I'm trying to make a non-static vendor C++ DLL accessible via C#. In order to do this, I'm writing a managed C++ wrapper DLL which basically creates static variables for the vendor DLL and makes those accessible to the C# application.
Here's an example:
typedef void(__stdcall *LPLISTENER_FUNC)(VENDORHANDLE hModule, VENDORWPARAM wParam, VENDORLPARAM lParam);
public delegate void VENDOR_Delegate(VENDORHANDLE hModule,
VENDORWPARAM wParam, VENDORLPARAM lParam);
public class VENDORWrapper
{
private:
static VENDORHSTORAGE _hStorage;
static VENDOR_Delegate^ _hOpenCallback;
void static Initialize()
{
_hStorage=storage_initialize();
}
void static registerCallback(unsigned int type, VENDOR_Delegate^ callback)
{
if (type == 2)
{
_hOpenCallback = callback;
::storage_register_callback(_hStorage, type, (LPLISTENER_FUNC)&_hOpenCallback);
}
}
bool static Open(String^ file)
{
bool retval=false;
filePath = file;
IntPtr ip = Marshal::StringToHGlobalAuto(filePath);
LPCWSTR str = static_cast<LPCWSTR>(ip.ToPointer());
//ERROR OCCURS HERE
retval = storage_open(_hStorage, str);
Marshal::FreeHGlobal( ip );
return retval;
}
void static Close()
{
storage_close(_hStorage);
}
}
The C# is skeletal:
public static VENDORStorageWrapper.VENDOR_Delegate openCallback
= new VENDORStorageWrapper.VENDOR_Delegate(fileOpened);
static void Main(string[] args)
{
VENDORStorageWrapper.VENDORStorageWrapper.Initialize();
Debug.WriteLine("DLL initalized");
VENDORStorageWrapper.VENDORStorageWrapper.registerCallback(2,
openCallback);
Debug.WriteLine("Callback registered");
VENDORStorageWrapper.VENDORStorageWrapper.Open("blah_file");
Debug.WriteLine("File opened");
}
public static void fileOpened(System.Int32 hstorage, System.UInt32 wParam, System.Int32 lParam)
{
Debug.WriteLine("file opened");
}
The vendor DLL's functions are specified as __stdcall, so I think I'm compliant on that front. The vendor's initialize call (_storage_initialize above) seems to be properly setting the handle, which is statically scoped. The storage_open call that's leading into the exception accepts a VENDORHANDLE (really a long) and an LPCWSTR, which I'm trying to convert the string passed from C# to. I think that's where the problem is...
When run, the app throws an unhandled exception "System.Runtime.InteropServices.SEHException" at the commented line above. The exception's coming from inside the vendor DLL, which I have no source code for. The vendor library works perfectly when called in an unmanaged C++ context and the file is known to be good. I think I'm missing something obvious in how I'm handling the parameters, but I can't see what it is.
I also don't think I have the callback set up properly, but I'm not the point where I can test that yet. Any ideas?
I'm not sure of the true big picture, but my experience using native DLLs with .net c# or vb, create a simple c# wrapper (just declarations) to the native DLL, instead of a c++ wrapper. Maybe this will help if the vendor DLL is really a vanilla DLL, as most are, like Windows api calls.
namespace MyNameSpace
{
public class MyWrapper
{
// passing an int to the native DLL
[DllImport("Vendor.DLL")]
public static extern int DllFunc1(int hModule, int nData);
// passing a string to a native DLL expecting null terminated raw wide characters //
[DllImport("Vendor.DLL", CharSet=CharSet.Unicode )]
public static extern int Dllszset(int hModule, string text);
}
}
Then .net will handle it for you and you call your vendor function as...
MyNameSpace.MyWrapper.Dllszset(h, "hello");
Hope this helps you or someone.
Related
I'm having trouble converting a C++ .dll function to C#.
The function is this:
void funct(void*(*handler)(void*));
I think this means passing a pointer to function taking a void pointer and returning a void pointer, as explained here:
Passing Function Pointer.
What I'm trying to do is do the same thing in C#, but I have do idea how. I tried to use delegates, but I am both unsure how to and also if they can even do what I am trying to do.
