typedef struct
{
// The contents of this struct are platform-dependent and subject to
// change. You should not manipulate the contents of this struct directly.
/*New stuff*/
// HWND m_hWnd;
// HDEVNOTIFY m_hDevNotify;
} fdGlove;
FGLOVEAPI fdGlove *fdOpen(char *pPort, bool bOnlyAllowSingleConnection = false);
FGLOVEAPI int fdClose(fdGlove *pFG);
FGLOVEAPI int fdGetGloveHand(fdGlove *pFG);
FGLOVEAPI int fdGetGloveType(fdGlove *pFG);
I have a DLL file called fglove.dll and I need using C# to call it.
I have written code like this:
[StructLayout(LayoutKind.Sequential)]
public class fdGlove
{
}
[DllImport("fglove.dll")]
public static extern fdGlove fdOpen(string pPort, bool bOnlyAllowSingleConnection);
but when I debug the program it is has an error (Unable to find an entry point named 'fdOpen' in DLL 'fglove.dll'.)
Can someone point out what I have done wrong?
fdOpen is using a default parameter - which can only mean you are trying to export a C++ function out of a DLL. The result is that "fdOpen" is getting "name mangled" in the export table as something that looks like "fdOpen#YAXPB_W0I#Z".
You're better off exporting this function as C. Declare and define fdOpen as follows:
extern "C" fdGlove* __stdcall fdOpen(char* pPort, bool bOnlyAllowSingleConnection);
Other possible issues:
The DLL isn't in the same directory as the EXE trying to load it.
You forgot to export the function from the DLL. You need to use a .DEF file or the __declspec(dllexport) attribute on the function definition. Use "dumpbin /exports fglove.dll" to figure out if this is the case.
Confusion between stdcall and cdecl compile options. I get it confused, so try replacing "_stdcall" with "_cdecl" above. Or try it without either attribute.
The compiler of fglove is most likely doing so type of name mangling.
Use DUMPBIN fglove.dll to get the real names.
Then use [DllImport("fglove.dll", EntryPoint='...')] where ... is the real name.
look at the name of the exported symbol in Dependency Walker. More than likely it will be _fdImport or something similar and you will need to update your DLLImportAttribute to match the exported name.
Related
Given the following c++ class in foo.dll
class a{
private:
int _answer;
public:
a(int answer) { _answer = answer; }
__declspec(dllexport) int GetAnswer() { return _answer; }
}
I would like the pInvoke GetAnswer from C#. To do that, I use the following method:
[DllImport("foo.dll", CallingConvention = CallingConvention.ThisCall, EntryPoint= "something")]
public static extern int GetAnswer(IntPtr thisA);
And I pass in an IntPtr that points to an a (that I got from somewhere else, it's not important). CallingConvention = CallingConvention.ThisCall makes sure it's handled correctly
What's cool about this question is that I know I'm right so far because it's already working great! Using Depends.exe, I can see that "GetAnswer" is exported as ?GetAnswer#a##UAEHXZ (Or something close - the point being that it's been name mangled). When I plug the mangled name into the "something" for the EntryPoint everything works great! It took me about a day before it dawned on me to use Depends.exe, so I'm going to leave this here as a help to anybody who has a similar issue.
My REAL Question is: Is there any way to disable C++ name mangling on GetAnswer so that I don't need to put the mangled name in as my entry point. Having the mangled name in there seems like it could break, because my understanding of name mangling is that it can change if the compiler changes. Also it's a pain in the butt to use Depends.exe for every instance method that I want to pInvoke.
Edit: Forgot to add what I've tried:
I don't seem to be able to put extern "C" on the function declaration, although I can stick it on the definition. This doesn't seem to help though (which is obvious when you think about it)
The only other solution I can think of is a c-style function that wraps the instance method and takes an instance of an a as a parameter. Then, disable name mangling on that wrapper and pInvoke that. I'd rather stick with the solution that I already have, though. I already told my co-workers that pInvoke is great. I'm going to look like an idiot if I have to put special functions in our c++ library just to make pInvoke work.
You cannot disable mangling for a C++ class method, but you may well be able to export the function under a name of your choice using /EXPORT or a .def file.
However, your entire approach is brittle because you rely on an implementation detail, namely that this is passed as an implicit parameter. And what's more, exporting individual methods of a class is a recipe for pain.
The most sensible strategies for exposing a C++ class to .net languages are:
Create flat C wrapper functions and p/invoke those.
Create a C++/CLI mixed mode layer that publishes a managed class that wraps the native class.
Option 2 is preferable in my opinion.
You may be able to use the comment/linker #pragma to pass the /EXPORT switch to the linker which should allow you to rename the exported symbol:
#pragma comment(linker, "/EXPORT:GetAnswer=?GetAnswer#a##UAEHXZ")
Unfortunately, this does not resolve your need to look up the mangled name using depends or some other tool.
