I am wrote a visual c++ win32 console app, and i wrote it and tested it in
win32 console project
. then i switch to
win32 project
and imported all the source files and created a dll for it. by mark the class i want to export as
#define DllExport __declspec( dllexport )
class DllExport theClass {
}
it works and the dll is generated. then i created a another c# project and want to add the dll to the project. by reference->add reference-> browser. then i select that dll.
then it is gives me an error
a reference to the '''''''.dll could
not be added. please make sure that
the file is accessible, and that is a
valid assembly or com component.
anyone knows where i did wrong to generate/import the dll?
thanks
The Add Reference dialog can only work for DLLs that contain metadata (managed code) or a type library (a COM server). Your DLL doesn't fit that bill, you can only use the [DllImport] attribute in C# code to use the P/Invoke marshaller to call an unmanaged DLL entrypoint.
That can not be a native C++ class, like you are trying to do, there is no reliable mechanism for managed code to allocate unmanaged memory and call the constructor (and destructor) of a native C++ class. Short from the difficulty of finding the constructor and destructor code, there is no way for the P/Invoke marshaller to know the size of the object. The C++ language doesn't generate the metadata necessary to know this required information.
If you want to pursue P/Invoke then write an plain global function, decorated with extern "C", __declspec(dllexport) and (optionally) __stdcall.
If you want to export a C++ class then the only avenue is using the C++/CLI language and write a "ref class" wrapper for the native C++ class.
Or you could write a COM coclass, the universal glue in Windows. Very well supported by .NET, probably not something you want to pursue if you never wrote COM code before. ATL is the best way to get one going.
Related
I have a c dll, which is an api which exposes many methods. I want to replace this dll with one written in a more up to date language. However, I have customers who have integrated to the c dll already, and I want to just give them the new c# dll which replicates the c dll. I need to do this in such a way as the customers who have integrated to the c dll are not affected at all. i.e. I just want to replace the c dll with the c# one, and it should seem seamless to them.
Is this technically feasible? And if so, how should I go about replicating the c interface in c#.
I have a number of methods in the c dll is defined with dllexport
__declspec( dllexport ) void __stdcall
You can't do that with a C# dll. You would have to write a COM wrapper for the managed dll, and client code would then have to link against the COM wrapper's type library (*.tlb).
You could do that with C++/CLI, by building a mixed-mode dll that exposes the native interface to unmanaged code. Then you would just distribute the dll and the .lib file like normal, and client code would just link against the .lib file (as it presumably does now).
That's a fair bit of work, though. Unless there is some problem with the original C dll, I don't think I would go to the trouble.
We're creating a dll, written in C++, providing access to some hardware. We also have a C# program that uses this dll.
We're having an issue with the versions. Indeed, when running the C# program, it absolutely wants to use the exact C++ dll version it used when compiling. I.e. if the C# program was compiled using C++ dll 1.2.3.4, then the program will refuse to run with C++ dll 1.2.3.5.
I'd like to instruct the C# program to use any C++ dll with version 1.2.anything.
Where can I configure this in the C# project?
This question has been superseded by that one, more related to COM.
Nothing this fancy exists in C++. Using a side-by-side manifest technically permits this but you would have known about it since you would have typed the version number in the manifest of your C# program.
The far more likely explanation is that you actually created a C++/CLI assembly. Many programmers confuse C++/CLI with C++. Easy mistake since that language permits using native C++ code. But it actually gets compiled to a mixed-mode assembly, an assembly that contains both IL and native code. The normal CLR version checking occurs for such an assembly when the CLR loads it, it is only happy with an exact version match. A strong DLL Hell counter-measure.
And the normal CLR version wrangling option is available to bypass this check, a <bindingRedirect> element in your app.exe.config file. As well as controlling the assembly version number the way you do it for your C# code so this isn't necessary.
The easiest way to check if this guess is accurate is by using Project + Add Reference and select the DLL. If that doesn't draw any complaint and the assembly gets added to the References node of your C# project then you know it is a normal .NET assembly. Don't forget to take advantage of that, no pinvoke required.
Load the dll at runtime and use reflection to call it's methods.
