I'm trying to pass a function pointer from C# into C++/CLI and getting a windows compiler error stating that the ManagedTakeCallback function is not supported by this language (C#)--I define the ManagedTakeCallback in the C++/CLI interop. My code looks like
C# application:
namespace ManagedConsoleApplication
{
class Callback
{
public delegate double DelegateAdd(double value1, double value2);
public static double CallbackAdd(double value1, double value2)
{
return value1 + value2;
}
public static DelegateAdd delegateCallback = new DelegateAdd(Callback.CallbackAdd); //declare as static to prevent GC
}
class Program
{
// [DllImport("InteropDLL.dll", CallingConvention = CallingConvention.StdCall)]
// public static extern void ManagedCallback(IntPtr pCallback);
static void Main(string[] args)
{
InteropDLL io = new InteropDLL();
Console.WriteLine("The Add return = {0}", io.ManagedAdd(3, 2));
Console.WriteLine("Pass CallBack to Unmanaged code");
Callback cb = new Callback();
IntPtr intptr_delegate = Marshal.GetFunctionPointerForDelegate(Callback.delegateCallback); //convert delegate to function pointer which can be used by unmanaged code
Console.WriteLine("The callback return is {0}", io.ManagedTakeCallback(intptr_delegate));
Console.WriteLine("Please hit Enter to exit");
String value = Console.In.ReadLine();
//Console.WriteLine("End of program ", value);
}
}
}
and,
C++/CLI interop dll h and cpp file:
//HEADER
namespace Interop
{
typedef double (__stdcall *PCallback)(double value1, double value2);
public ref class InteropDLL
{
public:
double ManagedAdd(double value1, double value2);
public:
double ManagedTakeCallback(PCallback pCallback);
};
}
//CPP
double Interop::InteropDLL::ManagedAdd(double value1, double value2)
{
return NativeAdd(value1, value2);
}
double Interop::InteropDLL::ManagedTakeCallback(PCallback pCallback)
{
return NativeTakeCallback();
}
The C++/CLI interop layer then calls a C DLL. I'm able to call ManagedAdd interop function; however, if ManagedTakeCallback is added, there is a windows compiler error. I suspect that the C# application is not marshaling in the function pointer correctly via ManagedTakeCallback function or that the signature is not correct on the C++/CLI side? I would greatly appreciate any insight.
Here is comment from on site:
"But C# doesn’t suport C++ function pointer, so we cannot invoke a C++ function pointer here. C# only has Delegate objects and we have to convert the function pointer to Delegate by Marshal.GetDelegateForFunctionPointer. It is declared in System.Runtime.InteropServices as follows:
public static Delegate GetDelegateForFunctionPointer (
IntPtr ptr,
Type t)
for full answer look at link:
http://www.codeproject.com/Articles/27298/Dynamic-Invoke-C-DLL-function-in-C
Related
I'm currently working on a .NET Framework 4.7.2 application using a business logic library written in unmanaged C++. I need to use unmanaged C++.
I need to use the logic from the C++ project, unfortunately I cannot correctly convert the input or output parameters of my program.
When I input 42, and simply want to return that value, I get 17582022 as a result. Which should actually be 42.
My C++ code looks like that:
MYCore header file:
#ifdef MYCORE_EXPORTS
#define MYCORE_API __declspec(dllexport)
#endif
#pragma once
#include <string>
using namespace std;
extern "C"
{
class MYCORE_API TestClass
{
private:
string name;
public:
TestClass(char*);
long Iterate(long &n);
};
MYCORE_API TestClass* TestClass_Create(char* name);
}
MYCore source file:
#include "stdafx.h"
#include "MYCore.h"
TestClass::TestClass(char* n)
{
name = n;
}
long TestClass::Iterate(long &n)
{
return n;
}
extern "C"
{
MYCORE_API TestClass * TestClass_Create(char* name)
{
return new TestClass(name);
}
}
I'm using a .NET 4.7.2 Framework Interface project to export the C++ library functionality:
namespace MYCore.Interface
{
public static class MYProxy
{
private const string coreDLL = "my.core.dll";
[DllImport(coreDLL, CallingConvention = CallingConvention.Cdecl)]
public static extern IntPtr TestClass_Create(string name);
[DllImport(coreDLL, EntryPoint = "?Iterate#TestClass##XXXXX#X", CallingConvention = CallingConvention.ThisCall)]
public static extern int Iterate(int n);
}
}
In my actual application I further import the dll and use the logic like that:
public static void Initialize()
{
var test = MYProxy.WrapperIterator_Create("test");
var result = MYProxy.Iterate(42); // as a result I'm getting sth. like 17582022 instead of 42
}
Do you know how to correctly convert an int input from C# to C++ and vice versa?
