I am trying to run un-managed native C++ class code from C# by writing a wrapper. My C++ code compiles as a static library (.lib) with no problems. The code depends on other code which, I believe, are all compiled as static libraries. I am not able to compile this as a DLL as there are linker errors.
I have just learnt that the wrapper needs to be compiled as a DLL so that it may be invoked from C#. Is this true? Can I not compile my wrapper as a static library to be used in C#?
C# cannot load .lib files.
P/Invoke can only load .DLL files (they don't have to be named .DLL but they have to be the right file format).
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.
I want to create a dll in visual c#, and use it in win32 program (visual c++).
From what I understand, for adding dll file in Visual C++ , I need also .h file and .lib file, but when I create a class library in visual c# I only get dll file.
Is it possible to create a .h file and .lib file in visual c# ?
No, it's not possible. But here is what you can do to use a C# library in C++:
C++/CLI Wrapper (this allows you to have both managed and unmanaged code in the same source file. The managed portion can then call the C# code). Here you can find an example.
Host CLR (the CLR acts as a library that can be loaded and "hosted" by a process).
COM Interop (expose your .NET type as a COM interface and matching coclass which you can easily use from unmanaged C++).
This thread is also quite interesting!
You could use LoadLibrary and GetProcAddress to load the DLL dynamically and you wouldn't need to create the files you refer to. You can read more here.
Using VS2010, I am working on wrapping a large number of .h files and one .lib from native C++ (using MFC) to C++/CLI for eventual use as a referenced .dll in C#.
While creating the wrapper I'm getting compiler errors stating CObject is undefined. In the project properties I have set use of MFC to use MFC in a static library and runtime library to multi-threaded debug DLL (/MDd). I am linking the .lib and including the .h files. The compiler errors are in the .h files where some of the classes are inheriting from CObject.
Shouldn't the compiler know about CObject?
Are you #including the MFC headers? afx.h, afxwin.h, anything like that? It's possible that #include was in stdafx.h in your native C++ project, and didn't get copied into the header files that you're using in your C++/CLI project.
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.