Thanks for the help!
EDIT:
Here are the C++ functions for register_message_handler and message_handler:
void register_message_handler(void*(*handler)(void*));
void *message_handler(void *raw_message);
EDIT:
xanatos has the exact explanation and conversion to C# below. Thanks a ton xanatos!
void funct(void*(*handler)(void*));
is a function that accepts a pointer and returns a pointer.
In C# it would be:
IntPtr MyFunc(IntPtr ptr);
So you'll need a delegate like:
public IntPtr delegate MessageHandlerDelegate(IntPtr ptr);
[DllImport("mydll.dll")]
public static extern void register_message_handler(MessageHandlerDelegate del);
Note that P/Invoke (calling native methods) is one of the rare cases where Action<...> and Func<...> delegates don't work, and you have to build "specific" delegate.
BUT to call it, it's a little complex, because you must save a "copy" of the delegate so that if the C functions calls this method at any time, this copy is still "alive" and hasn't been GC (see for example https://stackoverflow.com/a/5465074/613130). The most common way to do it is to encapsulate everything in a class, and put the copy in a property/field of the class:
class MyClass
{
public delegate IntPtr MessageHandlerDelegate(IntPtr ptr);
[DllImport("mydll.dll")]
public static extern void register_message_handler(MessageHandlerDelegate del);
[DllImport("mydll.dll")]
public static extern IntPtr message_handler(IntPtr message);
public MessageHandlerDelegate Del { get; set; }
public void Register()
{
// Make a copy of the delegate
Del = Handler;
register_message_handler(Del);
}
public IntPtr Handler(IntPtr ptr)
{
// I don't know what ptr is
Console.WriteLine("Handled");
return IntPtr.Zero; // Return something sensible
}
}
Note that if you use IntPtr then you don't need the unsafe.
If you want to pass message_handler to register_message_handler the safest way is to
// Make a copy of the delegate
Del = message_handler;
register_message_handler(Del);
There is a possibility that you can do directly no there isn't, checked
register_message_handler(message_handler);
and that the CLR will solve this, BUT I'm not sure of this... I can't easily test it, and I wouldn't do it. (if you want to test it, add a GC.Collect() just after the register_message_handler. If after some time you receive a CallbackOnCollectedDelegate error then you know you can't do it :-) )
Mmmh... checked. You can't do the raw register_message_handler(message_handler), you have to use MyClass.
Be very aware of something: it's better to always specify the calling convention C-side and C#-side even in function pointers. C# uses stdcall, while C uses cdecl. In x86 mode you can get very awful silent crashes (in x64 there is a single calling convention)
void __stdcall register_message_handler(void* (__stdcall *handler)(void*));
void * __stdcall message_handler(void *raw_message);
and C# side
[UnmanagedFunctionPointer(CallingConvention.StdCall)]
public delegate IntPtr MessageHandlerDelegate(IntPtr ptr);
[DllImport("Win32Project1.dll", CallingConvention = CallingConvention.StdCall)]
public static extern void register_message_handler(MessageHandlerDelegate del);
[DllImport("Win32Project1.dll", CallingConvention = CallingConvention.StdCall)]
public static extern IntPtr message_handler(IntPtr message);
(or everywhere cdecl)
I'm using Visual Studio 2010 and coding in c#.
public partial class App : Application
{
[DllImport("ewfapi.dll")]
public static extern IntPtr EwfMgrOpenProtected(string lpVolume);
[DllImport("ewfapi.dll")]
public static extern bool EwfMgrCommit(IntPtr hDevice);
public static bool EWFcommit()
{
temp = true;
string strVolumeName = "C:";
hProVol = EwfMgrOpenProtected(strVolumeName);
temp = EwfMgrCommit(hProVol);
return temp;
}
}
The problem I'm having is that these commands do not work on the machine with the EWF enabled.
I've attempted to get the Volume Name from ewfmanager instead of hardcoding it to "C:". However, I'm still learning and I'm having trouble using the command "EwfMgrGetProtectedVolumeList". This api command will return the VolumeName I need to run the other ewfapi commands. However, this command returns "PEWF_VOLUME_NAME_ENTRY " variable which I need to define. This is where I get stuck.
