I have an unmanaged dll that contains a function to read a data from a file. I wrote a CLI wrapper for it.
To test whether it is working, I wrote a simple CLI program calling the wrapper class and the data read method. It worked fine.
I used that dll in a c# program but the data is not read properly. It reads but the data read is not proper.
CLI function:
void FileReader::ReadFile()
{
int ret;
STRUCT head;
STRUCT1 *sqar;
memset ( ( void * )&head, 0, sizeof ( STRUCT) );
sqar = ( STRUCT1 * )NULL;
ret = Read_func( "somefile.someformat", &head, &sqar );
}
CLI EXE:
int main(array<System::String ^> ^args)
{
FileReader reader;
reader.ReadFile();
Console::WriteLine(L"Hello World");
return 0;
}
This works fine. When I debug, the code flows through and reads the data properly.
C# code:
{
FileReader filereader= new FileReader ();
filereader.ReadFile();
}
When I import the CLI dll in the C# project and access the code as above the data in not read properly.
STRUCT has int as members and it is read properly.STRUCT1 has int, double and structure pointers as members which is not read properly. What could be possibly wrong?
The solution was to change the Struct Member Alignment property under C/C++ > Code Generation from 1byte 1 byte /Zp1 to Default. Simple.
Related
I have a computer vision plugin using Hololens locatable camera on Unity 5.2. I use the class UnityEngine.XR.WSA.WebCam.PhotoCaptureFrame with photo mode enabled at highest resolution, which is 2048x1156, in NV12 color format which is camera native format.
PhotoCaptureFrame class : https://docs.unity3d.com/2017.2/Documentation/ScriptReference/XR.WSA.WebCam.PhotoCaptureFrame.html
At the moment, I do this for my plugin to process any single photo:
PhotoCaptureFrame photo; // created correctly through Unity API
List<byte> photoBuffer = new List<byte>();
photo.CopyRawImageDataIntoBuffer(photoBuffer);
// marshal photoBuffer to plugin (and it works fine for the computer vision part)
However, it copies the raw buffer each time. I want to use the raw buffer directly from my plugin. So I tried this:
IntPtr rawBufferPtr = photo.GetUnsafePointerToBuffer(); // COM pointer to IMFMediaBuffer is incremented
// send rawBufferPtr to plugin (native function described below)
Marshal.Release(rawBufferPtr);
IMFMediaBuffer interface : https://msdn.microsoft.com/en-us/library/windows/desktop/ms696261(v=vs.85).aspx
And in my C++ plugin:
#include <Mfidl.h> // for IMFMediaBuffer support
void process_photo(void *photo_buffer_wrapper, int photo_width, int photo_height)
{
// photo_buffer_wrapper = rawBufferPtr in managed environment
IMFMediaBuffer *media_buffer = reinterpret_cast<IMFMediaBuffer *>(photo_buffer_wrapper);
BYTE *photo_buffer = NULL;
HRESULT result = media_buffer->Lock(&photo_buffer, NULL, NULL);
if (SUCCEEDED(result))
{
// do image processing stuff here (with OpenCV) using photo_buffer
media_buffer->Unlock;
}
}
It appears fine to me. It does compile fine too. But at run time, I get an access violation and the applications crashes on Hololens.
Exception Code: 0xC0000005
Exception Information: The thread tried to read from or write to a virtual address for which it does not have the appropriate access.
Anyone sees the problem? Something to do with the way I pass the IMFMediaBuffer object from managed to unmanaged environment?
Thank you very much!
I will answer my own question.