Thank you!
What you're doing in C# does not work in C++ either:
auto result = Iterate(42l);
results in the compiler error
Cannot convert argument 1 from 'long' to 'long &'
I see two solutions:
a) Change the C++ code
long TestClass::Iterate(long n)
(without the reference)
b) Change the C# code
static extern int Iterate(ref int n);
(pass a reference) and call it like
int n = 42;
Console.WriteLine(Iterate(ref n));
The problem is actually called "Marshal an unmanaged C++ Class to C#".
In my Proxy class I created a method to call an actual instance method:
[DllImport(coreDLL, EntryPoint = "?Iterate#TestClass##XXX#X", CallingConvention = CallingConvention.ThisCall)]
public static extern int CallIterate(IntPtr instance, int n);
and the method in my C++ looks like that:
MYCORE_API int CallIterate(TestClass * instance, int n)
{
if (instance!= NULL)
{
return instance->Iterate(n);
}
}
For further reading on how to marshal unmanaged C++ classes, I can suggest the following article:
https://www.codeproject.com/Articles/18032/How-to-Marshal-a-C-Class
My solution works fine now. Thanks for all the good input!
I have an unmanaged DLL that exports only a C style factory method that returns a new instance of a class (simplified here to look simple).
hello.h
#if defined(HWLIBRARY_EXPORT) // inside DLL
# define HWAPI __declspec(dllexport)
#else // outside DLL
# define HWAPI __declspec(dllimport)
#endif
struct HelloWorld{
public:
virtual void sayHello() = 0;
virtual void release() = 0;
};
extern "C" HWAPI HelloWorld* GetHW();
hello.cpp
#include "hello.h"
struct HelloWorldImpl : HelloWorld
{
void sayHello(){
int triv;
std::cout<<"Hello World!";
std::cin>>triv;
};
void release(){
this->HelloWorldImpl::~HelloWorldImpl();
};
HelloWorld* GetHW(){
HelloWorld* ptr = new HelloWorldImpl();
return ptr;
};
Now, I can use dllimport to access GetHW() but is there a way to access the member functions of the returned 'struct'... ie, sayHello and release?
I was also stuck with the same problem. This question was asked a while before. I commented to it for any better solution but didn't get any reply yet. So, reposting it.
When i googled, able to find out two solutions.
Solution1: Expose all the member functions in the C-style for the existing dll. Which i cant do, as it is a 3rd party dll.
Solution2: Write a managed C++ dll exposing the functionality of native C++ dll, which later can be used in your C# dll. Here many classes/functions are present. So, creating would take most of the time.
i got the above solutions from the link below.
How To Marshall
Please let me know if there is any better solution other than the above two solutions?
i have the source code for C++ solution. But what i though was not to touch C++ dll. If there is any possibility to do it in C#, it would be great.
If there is no alternative, i need to follow any one of the specified two solutions.