In C++, the header file defines this variable, but in c# header files are non existent. Would I have to convert C++ code to c# code in order to use structures defined in the header file?
Currently, I'm using a work around by executing the commands via command prompt which works flawlessly. But, I'm curious and want to learn the "right"/best way to do this in c#.
Please let me know of any experience using api commands in C#. Thank you.
This is the code I'm trying to convert to C#. I'm unsure how to convert the Declarators in C++ to C#.
typedef struct _EWF_VOLUME_NAME_ENTRY
{
struct _EWF_VOLUME_NAME_ENTRY* Next;
WCHAR Name[1];
} EWF_VOLUME_NAME_ENTRY, * PEWF_VOLUME_NAME_ENTRY;
This is the converted C# code without the declarators:
public struct EWF_VOLUME_NAME_ENTRY
{
/// _EWF_VOLUME_NAME_ENTRY*
public System.IntPtr Next;
/// WCHAR[1]
public string Name;
}
Your attempt was actually really close, it just needed some attributes to help the compiler along (in fact it may have worked without them)
[StructLayout(LayoutKind.Sequential)]
public struct EWF_VOLUME_NAME_ENTRY
{
/// _EWF_VOLUME_NAME_ENTRY*
public System.IntPtr Next;
/// WCHAR[1]
[MarshalAs(UnmanagedType.ByValTStr, SizeConst=1)]
public string Name;
}
To use it, the P/Invoke signature of your method would be.
[DllImport("ewfapi.dll")]
public static extern IntPtr EwfMgrGetProtectedVolumeList();
You also need a few more functions
[DllImport("ewfapi.dll")]
public static extern void EwfMgrVolumeNameListDelete(IntPtr list);
[DllImport("ewfapi.dll")]
public static extern bool EwfMgrVolumeNameListIsEmpty(IntPtr list);
[DllImport("ewfapi.dll")]
public static extern void EwfMgrVolumeNameEntryPop(ref IntPtr list);
You could then get the list of protected volumes like so.
public IEnumerable<string> GetProtectedVolumeNames()
{
var listptr = EwfMgrGetProtectedVolumeList();
if(listptr == IntPtr.Zero)
throw new Win32Exception(); //the default constuctor calls Marshal.GetLastWin32Error() for you.
try
{
while(!EwfMgrVolumeNameListIsEmpty(listPtr))
{
var currentStruct = Marshal.PtrToStructure<EWF_VOLUME_NAME_ENTRY>(listPtr);
// Pre .NET 4.5.1 version
// var currentStruct = (EWF_VOLUME_NAME_ENTRY)Marshal.PtrToStructure(listPtr, typeof(EWF_VOLUME_NAME_ENTRY));
yield return currentStruct.Name;
EwfMgrVolumeNameEntryPop(ref listPtr);
}
}
finally
{
if(listptr != IntPtr.Zero)
EwfMgrVolumeNameListDelete(listptr);
}
}
Note this code was written in the browser and is untested, but I think it should work.
EDIT: Important note, if you use this function outside of a foreach and instead manually go through the IEnumerable be sure to dispose of it, otherwise the finally block will not execute and you will have a memory leak (a foreach automatically calls dispose for you when you leave the scope of the loop).
On a side note you may want to check out this old MSDN Magazine article: "Making PInvoke Easy". It includes a link to a program that you can give it the C/C++ signature and it will give you back a rough version of the .NET P/Invoke signature.
Minor tweak to Scotts answer. The name is a null terminated string, so increase the SizeConst to get the rest of the characters of the name:
[StructLayout(LayoutKind.Sequential)]
public struct EWF_VOLUME_NAME_ENTRY
{
/// _EWF_VOLUME_NAME_ENTRY*
public System.IntPtr Next;
/// WCHAR[1]
[MarshalAs(UnmanagedType.ByValTStr, SizeConst=300)]
public string Name;
}
I want to link an unmanaged C++ library to a C# app. I am using the PInvoke process because the unmanaged C++ dll has multiple dependencies that won't compile with CLR. When I compile the example code below, I am getting the following errors. I did find a reference that I need to add the dll reference, but MSVS tells me it can't add it. I also read about registering it with the regsvr32, but that appears to be specific to CLR libraries, right? So my question is, how do I get clear this error for a unmanaged dll?
