Using a C++ DLL in a C# Project

[BDowling]

Hi all,

I have an existing Visual C++ project that builds a DLL (not COM or
ATL or anything). I wish to use this DLL in a Visual Studio 2005 C#
project without having to define each function and structure again in
the C# project (using pinvoke I believe).

I've done some reading around and it seems that what I'm after is
possible. I've added the old C++ project to my new C# solution and set
the compiler to use /clr. I can then add the DLL as a reference to the
C# project without any errors. However, I'm stuck there. How do I
actually invoke any of the methods in the DLL? Adding "using <DLL
name>" produces an error, and I'm not sure what else to try.

Thanks in advance,

Ben

 

[Nicholas Paldino [.NET/C# MVP]]

Ben,

The dll, does it export functions, or classes? If it uses functions and
structures, then you should not add a reference in your project to the dll.
You will have to make the calls to these functions through the P/Invoke
layer, which will require a re-declaration of the structures and the
functions in your code.

If you want to access classs, then you will have to create a managed
wrapper around your classes. Just setting the /clr switch is not going to
make your code accessible in .NET.

Hope this helps.

 

[Willy Denoyette [MVP]]

Hi all,

I have an existing Visual C++ project that builds a DLL (not COM or
ATL or anything). I wish to use this DLL in a Visual Studio 2005 C#
project without having to define each function and structure again in
the C# project (using pinvoke I believe).

I've done some reading around and it seems that what I'm after is
possible. I've added the old C++ project to my new C# solution and set
the compiler to use /clr. I can then add the DLL as a reference to the
C# project without any errors. However, I'm stuck there. How do I
actually invoke any of the methods in the DLL? Adding "using <DLL
name>" produces an error, and I'm not sure what else to try.

Thanks in advance,

Ben

You can't call methods on native classes from C#, compiling your C++ files with /clr don't
turn your native classes into managed classes.
All you can do is implement managed classes (wrapper or shim) using VC8, these classes can
create instances of the unmanaged classes and forward the calls to their unmanaged methods.

Willy.

 

[BDowling]

Ben,

The dll, does it export functions, or classes? If it uses functions and
structures, then you should not add a reference in your project to the dll.
You will have to make the calls to these functions through the P/Invoke
layer, which will require a re-declaration of the structures and the
functions in your code.

If you want to access classs, then you will have to create a managed
wrapper around your classes. Just setting the /clr switch is not going to
make your code accessible in .NET.

Hope this helps.

--
- Nicholas Paldino [.NET/C# MVP]
- (e-mail address removed)

Hi all,

I have an existing Visual C++ project that builds a DLL (not COM or
ATL or anything). I wish to use this DLL in a Visual Studio 2005 C#
project without having to define each function and structure again in
the C# project (using pinvoke I believe).

I've done some reading around and it seems that what I'm after is
possible. I've added the old C++ project to my new C# solution and set
the compiler to use /clr. I can then add the DLL as a reference to the
C# project without any errors. However, I'm stuck there. How do I
actually invoke any of the methods in the DLL? Adding "using <DLL
name>" produces an error, and I'm not sure what else to try.

Thanks in advance,

Ben

Hi Nicholas,

The DLL only has functions, no classes. I was hoping not to have to
use the P/Invoke layer, but is this the only option?

If so is there any automated way to generate the P/Invoke definitions
in the C# code? It is going to be a real pain otherwise, because I
have LOTS of functions.

Like I said, I have the Visual C++ project that produces the DLL, so
is there some way I could modify this project to make it easier to
integrate with my C# one? Ideally I'd like the the resulting DLL still
to be usable by non .NET projects.

Thanks, Ben

 

[Nicholas Paldino [.NET/C# MVP]]

Ben,

If the original project only exports functions, then you should not
modify the original project at all. The P/Invoke layer is exactly what you
need to use in order to make the calls in .NET.

Yes, it will be tedious to declare all the functions in .NET as well as
any structures you might use, but it is a one-time cost. Once you get it
right, it will just work from that point on.