You do not have to disable the mangled name which actually contains lots of information of how the function itself is declared, it basically represents the whole signature of the function after the function name gets de-mangled. I understand you already found a word-around and the other answer has been marked as a correct answer. What I am writing below is how we can make it work as you desired.
[DllImport("foo.dll", CallingConvention = CallingConvention.ThisCall, EntryPoint = "#OrdinalNumber")]
public static extern int GetAnswer(IntPtr thisA);
If you replace "#OrdinalNumber" with the real ordinal number of GetAnsweer, such as "#1", it will work as you desired.
You may just consider the EntryPoint property is the same as the function name we pass to GetProcAddress where you can either pass the function name or the ordinal number of the function.
Your approach to calling non-static function members of a C++ class is indeed correct and thiscall is used correctly and that is exactly thiscall calling convention comes in play in C# P/Invoke. The issue with this approach is that you will have to look into the DLL's PE information, Export Function Information and find out the ordinal number for each function you would like to call, if you have a big number of C++ functions to call, you may want to automate such a process.
From the Question Author: The solution I actually went with
I ended up going with a c-style function that wraps the instance method and takes an instance of an a as a parameter. That way, if the class ever does get inherited from, the right virtual method will get called.
I deliberately chose not to go with C++/CLI because it's just one more project to manage. If I needed to use all of the methods on a class, I would consider it, but I really only need this one method that serializes the class data.
I have a weird problem I have C++ DLL that I am importing in C# library using DLL import. If I specify entry point, everything works as expected, here is the example:
internal static class UnsafeMethods
{
[DllImport("GoodSchool.dll", EntryPoint = #"?AddNum##YAHHH#Z")]
public static extern int AddNum(int num1, int num2);
}
class Program
{
static void Main(string[] args)
{
Console.WriteLine(UnsafeMethods.AddNum(4,5));
}
}
However, if I use a simplfied import like here:
[DllImport("GoodSchool.dll", CallingConvention = CallingConvention.Cdecl)]
public static extern int AddNum(int num1, int num2);
I get familiar error message:
Unhandled Exception: System.EntryPointNotFoundException: Unable to find an entry point named 'AddNum' in DLL 'GoodSchool.dll'
I used depends to verify that method is properly exposed, and I decoded notation to verify parameters and naming convention - all seems good.
Function signature in C++ is very simple:
__declspec(dllexport) int AddNum(int num1, int num2);
Any suggestions how I can call this method in C# without providing decorated name as EntryPoint? What do I do wrong? I do not want to use "C" export, as my understanding is that decorated function name is perfectly fine to be used with DllImport.
C++ mangles function names to account for function name overloading. After all, if the DLL had
__declspec(dllexport) int AddNum(int num1);
__declspec(dllexport) int AddNum(int num1, int num2);
which would AddNum refer to?
The symbol ?AddNum##YAHHH#Z is the mangled (a.k.a. decorated) name exposed in the unmanaged DLL.
https://en.wikipedia.org/wiki/Name_mangling#Name_mangling_in_C.2B.2B
Your DLL does not export something called AddNum.
The decorated function name is fine to use with DllImport, as you can see by the fact that you're doing it. But that requires you to specify the decorated function name in the import. The undecorated name does not exist as far as the linker (static or dynamic) is concerned -- AddNum is simply not a symbol that your library exposes.
If you instead want to do what you're asking:
call this method in C# without providing decorated name as EntryPoint?
then you cannot allow C++ to mangle the name in the first place. You can either specify the decorated name in DllImport or use extern "C" linkage on the C++ code. You must pick one or the other.
So I have this C .dll source code which I want to use in my C# application. Instead of doing bunch of DllImports I've decided to write a wrapper for it in C++/CLI.
My C function takes a pointer to a struct with 4 callback functions in it:
typedef struct
{
PFN_IN readFp;
PFN_OUT writeFp;
}OPEN_ARGS;
C++/CLI shares the same .h file, therefore uses the same typedef.
C# code has it's own definition of this structure and delegates for CBs, because I can't attach .h to C# project.
[UnmanagedFunctionPointer(CallingConvention.Cdecl)]
public delegate Int32 PFN_OUT(IntPtr arg, IntPtr pSrc, Int32 len);
[StructLayout(LayoutKind.Sequential)]
public struct OPEN_ARGS
{
public PFN_IN readFp;
public PFN_OUT writeFp;
};
So, when I add my C++/CLI dll explicitly to C# project references, the compliler wouldn't accept calls to C++/CLI functions saying
"Error 2 Argument 2: cannot convert from 'WrapperTest.Program.OPEN_ARGS' to 'SAR_OPEN_ARGS'"
But if I include the C++/CLI dll implicitly like that
[DllImport("Wrapper.dll", CharSet = CharSet.Auto, EntryPoint = "?CLIOpen##YAHHUOPEN_ARGS###Z")]
public static extern int CLIOpen(int a, OPEN_ARGS args);
It will work just fine.