ServerTerminal.cs(62,48): error CS1031: Type expected
ServerTerminal.cs(62,48): error CS1519: Invalid token ';' in class, struct, or interface member declaration
ServerTerminal.cs(64,48): error CS1031: Type expected
ServerTerminal.cs(64,48): error CS1519: Invalid token ';' in class, struct, or interface member declaration
ServerTerminal.cs:
class ServerTerminal
{
private delegate int Callback(string text);
private Callback mInstance;
public ServerTerminal()
{
mInstance = new Callback(Handler);
SetCallback(mInstance);
}
public void Test()
{
TestCallback();
}
private int Handler(string text)
{
return 0;
}
[DllImport(#"..\\lib\\DDS_Service.dll", EntryPoint="SetCallback")];
private static extern void SetCallback(Callback fn);
[DllImport(#"..\\lib\\DDS_Service.dll", EntryPoint="TestCallback")];
private static extern void TestCallback();
}
and the C++ DLL's Component.h:
typedef int (__stdcall * Callback)(const char* text);
Callback Handler=0;
class COM_Component : public CM_Component
{
// Contents not pasted
}
and the C++ DLL's Component.cpp:
extern "C" __declspec(dllexport)
void __stdcall SetCallback(Callback handler)
{
Handler = handler;
}
extern "C" __declspec(dllexport)
void __stdcall TestCallback()
{
int retval = Handler("hello world");
}
COM_Component::COM_Component( void ) : CM_Component( TDstring( "COM_Component" ) )
{
// register the observer callback methods
}
// Remainder of file not pasted
Your "invalid token" compiler errors are due to the semicolon immediately after the DllImport attributes. Additionally, you're specifiying a verbatim #"..." string with double backslashes in it. I think your declaration should look like:
[DllImport(#"..\lib\DDS_Service.dll", EntryPoint="SetCallback")]
private static extern void SetCallback(Callback fn);
If your DLL is a COM dll, then you can run regsvr32 to register it, and add a reference to it in your project. If that's the case, then you don't need to use P/Invoke: you would be able to reference it like any other library.
[DllImport(#"..\\lib\\DDS_Service.dll", EntryPoint="SetCallback")];
private static extern void SetCallback(Callback fn);
[DllImport(#"..\\lib\\DDS_Service.dll", EntryPoint="TestCallback")];
private static extern void TestCallback();
Remove the ; in the lines after the DllImport attribute.
I have some C code which will be called from C# using P/Invoke. I am trying to define an C# equivalent for this C function.
SomeData* DoSomething();
struct SomeData
{
...
}
How do I import this C method to C#? I am having trouble defining the return type of the function.
EDIT:
i had a bunch of functions to import. This is one which had me stuck.
[DllImport("SomeDll.dll")]
public static extern IntPtr DoSomething();
I thought about using IntPtr, even if its the right way what after that?
I'm not quite sure I understand your question but I'll give a shot at answering it. You need to define the structure that is being returned from your C function and use Marshal.PtrToStructure to use the returned structure.
[DllImport("SomeDll.dll")]
public static extern IntPtr DoSomething();
public struct SomeData
{
//...
}
//code to use returned structure
IntPtr result = DoSomething();
SomeData structResult = (SomeData)Marshal.PtrToStructure(result, typeof(SomeData));
I am guessing that what you are trying to achieve is the following:
Your C/C++ native method takes no parameters and returns a pointer to a structure.
The C# equivalent is to return an IntPtr (pointer).