The C++ code is using the way abstract classes are implemented by the Visual C++ compiler. http://blogs.msdn.com/b/oldnewthing/archive/2004/02/05/68017.aspx. This memory layout is "fixed" because it is used for implementing COM interfaces. The first member of the struct in memory will be a pointer to a vtable containing the function pointers of your methods. So for a
struct HelloWorldImpl : public HelloWorld
{
public:
int value1;
int value2;
}
the "real" layout in memory would be:
struct HelloWorldImpl
{
HelloWorldVtbl *vtbl;
int value1;
int value2;
}
where vtbl would be:
struct HelloWorldVtbl
{
void *sayHello;
void *release;
}
Just for the sake of doing a complete response, I'm writing the example for this signatures:
struct HelloWorld {
public:
virtual int sayHello(int v1, int v2, int v3) = 0;
virtual void release() = 0;
};
C# code:
[DllImport("NativeLibrary.dll", CallingConvention = CallingConvention.Cdecl)]
public static extern IntPtr GetHW();
[StructLayout(LayoutKind.Sequential)]
struct HelloWorldVtbl
{
public IntPtr sayHello;
public IntPtr release;
}
Your functions are void Func(void) or int Func(int, int, int), but in truth they have a hidden parameter, this, so you can write them as:
int sayHello(HelloWorld*, int, int, int);
void release(HelloWorld*);
so in C# the delegate is
[UnmanagedFunctionPointer(CallingConvention.ThisCall)]
public delegate int Int32MethodInt32Int32Int32(IntPtr ptr, int v1, int v2, int v3);
[UnmanagedFunctionPointer(CallingConvention.ThisCall)]
public delegate void VoidMethodVoid(IntPtr ptr);
Then you can use
IntPtr ptr = GetHW();
IntPtr vtbl = Marshal.ReadIntPtr(ptr, 0);
HelloWorldVtblhw = (HelloWorldVtbl)Marshal.PtrToStructure(vtbl, typeof(HelloWorldVtbl));
Int32MethodInt32Int32Int32 sayHello = (Int32MethodInt32Int32Int32)Marshal.GetDelegateForFunctionPointer(hw.sayHello, typeof(Int32MethodInt32Int32Int32));
int res = sayHello(ptr, 1, 2, 3);
Console.WriteLine(res);
VoidMethodVoid release = (VoidMethodVoid)Marshal.GetDelegateForFunctionPointer(hw.release, typeof(VoidMethodVoid));
release(ptr);
I am trying without success to write code in C# to pass a bitmap to an unmanaged c++ DLL and return a POINT structure.
I have done a lot of research on the internet, but have not found the "Gotcha" article or piece of code to help me resolve my issue.
The best I have been able to come up with so far is an unmanaged c++ DLL, wrapped with a managed c++ dll, called by my C# app. In testing that, I can pass simple types, such as an integer and return an integer with no problem. Now for the issue I am having, the bitmap.
I have tried passing an HBITMAP (using the GetHBitmap() function of my bitmap in c#), but I get errors during compile of "cannot convert parameter 1 from 'System::IntPtr' to 'HBITMAP'" and "Class1.FindImage(void *, void *) is inaccessible due to it's protection level".
Here is some of my code:
Main App:
class Program
{
[StructLayout(LayoutKind.Sequential)]
public struct POINT
{
public int X;
public int Y;
public POINT(int x, int y)
{
this.X = x;
this.Y = y;
}
public static implicit operator System.Drawing.Point(POINT p)
{
return new System.Drawing.Point(p.X, p.Y);
}
public static implicit operator POINT(System.Drawing.Point p)
{
return new POINT(p.X, p.Y);
}
}
static void Main(string[] args)
{
Image src = Image.FromFile("Pin.png");
Image tgt = Image.FromFile("screen.png");
Bitmap bsrc = new Bitmap(src);
Bitmap btgt = new Bitmap(tgt);
IntPtr bs = bsrc.GetHbitmap();
IntPtr bt = btgt.GetHbitmap();
POINT p = Class1.FindImage(bs, bt);
}
}
ImportWrap.h:
namespace ImportWrap {
public ref class Class1
{
public:
static POINT FindImage(IntPtr source, IntPtr target);
};
}
ImportWrap.cpp:
static POINT FindImage(IntPtr source, IntPtr target)
{
return ImgFuncs::MyImgFuncs::FindImage(source, target);
}
ImgFuncs.h
typedef long LONG;
typedef void *PVOID;
typedef PVOID HANDLE;
typedef HANDLE HBITMAP;
typedef struct tagPOINT {
LONG x;
LONG y;
} POINT, *PPOINT;
namespace ImgFuncs
{
class MyImgFuncs
{
public:
static __declspec(dllexport) POINT FindImage(HBITMAP source, HBITMAP target);
};
}
ImgFuncs.cpp
namespace ImgFuncs
{
POINT MyImgFuncs::FindImage(HBITMAP source, HBITMAP target)
{
POINT p;
p.x = 1;
p.y = 2;
return p;
}
}
What am I doing wrong, or am I going completely off the map with my approach?
