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
Related
I have a c++ project compiled with /clr support(e.g. wrapper.dll). This project(wrapper.dll) is a wrapper between .Net enviroment and unmaged dll(e.g. noCode.dll), which inherits from. I dont have access to code of inherited dll(noCode.dll), but I can link it to my wraper (by noCode.lib and noCode.h files).
When I want to use my wraper(wrapper.dll) in c# project I reference it and have to copy my unmanaged dll(noCode.dll) to location of c# project execution.
Is it possible to merge c++ unmamaged dll(noCode.dll) to managed dll(wrapper.dll) to allow to use only one file by reference(noCodeWrapper.dll) in c# projects?
It is not possible to link DLL files together.
But you can add that nocode.LIB to your DLL and then you don't need [DllImport]. Since you have LIB and H files, you can call the "nocode" functions directly from your managed C++ code.
If you had access to noCode.dll source code you could integrate it with wrapper.dll. Otherwise merging DLL binaries is not a task that could give predictable results.
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.
My project structure is as follow:
ASP.NET calling C# layer calling Managed C++ calling Native C++
(i'm trying to avoid using interop so this is why the managed c++ layer)
I wrote unit test that test the C# layer and it works fine.
When I try to run the asp.net page i'm getting: "Could not load file or assembly..." error.
I figured out that when i copy paste the Native C++ dll to "Temporary ASP.NET Files" (to the corresponding folder) the site works.
It seems that the Managed C++ code can find the Native C++ code only if it resides in the same folder - obviously I can't have my Native dll in the temp files.
Is there a way to set the Native in a global place(doesn't work with System32)?
Thanks for you comments.
It boils down to one option:
It is security issue
i set up the server it self with the code and it runs under the cassini, but when i publish it(to run under iis7) i'm getting "Could not load file or assembly ...."
i'm running IIS7 with ApplicationPoolIdentity , .net 4 Integrated
Thanks a lot,
Pini.
Well technically using Managed C++ in this way is a form of Interop between native / managed code, the commonly used alternatives being COM and P/Invoke. This is purely a terminology thing however, you would get the same issue using P/Invoke.
This blog article Loading C++ Assemblies in ASP.Net might help you out - In short you need to either:
Set the %PATH% environment variable before the Managed C++ assembly attempts to load your native C++ dll.
Use the DllImport attribute to set the dll path (not applicable in your case as you aren't using P/Invoke)
Manually load the C++ dll yourself (e.g. with LoadLibrary) before the Managed C++ assembly attempts to load your native C++ dll.
I suspect that installing your dll to Win SxS would also work, but I don't know enough about how this works to be sure.
You can set your path variable?
You set it by going to the Properties of "My computer"/"Computer (Windows-PauseBreak) and then clicking advanced settings. Click advanced. Environment variables. Modify "Path" under system variables as needed.
I had to flip a bool in the ApplicationPoolIdentity. One of the filed in the properties says "enable 32bit" and that did the trick :) the default is False
My server is 64bit and i build my native with 32bit.
I've been given a dll to talk to a device, I have little to no experience in C# and I'm supposed to get the device initialized by the end of the week. The dll has methods to open ports and send messages, but I have no idea how to get access to the functions
I know its a bit ridiculous to ask but im running out of time.
Thanks,
Add a Reference to the .dll file in your C# project.
Add a Using namespace at the top of whatever class is going to interact with the .dll methods.
You will now be able to access the methods.
Edit: If your library is unmanaged you'll have to use Pinvoke.
Generally speaking, a feature to call from managed code into unmanaged code (which I assume your DLL is) is called P/Invoke and generally involves annotating required static extern methods with attributes.
Add a reference to the dll in your project (selet browse to find it) and you should be able to access the functions within. As for how to make your device work with it, I think you're on your own :)
If the DLL is a .Net assembly, you can load it into a Visual Studio project by adding it as a reference.
In the absence of documentation, it can also be extremely helpful to load the assembly into .Net Reflector, which lets you inspect the guts of the assembly, even to the point of disassembling the code inside the methods.
1- If it is managed Dll , i.e. Written using .net framework than calling a method from the dll is like you are calling a method from your own class.
just add the reference of the dll in your project and include the namespace reference by 'Using' keyword.
2- If it is not than you need to import your dll dynamically, you can use [DllImport]
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.