The photo_buffer_wrapper is not a pointer to IMFMediaBuffer as I thought but a pointer to IUnknown. Here is the modified native function that works as intended:
// UNMANAGED ENVIRONMENT
#include <Mfidl.h> // for IMFMediaBuffer support + other COM stuff
void process_photo(void *photo_buffer_unknown, int photo_width, int photo_height)
{
// photo_buffer_unknown = photoCaptureFrame.GetUnsafePointerToBuffer() in managed environment which is an IntPtr
IMFMediaBuffer *media_buffer;
if (SUCCEEDED(reinterpret_cast<IUnknown *>(photo_buffer_unknown)->QueryInterface<IMFMediaBuffer>(&media_buffer)))
{
BYTE* photo_buffer = NULL;
if (SUCCEEDED(media_buffer->Lock(&photo_buffer, NULL, NULL)))
{
// process photo_buffer with OpenCV (wrapped in a cv::Mat)
media_buffer->Unlock();
media_buffer->Release(); // QueryInterface on IUnknown has incremented reference count by one
}
}
}
NB: The pointer returned from photoCaptureFrame.GetUnsafePointerToBuffer() still has to be released in managed environment like in my question:
// MANAGED ENVIRONMENT
IntPtr mediaBufferUnknownPtr = photoCaptureFrame.GetUnsafePointerToBuffer();
// send mediaBufferUnknownPtr to native function through extern DLL call
Marshal.Release(mediaBufferUnknownPtr)
I have been trying for the past 4 hours to solve a very mysterious problem.
I am writing some plugin for Notepad++. To achieve syntax highlighting one has to export such a function:
//this function is exported via exports.def file
LexerFactoryFunction SCI_METHOD GetLexerFactory(unsigned int index)
{
return (index == 0) ? RTextLexer::LexerFactory : nullptr;
}
where,
LexerFactoryFunction is typedef ILexer *(*LexerFactoryFunction)();
#define SCI_METHOD __stdcall
I have managed to get this thing working perfectly with C++, however another part of the plugin is written in C#, so I tried to merge the two using Fody Costura NuGet package ( so that the CLI .dll is embedded into the main .dll ), however with no success.
What I've tried :
public ref class RTextLexerCliWrapper
{
public:
delegate ILexer * GetLexerFactoryDelegate();
IntPtr GetLexerFactory()
{
return System::Runtime::InteropServices::Marshal::GetFunctionPointerForDelegate(_lexerFactoryPtr);
}
RTextLexerCliWrapper();
private:
GetLexerFactoryDelegate ^ _lexerFactoryPtr;
GCHandle gch;
~RTextLexerCliWrapper();
};
RTextLexerCliWrapper::RTextLexerCliWrapper()
{
_lexerFactoryPtr = gcnew GetLexerFactoryDelegate(&RTextLexer::LexerFactory);
gch = GCHandle::Alloc(_lexerFactoryPtr);
}
RTextLexerCliWrapper::~RTextLexerCliWrapper()
{
gch.Free();
}
This CLI wrapper, is referenced in my main .dll like this :
static RTextLexerCliWrapper _lexerWrapper = new RTextLexerCliWrapper();
[DllExport(CallingConvention = CallingConvention.Cdecl)]
static IntPtr GetLexerFactory(uint index)
{
return (index == 0) ? _lexerWrapper.GetLexerFactory() : IntPtr.Zero;
}
So what happens is, my .net function gets indeed called and the cli wrapper function is also called, and a function pointer is indeed returned. However any attempts to call that function pointer results in an access violation. Which means that either the type of the pointer is wrong or something else which I am currently missing. I have tried countless variations of the .net exported function with void *, StdCall etc. All result in the same problem.
Is there any other way to return a function pointer of a C++ class? Or well am I doing something completely wrong?
Thanks in advance!
So I have finally managed to found the solution to my problem.
First step was exporting the functions with the correct calling convention:
static RTextLexerCliWrapper _lexerWrapper = new RTextLexerCliWrapper();
[DllExport(CallingConvention = CallingConvention.StdCall)]
static IntPtr GetLexerFactory(uint index)
{
return (index == 0) ? _lexerWrapper.GetLexerFactory() : IntPtr.Zero;
}
The convention in this case had to be StdCall. Otherwise the stack pointer is invalidated, hence the exceptions.
Now in order to return a function pointer of a C++ instance things were a bit more tricky.
I am statically storing an instance of the CLI wrapper class so that it doesn't get GCed. ( _lexerWrapper ).
This instance has a function called GetLexerFactory which return a function pointer of the C++ instance ( which is then used by some other .dll to get actual instances of some object ).