I would GLADLY entertain any suggestions regarding the correct way to code what I am trying to do.
I have some C++ code that is used to find an image within another image that works quite fast. Unfortunately, even using lockbits in c#, it's not fast enough. So I would like to make use of the c++ code for the image search.
I am sure I will run into further snags, but might be able to handle it if I can get past this stumbling block. As you can see, my C++ knowledge is limited.
You cannot use native struct types as a return value, C# can't handle them. Casting from IntPtr to HBITMAP requires a double cast. Like this:
static System::Drawing::Point FindImage(IntPtr source, IntPtr target)
{
POINT retval = ImgFuncs::MyImgFuncs::FindImage((HBITMAP)(void*)source, (HBITMAP)(void*)target);
return System::Drawing::Point(retval.X, retval.Y);
}
Add an assembly reference to System.Drawing. You might then also want to consider passing a Bitmap^ instead of an IntPtr to make it even easier to use.
You could probably skip the managed C++ wrapper entirely and just call the unmanaged DLL from C# via P/Invoke. Put something like this in your C# class
[DllImport("YourUnamangedDll.dll")]
private static extern POINT FindImage(IntPtr source, IntPtr target);
I haven't tested this, so you may need to tweak it as needed, but that's the general idea.
I am trying to wrap a C++ function that has a reference parameter with C# code.
My C# wrapper class has
[DllImport(TestCppDLL.dll)]
public static extern void foo(out int a, out int b, out double c);
public void main()
{
int a;
int b;
double c;
this.foo(out a, out b, out c);
Console.WriteLine(a + b + c);
}
And my C++ code is
extern void foo(int &a, int &b, double &c)
{
a = 1;
b = 2;
c = 3;
}
So I expect the output to be "123" but I get "000".
How do I wrap C++ reference parameter?
Thank you in advance,
Your C++ code returns a double but your C# code declares the function as having void return value.
You also may have a calling convention mismatch. C++ default is cdecl, C# default is stdcall.
Otherwise it's fine.
Is it possible to call a c(++) static function pointer (not a delegate) like this
typedef int (*MyCppFunc)(void* SomeObject);
from c#?
void CallFromCSharp(MyCppFunc funcptr, IntPtr param)
{
funcptr(param);
}
I need to be able to callback from c# into some old c++ classes. C++ is managed, but the classes are not ref classes (yet).
So far I got no idea how to call a c++ function pointer from c#, is it possible?
dtb is right. Here a more detailed example for Marshal.GetDelegateForFunctionPointer. It should work for you.
In C++:
static int __stdcall SomeFunction(void* someObject, void* someParam)
{
CSomeClass* o = (CSomeClass*)someObject;
return o->MemberFunction(someParam);
}
int main()
{
CSomeClass o;
void* p = 0;
CSharp::Function(System::IntPtr(SomeFunction), System::IntPtr(&o), System::IntPtr(p));
}
In C#:
public class CSharp
{
delegate int CFuncDelegate(IntPtr Obj, IntPtr Arg);
public static void Function(IntPtr CFunc, IntPtr Obj, IntPtr Arg)
{
CFuncDelegate func = (CFuncDelegate)Marshal.GetDelegateForFunctionPointer(CFunc, typeof(CFuncDelegate));
int rc = func(Obj, Arg);
}
}
Have a look at the Marshal.GetDelegateForFunctionPointer method.
delegate void MyCppFunc(IntPtr someObject);
MyCppFunc csharpfuncptr =
(MyCppFunc)Marshal.GetDelegateForFunctionPointer(funcptr, typeof(MyCppFunc));
csharpfuncptr(param);
I don't know if this really works with your C++ method, though, as the MSDN documentation states:
You cannot use this method with function pointers obtained through C++