Assembly assembly = Assembly.LoadFrom("C:\\test.dll");
Assembly.GetTypes();
Activator.CreateInstance(type);
I don't think it is possible to configure your program to use 1.2.* version and no others. Unless you would write the code for that on your own. Another possibility would be not to change the version tag of the C++ dll, but it does not seem you want to that.
A solution avoiding the version dependency would be the usage of dllimport. You can load any dll written in C++ with it. It is free of version dependency. See the example from the msdn and link at the end:
using System;
using System.Runtime.InteropServices;
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);
}
}
Description in MSDN
I have several Unmanaged C++ written lib files which I need to link to Managed C++ dll.
Then I need to invoke functions of this Managed C++ from C# application.
First step is OK - Managed C++ dll is created, I can see with ildasm that it exports functions I need. However when I try to call this function from my C#-written test app it says:
An unhandled exception of type 'System.IO.FileLoadException' occurred in Unknown Module.
A procedure imported by {MyManagedCPP.dll} could not be loaded.
This message goes from VS2010.
I made simple experiment - removed dependencies from all lib files in Managed C++ dll and rebuild it.
With this change it is OK - app starts, I can call functions of Managed C++ dll from C# test app.
Is it not possible by design to call managed c++ functions when dll has static linkage with lib files? Technical restriction? Or there is some workaround?
Thanks
You no doubt have an implicit dependency on a native DLL. It isn't clear from the question what DLL that might be. It could be msvcrxx.dll for example, a runtime support library for native C++ code. Which would be rather bad, you don't want to mix CRT versions. Such a missing DLL otherwise prevents the C++/CLI assembly from getting loaded, producing the FileLoadException.
If you have no idea what that DLL might be then you could use SysInternals' ProcMon utility. The trace will show you the program searching for the DLL and not finding it. If it is msvcrxx.dll then be sure to rebuild the .lib files using the same compiler version you used to build the C++/CLI assembly. If it is something else then make sure you copy that DLL to the build directory.
I have windows form application written in VC ++ . I want to change the button click in this app (WInform app in VC++) to hit a function written in C#.
What are the possible ways to do this.
Calling a C# assembly without compiling with C++/CLI is tricky. some of the ideas I've had:
a) Create a mixed-assembly wrapper dll (mixed assemblies contain both native code and managed code). Add a reference to your C# assembly, then create functions in your dll that call the C# code via C++/CLI, then define dll entrypoints ( __declspec(dllexport) ) for those functions. You can now link against the dll as it will provide a native interface that C++ can understand, while internally that dll can call your C# code.
( Afterthought: You can probably compile this to a .lib, that would be easier than a dll.)
Walkthrough: Creating and Using a Static Library
b) Use Mono to call the C# assembly. Mono has a C API which you can use to load and use managed assemblies without using c++/CLI. This is what I would do if C++/CLI is not an option.
Embedding Mono
c) If your function has a relatively simple input/output signature (no large objects, etc) you might consider compiling your C# function into an executable and use standard input/output to call the function. You'll have to carry input arguments and the output as text, though. Then make C++ start the executable and pass some input to it, and read the output.
I'm trying to use the lame_enc.dll file from LAME in a C# project, but adding the thing seems impossible.
I keep getting an error that says that a reference could not be added and to please check if the is accessible, a valid assembly or COM component.
I have no C++ experience, though I would like to use the functionality. Right now I'm using Process from the .NET framework to call lame.exe and do stuff, but I'd like to know if there's another way.
You can only add managed assemblies as a reference to a managed project. What I normally do in this situation is to add it as ressource instead with "copy local" settings. That way the DLL is tied to and deployed with your project. I then use DllImport to manually get the APIs I need from that DLL.
You have to use P/Invoke to call unmanaged APIs from managed code.
To use an unmanaged dll (native C++) in C#, you have to use DllImport, not adding a reference to the project in visual studio (and that is why you get an error).
Here is the documentation of DllImport from the MSDN.
You will need to use PInvoke to call functions in your native lame dll. However, you will only be able to call functions that have been exported as "C" style.
You can use a tool like "PInvoke Interop Assistant" that will help you when working out the PInvoke call signatures to make calls from C# to your native dll:
http://clrinterop.codeplex.com/releases/view/14120