The CLI Wrapper class looks like this:
public ref class RTextLexerCliWrapper
{
public:
delegate ILexer * GetLexerFactoryDelegate();
IntPtr GetLexerFactory()
{
return System::Runtime::InteropServices::Marshal::GetFunctionPointerForDelegate(_lexerFactoryPtr);
}
RTextLexerCliWrapper();
private:
GetLexerFactoryDelegate ^ _lexerFactoryPtr;
GCHandle gch;
~RTextLexerCliWrapper();
};
Where ILexer * is the type of the object we shall be returning later on.
RTextLexerCliWrapper::RTextLexerCliWrapper()
{
_lexerFactoryPtr = gcnew GetLexerFactoryDelegate(&RTextLexer::LexerFactory);
gch = GCHandle::Alloc(_lexerFactoryPtr);
}
RTextLexerCliWrapper::~RTextLexerCliWrapper()
{
gch.Free();
}
So, what we have managed here is, exporting through .NET a function pointer which is able to return a pure C++ object.
I am trying to pass struct as a parameter from C# application to the C++ MFC DLL. DLL fills records in the struct object and return back to the C# application. So here I used "out" keyword in C# application to call C++ method. When I execute it, it fails with error "Attempted to read or write protected memory. This is often an indication that other memory is corrupt." I am allocating memory at C++ DLL to store the records and assign it to out parameter. I could send data in struct object and print it in C++ DLL but not able to do modification in struct object at DLL side and return back to C# application.
Could anybody please help on this.
NativeDLLHelper.cs
class NativeDLLHelper
{
const int FIELD_LENGTH = 255;
[StructLayout(LayoutKind.Sequential)]
public struct APPDATA
{
public int ID;
public int Version;
[MarshalAs(UnmanagedType.LPTStr, SizeConst = FIELD_LENGTH)]
public string AppName;
};
[DllImport("Parser.dll", EntryPoint = "?FillLstStructData#DLLWrapper##QAEXAAPAU_APPDATA#1##Z")]
public static extern void FillLstStructData(out APPDATA[] AppDataStruct);
}
Main.cs
NativeDLLHelper.APPDATA[] lstFillAppDataStruct;
NativeDLLHelper.FillLstStructData(out lstFillAppDataStruct);
for (int i = 0; i < lstFillAppDataStruct.Length; i++)
{
Console.WriteLine(" ID[{0:G}]:{1:G}", i, lstFillAppDataStruct[i].ID);
Console.WriteLine(" Version[{0:G}]:{1:G}", i, lstFillAppDataStruct[i].Version);
Console.WriteLine(" AppName[{0:G}]:{1:G}", i, lstFillAppDataStruct[i].AppName);
}
C++ DLL:
static const int FIELD_LENGTH = 128;
typedef struct _APPDATA
{
int ID;
double Version;
TCHAR AppName[FIELD_LENGTH];
}APPDATA;
extern "C" __declspec(dllexport) FillLstStructData(APPDATA* &pAppData)
{
APPDATA *localAppDataStruct = new APPDATA[2];
localAppDataStruct[0].ID = 1;
localAppDataStruct[0].Version = 1.1;
_tcscpy(localAppDataStruct[0].AppName, L"MS Visual Studio 2010");
localAppDataStruct[1].ID = 2;
localAppDataStruct[1].Version = 2.1;
_tcscpy(localAppDataStruct[1].AppName, L"MS Office 2010");
pAppData = localAppDataStruct;
}
Your exported function unmangles to:
void __thiscall DLLWrapper::FillLstStructData(struct DLLWrapper::_APPDATA * &)
That makes it an instance method of a C++ class. You cannot pinvoke such methods, they require the C++ object to be created first and you cannot do this reliably with pinvoke. Only static C++ member functions can be pinvoked. Do note that this function doesn't need to be an instance method at all, it doesn't actually use instance members of the class.
That isn't the only problem, there's also a nasty memory management issue. The function allocates memory with ::operator new and memory needs to be released by the caller. But a C# program cannot do this, it doesn't have access to the ::operator delete that the C++ code uses. This kind of function is very hard to use reliably from a C++ program for that reason, it doesn't get better when you do it from C#. The proper way to do it is to allow the caller to pass the array. In other words, APPDATA[] and an extra argument that says how long the passed array is.