There are no automated tools to do this either, AFAIK.

--
- Nicholas Paldino [.NET/C# MVP]
- (e-mail address removed)

Ben,

The dll, does it export functions, or classes? If it uses functions
and
structures, then you should not add a reference in your project to the
dll.
You will have to make the calls to these functions through the P/Invoke
layer, which will require a re-declaration of the structures and the
functions in your code.

If you want to access classs, then you will have to create a managed
wrapper around your classes. Just setting the /clr switch is not going
to
make your code accessible in .NET.

Hope this helps.

--
- Nicholas Paldino [.NET/C# MVP]
- (e-mail address removed)

Hi all,

I have an existing Visual C++ project that builds a DLL (not COM or
ATL or anything). I wish to use this DLL in a Visual Studio 2005 C#
project without having to define each function and structure again in
the C# project (using pinvoke I believe).

I've done some reading around and it seems that what I'm after is
possible. I've added the old C++ project to my new C# solution and set
the compiler to use /clr. I can then add the DLL as a reference to the
C# project without any errors. However, I'm stuck there. How do I
actually invoke any of the methods in the DLL? Adding "using <DLL
name>" produces an error, and I'm not sure what else to try.

Thanks in advance,

Ben

Hi Nicholas,

The DLL only has functions, no classes. I was hoping not to have to
use the P/Invoke layer, but is this the only option?

If so is there any automated way to generate the P/Invoke definitions
in the C# code? It is going to be a real pain otherwise, because I
have LOTS of functions.

Like I said, I have the Visual C++ project that produces the DLL, so
is there some way I could modify this project to make it easier to
integrate with my C# one? Ideally I'd like the the resulting DLL still
to be usable by non .NET projects.

Thanks, Ben

 

[BDowling]

OK thanks, sounds like P/Invoke is the way to go. However, I'm not
100% sure how to convert between the different types. For example, the
C++ functions take char *, and struts. Can I simply pass in a 'string'
as a char *? And do I need to redefine the strut in C#?

Thanks again, Ben

 

[Nicholas Paldino [.NET/C# MVP]]

Ben,

Check out the section of the MSDN documentation titled "Consuming
Unmanaged DLL Functions", located at:

http://msdn2.microsoft.com/en-us/library/26thfadc.aspx

This should give you the information that you need.

 

[BDowling]

OK I've decided that I don't want to go down the P/Invoke route, and
I'm not bothered about the DLL being used by other applications.
Basically I want the easiest method of integrating the functions with
my C# project. I could convert the C code to C# (although not easily).
Are there any other methods?

Thanks, Ben

 

[Peter Duniho]

OK I've decided that I don't want to go down the P/Invoke route, and
I'm not bothered about the DLL being used by other applications.
Basically I want the easiest method of integrating the functions with
my C# project. I could convert the C code to C# (although not easily).
Are there any other methods?

One method that I've found fairly easy, and simpler to get my poor little
head around, is to write a managed C++ wrapper for the unmanaged DLL. In
the managed C++ wrapper, you can create a managed class that your C# code
can call, and which calls the DLL in exactly the way that you'd normally
call a DLL from C++ code.

I wish the p/invoke stuff was better-documented, because it does include
(as near as I can tell) all of the necessary "glue" to import unmanaged
DLLs directly. But figuring out the exact magic incantation to get it to
work can be very frustrating sometimes. I think most programmers can
easily implement their own wrapper, converting between managed and
unmanaged data types explicitly. It's more tedious, but less mysterious.


Pete

 

[Guest]

Hi. Here you have an example on how you can use you C++ dll:

[DllImport("Kernel32.dll", CallingConvention = CallingConvention.StdCall)]
public static extern IntPtr LoadLibrary(string lpFileName);

Here "Kernel32.dll" should be replaced by the name of your dll and "...
IntPtr LoadLibrary(string lpFileName);" by your function in the dll.

This must be done within the class.

Bye.

