I've been provided a DLL that has been written in C++. Along with the DLL I receive the required input parms and expected output as well as a .h include file.
Can't seem to get it included as a Reference in my project. My procedure is to right click References and Add Reference, click Browse and then double click on the DLL. The error I get is:
A reference to 'c:......\dll' could not be added. Please make sure
that the file is accessible, and that it is a valid assembly or COM
component.
The problem is likely due to the name mangling of C++, but I'm not sure how to overcome the problem. I've been told by the author of the DLL that it was written for another customer who ran into the same issue, but was eventually successful in getting it referenced. I don't have access to that 'customer' and was wondering if anyone had suggestions.
Adding a reference is not how you link to this unmanaged DLL from your C# code. Instead you need to either:
Translate the header file to C# p/invoke calls, or
Create a C++/CLI wrapper around the unmanaged DLL and add a reference to that from your C# project. This option would typically involve linking to the .lib import library for the DLL which should be supplied with the DLL.
Related
I am trying to add a dll into my windows form application type project. However, when I am adding the dll to reference folder it is throwing an error and restricting me to add the same. Enclosed is a screenshot. Can anyone please let me know, under which condition we get this error and how to fix it?
Note: I am not aware, the dll has been produced using what tool or version/type of it.
screenshot of error
The message is:
A reference to C:\xyz.dll. dll could not be added, Please make sure
that the file is accessible and that it is a valid assembly or COM
component.
It's is exactly what you read and the message says.
Either thhis DLL doesn't contain any .NET code or class, or this DLL isn't a valid ActiveX DLL containing a typelib.
You can not add a DLL as a reference if it is not one of the above.
This is a possible duplicate to
Usually when we need to use native C++ DLL in C# program, write a manage wrapper is the way to achieve it.
Inside such program, If I press F12 (go to function definition) on a DLL function call, It goes to a C# file that looks like having all the functions forward declarations. I check the location of this file and it exist in the windows temp directory.
So my question is , When we uses a C++ unmanage DLL by manage wrapper in a C# program, Does .NET framework ( or any other component) create any temporary C# classes relevant to interface classes in the DLL?
There are no "temporary C# files". If you use Go to Definition and the IDE only has an assembly reference for the definition then it doesn't have a shot at finding the source code file for the definition. So it auto-generates one from the metadata in the reference assembly. That looks fairly similar to a source code file, but of course without any comments and without the code for the classes. It cannot be compiled. It is also in C#, even if the original assembly was created from C++/CLI or VB.NET code.
Nice feature, but don't confuse it for anything more than it is. If you want the IDE to take you to the actual source code file then you need a project reference, not an assembly reference, for the library.
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'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
Similar to coryr (see this question), I am referencing a dll within a C# project. The DLL often changes but I the C# project does not recognize this. Unlike coryr, the DLL is a VB6 ActiveX DLL. Any suggestions for how to reload the reference other than removing and adding it?
The problem here is that when you add a reference to a COM DLL, you don't actually add a reference to the DLL. Instead a primary interop assembly is generated for the DLL and a reference is added to that. When the main DLL is changed a new PIA (primary interop assembly) is not generated.
You can verify this by doing the following
Expand the references collection
Hit F4. This will bring up the properties page
Look at the path property
The path will be the path to the PIA.
The problem is that VS is watching the PIA and not the original DLL. So when the original DLL changes it doesn't actually reload the reference. The best way to get this to work is to unfortunately delete and re-add the reference.
Another solution is to manually generate the PIA and place it over the referenced PIA on disk. This will force VS to reload the DLL reference.