So is there a way to tell C# compiler to ignore this type cast error, or may be other way to wrap C code functions?
EDIT: cleaned up variable names for better readabiltiy
What if you did this another way. Since you have a C++/CLI DLL handling interop duties between the C DLL and the C# assembly, you could expose an equivalent API, only using more .NET-like concepts.
For example, instead of exposing the struct with function pointers, you could expose a class that has three events. The C# assembly would add handlers for those events. Inside the C++ DLL, it would use the function pointers that the C DLL expects, but their implementation would fire the .NET events that the C# assembly is handling.
This would provide a much better experience using the DLL on the C# side, and likely get rid of the interop compiler errors that you're encountering.
Please consider using SWIG to generate the wrapper code for all your pinvoke.
http://www.swig.org/Doc1.3/CSharp.html
So for managed C++, you can use the #pragma managed/unmanaged compiler directives instead of pInvoke, which it looks like you are using. Then you can compile managed and native code together into the same assembly, even the same CPP file.
Then you could do something like:
#pragma managed
// include your native headers here
#include "foo.h" // whatever you call it.
#using <System.dll> // what ever else you need here...
// Have to wrap a function in a class, since .NET doesn't allow free standing functions.
public ref class foo
{
public static int sarCLIOpen(int a, SARWrapperTest::Program::SAR_OPEN_ARGS args)
{
// do something to convert your managed args to native args.
::SAR_OPEN_ARGS native_args = ...
// then call your native function
return sarCLIOpen(a, native_args );
}
};
I have following method in my Borland C++ code,
static bool UploadBitstream(void)
{
//Some code Implementation
}
And I'm trying to convert it to DLL and access it in C#.
What are the steps I need to follow to Convert the code DLL
and then use it in C# ??
First, you have to make sure that the methods are defined extern. Then you need to declare the method stdcall or pascal calling convention, and mark them dllexport. See code listing below (this is ancient memory for me, so pardon if I am a bit off on modern Borland C++ compilers).
// code.h
extern "C" {
#define FUNCTION __declspec(dllexport)
FUNCTION int __stdcall SomeFunction(int Value);
In the main
#include "code.h"
FUNCTION int __stdcall SomeFunction(int timesThree)
{
return timesThree * 3;
}
Once you've compiled your DLL all you should need to do in .NET to get access to it is use the DLLImport property.
public class stuff
{
[DLLImport("somedll.dll")]
public static extern void UploadBitstream();
}
If you need pointers or anything like that it gets more complicated but for void functions it's that simple.
It should be noted that once you invoke that function the dll will be loaded by your program and won't be released until your program is closed. You can dynamically load dlls but that is much more complicated. I can explain it here if you have a need.
Watch your terminology.
In your example UploadBitstream is function not a method.
If it is indeed a method in a class then it is very difficult to use classes from Borland compiled DLLs.
If your code is actually C not C++ you should be able to create a compatible DLL
for your simple C style functions with C++ Builder.
See the following SO question:
Use a dll from a c++ program. (borland c++ builder and in general)
where I list various compiler settings which will also apply to creating compatible DLLs.
In a function in my C++ DLL, I'm returning a std::string to my c# application. It pretty much looks like this:
std::string g_DllName = "MyDLL";
extern "C" THUNDER_API const char* __stdcall GetDLLName()
{
return g_DllName.c_str();
}
But when my C# code calls this function, I get this message in my output window:
Invalid Address specified to RtlFreeHeap( 00150000, 0012D8D8 )
The function declaration in c# looks like this:
[DllImport("MyDll", EntryPoint = "GetDLLName")]
[return: MarshalAs(UnmanagedType.LPStr)]
public static extern string GetDLLName();
From what I've been able to find online, sometimes this message appears when there's an inconsistency between which version of new(debug or release, etc) is being used with delete. But I'm not sure if that is what is going on in my case. So I'm not sure exactly what's causing it. Maybe the MashallAs might have something to do with it?
Any ideas?
Thanks!
I managed to find the issue. It was the way the C# definition was done. From what I can understand, using the MarshallAs(UnmanagedType.LPStr) in combination with the string return type makes it so that it'll attempt to free the string when its done. But because the string comes from the C++ DLL, and most likely a totally different memory manager, it fails. And even if it didn't fail, I don't want it to be freed anyway.
The solution I found was to change the C# declaration to this (the C++ code is unchanged):
[DllImport("MyDll", EntryPoint = "GetDLLName")]
public static extern IntPtr GetDLLName();
So this makes it so that it just returns a pointer to the string data. And then to change it to a string, pass it to Marshal.PtrToStringAnsi()
return Marshal.PtrToStringAnsi(GetDLLName());
And that gets wrapped into another function for cleanliness.
I found the solution from this page:
http://discuss.fogcreek.com/dotnetquestions/default.asp?cmd=show&ixPost=1108