If you can't rewrite this function then you must write a wrapper for this class using the C++/CLI language. Very important that this wrapper uses the exact same compiler and CRT version as the C++ DLL.
I need to send a struct from C# managed code to a C library. The C library will populate the values in the struct. I have been trying to pass the struct as a reference so that the C# code will get the updated data values.
This is an example C function in libshlib.so:
void sharedStruct(struct data* d)
{
d->number = calcSomething();
d->message = doSomething();
}
I can send individual parameters (int and StringBuilder) and the library code runs and returns new values to the C# code that called it.
But how can I create a struct in C# that contains both int and string and send it to the unmanaged code (C library) which will populate the values to be used back in the C# code?
The C struct might be like this:
struct data
{
int number;
char* message;
};
Right now I'm trying to establish the best way to manipulate data in the C library for use in C#. I am writing both pieces of code so I am flexible but right now I haven't been able to get it working.
If you want the struct to be populated by the C code, then you are probably looking for an out variable. Note that the mono runtime by default will use free() to deallocate any strings you pass in and you might have to take extra care with padding in structures (see the StructLayout stuff in msdn). For strings, further problems can be had with character sets.
Sample code:
Managed.cs:
using System;
using System.Runtime.InteropServices;
struct Data
{
public int number;
public string message;
}
class Managed
{
[DllImport("unmanaged")]
extern static void Foo(out Data data);
static void Main()
{
Data data;
Foo(out data);
Console.WriteLine("number = {0}, message = {1}", data.number, data.message);
}
}
unmanaged.c:
#include <string.h>
struct data
{
int number;
char* message;
};
void Foo(struct data* data)
{
data->number = 42;
data->message = strdup("Hello from unmanaged code!");
}
Test run:
$ mcs Managed.cs
$ gcc -shared -fPIC -o libunmanaged.so unmanaged.c
$ LD_LIBRARY_PATH=$PWD mono Managed.exe
number = 42, message = Hello from unmanaged code!
I'm working on a c++ project which uses a string path to call an XML file. When i compiled the c++ everything works perfectly and i'm able to use the XML file as my project requires.
I needed to use a C# GUI, so i made a wrapper to call all my functions from my C++ file. One problem arises after debugging between the both platforms, c# does not recognize the string path to call my file, the error that i got is that it can not find the given path. Does anyone know how to send a valid string path between both platforms?
Thanks in advance,
Carolina
int ClassUnmanaged::ReadFile(string path_to_file)
{
int status = XMLClass->ReadConfigFile(path_to_file);
if(status)
{
return status; //Error
}
else
{
return 0;
}
}
Wrapper.h for the C++ class
public __gc class Wrapper
{
public: Wrapper(void);
public: ~Wrapper(void);
/** Unmanaged pointer to Class Unmanaged API
*
*/
private: ClassUnmanaged__nogc* pointerUnmanaged;
public: int NewReadfile(string path_to_file);
}
Wrapper.cpp
int Wrapper::NewReadFile(string path)
{
pointerUnmanaged->ReadFile(path);//here i access to my class unmanaged
return 0;
}
UI.cs
In the UI.cs i can not call the function NewReadfile from the wrapper because of the string type that c++ uses. Any idea how to solve this?
You will need to change the NewReadFile method to public and then change it to take as input a type that C# know about like Sytem::String it should look like this (using the new managed C++ syntax adapt to the old one if needed)
int Wrapper::NewReadFile(System::String^ path)
{
char* pathAsCharArray = (char*)(void*)Marshal::StringToHGlobalAnsi(str);
try
{
std::string pathAsStdString(pathAsCharArray);
pointerUnmanaged->ReadFile(pathAsStdString);
}
finally
{
Marshal::FreeHGlobal(pathUnmanaged);
}
return 0;
}
There is a KB article named "How to convert from System::String* to Char* in Visual C++" that explain the concept. If your underlying API could support unicode and you use the new syntax a better way to do the conversion is something like :
pin_ptr<const wchar_t> pathAsCharArray = PtrToStringChars(path);
std::wstring pathAsStrign(pathAsCharArray);