM components and interfaces are available this way ... but it is often enough for COM based systems.

3. If your functionality is contained in functions using export "C" and being exported by a .dll file, then you can use them from C# very easily, by simple creating a C# wrapper file with 2 lines per function, the first line is the DllImport attribute, and the second line is the C# function prototype that matches the signature of the C function you have. This is how most OpenGL wrappers and such work, download the C# NEHE lesson 1 or 2 for an example.

4. There might also be some P/Invoke way to do it, but probably only if you''ve written the functionality as a callable process / dll, not just functions.

good luck, and report back whatever you find out and use when you do ... thanks.

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quote:
Original post by Xai
1. If you are compiling it, compile it into a .NET assembly ... then any .NET language can use it.


Just compiling any old C++ app with the /CLR switch won''t do you much good. Yes, it will generate MSIL code into a .NET assembly, but that assembly won''t really have many, if any, types that are usable from another .NET language.

The "usual" way, if you''re going to use MC++, is to write a wrapper assembly in MC++ that links to your existing C++ codebase, but creates a set of managed types that exports its functionality.

Sam Gentile has a couple of articles covering this topic: http://www.oreillynet.com/pub/au/1070

quote:

Of course this is fairly restrictive because of what can and cannot be compiled in .NET managed code.


Well, the C++ compiler will happily compile anything that is valid C++ that you throw at it, even with the /CLR switch. Some constructs cannot be compiled to MSIL, such as inline assembler, but in those cases, the compiler will just emit regular x86. The Gentile articles mentioned above has some stuff on this as well.

quote:

3. ... DllImport attribute

...

4. There might also be some P/Invoke way to do it, but probably only if you''ve written the functionality as a callable process / dll, not just functions.


P/Invoke is the same as what you described in pt 3.

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Xai''s response is right on:

Item 3 and 4 on the list are the same, they''re both using Platform invoke, or P/Invoke).

Assuming you don''t want to compile your game engine as a manged assembly, and that you don''t have a COM interface defined on it, then Platform Invoke (i.e. P/Invoke) is the way to go:

You just define a method signature for the name of the method you want to call, and use the DllImportAttribute to define which DLL it comes from, i.e.:


[DllImport("User32.dll")]
static extern Boolean MessageBeep(UInt32 beepType);


Then you can use that method as any other method in C# and it will marshall everything across the native / managed boundry.

Here''s an article that explains it in more detail. Or you can search on google for "P/Invoke".

Incidentally, it does work for 100% pure C++. DLLs are 100% pure, but what I think Xai means is that you have to export your functions from a DLL. The reason for that is because you must define the interface for your DLL so that other programs can correctly get the offset and hookup the v-table to call into your function. Also, without specifying ahead of time, C++ is liable to munge the name of your function, which makes it difficult to call from an outside program. This is all a C++ specific, you''d have the same problems if you''re trying to call into a DLL from a native app.

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thanks for the replies and article links guys. From what I''ve read so far, it seems that the best way would be to make containers for the classes i need to use in C# and compile in managed c++.

The articles Arlid Fines referenced were perfect.

The P/Invode method seems a lot easier though, but I dont see how i can import entire classes from my DLLs and use them, the articles and examples use P/Invoke on normal functions. Can I use it with classes?

by the way, does it make a difference if my classes are using COM interfaces when creating managed wrappers and using them in C#? Or is it only when I actually implement COM interfaces that the methods of wrapping are different?

So can I also wrap my d3d classes in managed wrappers and call those from C# or do i have to reimplement all my d3d functionality using the dx assemblies?

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Hello,

I had the same problem, and with the help of http://www.codeproject.com/csharp/dyninvok.asp?df=100&forumid=2892&exp=0&select=323264 found a solution...



using System;
using System.Runtime.InteropServices;

namespace WindowsApplication1
{
public class CGfxManager
{
[DllImport(@"GfxEngine.dll",
EntryPoint="?CreateCGfxManager@@YAPAVCGfxManager@@XZ",
CallingConvention=CallingConvention.StdCall)
]
public static extern IntPtr CreateCGfxManager();

[DllImport(@"GfxEngine.dll",
EntryPoint="?UnloadScene@CGfxManager@@QAEXXZ",
CallingConvention=CallingConvention.ThisCall)
]
public static extern void UnloadScene(IntPtr _this);

[DllImport(@"GfxEngine.dll",
EntryPoint="?BeginRender@CGfxManager@@QAEXXZ",
CallingConvention=CallingConvention.ThisCall)
]
public static extern void BeginRender(IntPtr _this);

[DllImport(@"GfxEngine.dll",
EntryPoint="?EndRender@CGfxManager@@QAEXXZ",
CallingConvention=CallingConvention.ThisCall)
]
public static extern void EndRender(IntPtr _this);

[DllImport(@"GfxEngine.dll",
EntryPoint="?Initialise@CGfxManager@@QAE_NPAUHWND__@@@Z",
CallingConvention=CallingConvention.ThisCall)
]
public static extern bool Initialise(IntPtr _this, IntPtr hWnd);

// Pointer to the C++ class

public IntPtr _this = IntPtr.Zero;

public CGfxManager()
{
_this = CreateCGfxManager();
}

public bool Initialise(IntPtr ptr)
{
// ptr = handle

return Initialise(_this, ptr);
}

public bool Draw()
{
BeginRender(_this);
EndRender(_this);

return true;
}


public void Dispose()
{
Dispose(true);
}

protected virtual void Dispose(bool disposing)
{
if(_this != IntPtr.Zero)
{
_this = IntPtr.Zero;
}
if(disposing)
{
GC.SuppressFinalize(this);
}
}
}
}


We cannot call the constructor of the class from within the C# class, so we have to create a function within the C++ DLL to do this for us. Same with the destructor, although in this example I have not implemented this.


__declspec(dllexport) CGfxManager* CreateCGfxManager()
{
return new CGfxManager;
}


To find the EntryPoints of the functions, I used the program called Dependency Walker http://www.dependencywalker.com/




Regards,
bangz,


[edited by - bangz on June 4, 2004 1:32:48 PM]

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