 

[Ben Voigt]

Ben,

The dll, does it export functions, or classes? If it uses functions
and
structures, then you should not add a reference in your project to the
dll.
You will have to make the calls to these functions through the P/Invoke
layer, which will require a re-declaration of the structures and the
functions in your code.

If you want to access classs, then you will have to create a managed
wrapper around your classes. Just setting the /clr switch is not going
to
make your code accessible in .NET.

Hope this helps.

--
- Nicholas Paldino [.NET/C# MVP]
- (e-mail address removed)

Hi all,

I have an existing Visual C++ project that builds a DLL (not COM or
ATL or anything). I wish to use this DLL in a Visual Studio 2005 C#
project without having to define each function and structure again in
the C# project (using pinvoke I believe).

I've done some reading around and it seems that what I'm after is
possible. I've added the old C++ project to my new C# solution and set
the compiler to use /clr. I can then add the DLL as a reference to the
C# project without any errors. However, I'm stuck there. How do I
actually invoke any of the methods in the DLL? Adding "using <DLL
name>" produces an error, and I'm not sure what else to try.

Thanks in advance,

Ben

Hi Nicholas,

The DLL only has functions, no classes. I was hoping not to have to
use the P/Invoke layer, but is this the only option?

If so is there any automated way to generate the P/Invoke definitions
in the C# code? It is going to be a real pain otherwise, because I
have LOTS of functions.

Like I said, I have the Visual C++ project that produces the DLL, so
is there some way I could modify this project to make it easier to
integrate with my C# one? Ideally I'd like the the resulting DLL still
to be usable by non .NET projects.

You won't get that last wish, as what you're trying to do is to generate
MSIL metadata for all the functions. You can possibly get away with a
single source version to generate both native and .NET dlls, though.

Bracket your entire .cpp file with:

#if __cplusplus_cli
public ref struct ClassName abstract sealed {
#endif

....

#if __cplusplus_cli
};
#endif

 

[Ben Voigt]

Ben,

The dll, does it export functions, or classes? If it uses functions
and
structures, then you should not add a reference in your project to the
dll.
You will have to make the calls to these functions through the P/Invoke
layer, which will require a re-declaration of the structures and the
functions in your code.

If you want to access classs, then you will have to create a managed
wrapper around your classes. Just setting the /clr switch is not going
to
make your code accessible in .NET.

Hope this helps.

--
- Nicholas Paldino [.NET/C# MVP]
- (e-mail address removed)



Hi all,

I have an existing Visual C++ project that builds a DLL (not COM or
ATL or anything). I wish to use this DLL in a Visual Studio 2005 C#
project without having to define each function and structure again in
the C# project (using pinvoke I believe).

I've done some reading around and it seems that what I'm after is
possible. I've added the old C++ project to my new C# solution and set
the compiler to use /clr. I can then add the DLL as a reference to the
C# project without any errors. However, I'm stuck there. How do I
actually invoke any of the methods in the DLL? Adding "using <DLL
name>" produces an error, and I'm not sure what else to try.

Thanks in advance,

Ben

Hi Nicholas,

The DLL only has functions, no classes. I was hoping not to have to
use the P/Invoke layer, but is this the only option?

If so is there any automated way to generate the P/Invoke definitions
in the C# code? It is going to be a real pain otherwise, because I
have LOTS of functions.

Like I said, I have the Visual C++ project that produces the DLL, so
is there some way I could modify this project to make it easier to
integrate with my C# one? Ideally I'd like the the resulting DLL still
to be usable by non .NET projects.

You won't get that last wish, as what you're trying to do is to generate
MSIL metadata for all the functions. You can possibly get away with a
single source version to generate both native and .NET dlls, though.

Bracket your entire .cpp file with:

Just remembered you said you also had structures...

#if __cplusplus_cli
public ref struct ClassName abstract sealed {
#define REF public ref
#else
#define REF
#endif

.... changing every "struct" to "REF struct" as well ...


#if __cplusplus_cli
};
#endif