The problem is that you cannot resolve the IntPtr to the structure in C#
...research this:
Marshal.PtrToStructure(IntPtr, Type)
http://msdn.microsoft.com/en-us/library/4ca6d5z7.aspx
You can wrap your code up like so
public static class UnsafeNativeMethods
{
[DllImport("SomeDll.dll")]
private static extern IntPtr DoSomething(); //NO DIRECT CALLS TO NATIVE METHODS!!
public static SomeData SafeDoSomething()
{
try
{
return (SomeData)Marshal.PtrToStructure(DoSomething(), typeof(SomeData));
}
catch(Exception ex)
{
//handle exception
}
}
}
I have an C++ DLL in which the following functions are exported.
double getDouble(std::wstring filename, std::string ID, status &stCode);
int getInt(std::wstring filename, std::string ID, status &stCode);
float getFloat(std::wstring filename, std::string ID, status &stCode);
string getString(std::wstring filename, std::string ID, status &stCode);
int* getIntArray(std::wstring filename, std::string ID, status &stCode);
float* getFloatArray(std::wstring filename, std::string ID, status &stCode);
string* getStringArray(std::wstring filename, std::string ID, status &stCode);
where status is of enum type...
Now I want to use this DLL in my C#.NET app... Can anyone tell me how do i delclare the respected methods in C# and can make a call to this methods.... Thanks in advance...
[DllImport("external.dll", SetLastError = true, CallingConvention = CallingConvention.Cdecl)]
public static extern MbStatus queue_accept(
int reader,
[MarshalAs(UnmanagedType.LPStr)] string status);
Lookup the parameters for the DllImport attribute. Depending on your DLL those might need to be adjusted!
Side note: I usually wrap the external dll in an interface and a code layer to decouple it for tests and load it with dependency injection. I also don't change the naming conventions.
public interface IExternalDllInterop
{
MB_STATUS queue_accept(int reader, string status);
}
public class AmbInterop : IAmbInterop
{
public MbStatus queue_accept(int reader, string status)
{
return StaticAmbInterop.mb_queue_accept(reader, message, status);
}
}
Yes. You can. Actually, not std::string, std::wstring, any standard C++ class or your own classes can be marshaled or instantiated and called from C#/.NET. You will need to write a wrapper class for each of the C++ class before you can marshal them in .NET.
The basic idea of instantiating a C++ object from .NET world is to allocate exact size of the C++ object from .NET, then call the constructor which is exported from the C++ DLL to initialize the object, then you will be able to call any of the functions to access that C++ object, if any of the method involves other C++ classes, you will need to wrap them in a C# class as well, for methods with primitive types, you can simply P/Invoke them. If you have only a few methods to call, it would be simple, manual coding won't take long. When you are done with the C++ object, you call the destructor method of the C++ object, which is a export function as well. if it does not have one, then you just need to free your memory from .NET.
Here is an example.
public class SampleClass : IDisposable
{
[DllImport("YourDll.dll", EntryPoint="ConstructorOfYourClass", CharSet=CharSet.Ansi, CallingConvention=CallingConvention.ThisCall)]
public extern static void SampleClassConstructor(IntPtr thisObject);
[DllImport("YourDll.dll", EntryPoint="DoSomething", CharSet=CharSet.Ansi, CallingConvention=CallingConvention.ThisCall)]
public extern static void DoSomething(IntPtr thisObject);
[DllImport("YourDll.dll", EntryPoint="DoSomethingElse", CharSet=CharSet.Ansi, CallingConvention=CallingConvention.ThisCall)]
public extern static void DoSomething(IntPtr thisObject, int x);
IntPtr ptr;
public SampleClass(int sizeOfYourCppClass)
{
this.ptr = Marshal.AllocHGlobal(sizeOfYourCppClass);
SampleClassConstructor(this.ptr);
}
public void DoSomething()
{
DoSomething(this.ptr);
}
public void DoSomethingElse(int x)
{
DoSomethingElse(this.ptr, x);
}
public void Dispose()
{
Marshal.FreeHGlobal(this.ptr);
}
}
For the detail, please see the below link,
C#/.NET PInvoke Interop SDK
(I am the author of the SDK tool)
Once you have the C# wrapper class for your C++ class ready, it is easy to implement ICustomMarshaler so that you can marshal the C++ object from .NET.
http://msdn.microsoft.com/en-us/library/system.runtime.interopservices.icustommarshaler.aspx