I have an unmanaged dll with a class "MyClass" in it.
Now is there a way to create an instance of this class in C# code? To call its constructor? I tried but the visual studio reports an error with a message that this memory area is corrupted or something.
Thanks in advance
C# cannot create class instance exported from native Dll. You have two options:
Create C++/CLI wrapper. This is .NET Class Library which can be added as Reference to any other .NET project. Internally, C++/CLI class works with unmanaged class, linking to native Dll by standard C++ rules. For .NET client, this C++/CLI class looks like .NET class.
Write C wrapper for C++ class, which can be used by .NET client with PInvoke. For example, over-simplified C++ class:
class MyClass()
{
public:
MyClass(int n){data=n;}
~MyClass(){}
int GetData(){return data;}
private:
int data;
};
C API wrapper for this class:
void* CreateInstance()
{
MyClass* p = new MyClass();
return p;
}
void ReleaseInstance(void* pInstance)
{
MyClass* p = (MyClass*)pInstance;
delete p;
}
int GetData(void* pInstance)
{
MyClass* p = (MyClass*)pInstance;
return p->GetData();
}
// Write wrapper function for every MyClass public method.
// First parameter of every wrapper function should be class instance.
CreateInstance, ReleaseInstance and GetData may be declared in C# client using PInvoke, and called directly. void* parameter should be declared as IntPtr in PInvoke declaration.
The solution is create C++/CLI wrapper like:
#include "DllExportClass.h"
public ref class ManagedOperationHelper
{
public:
double Sum(double add1, double add2)
{
CDllExportClass obj;
double ret=obj.Sum(add1, add2);
return ret;
}
double Mult(double mult1, double mult2)
{
CDllExportClass obj;
double ret=obj.Mult(mult1, mult2);
return ret;
}
};
where CDllExportClass is the class exported from native code. Above is the .h of the C++/CLI. Take care to let find the lib to this dll. Put the dll and the lib in the same directory and compile the C++/CLI code.In the managed code directory put the native dll and the C++/CLI dll. In the managed project put the reference of the C++/CLI project. Instanciate in the maged code the C++/CLI class like:
ManagedOperationHelper obj = new ManagedOperationHelper();
double ret=obj.Sum(10, 20);
It's all.
You can not use unmanged C++ code directly in C#. The interoperability can be done using PInvoke. There are a lot of issues related to this topic, especially when calling functions which have pointers as arguments.
The basic procedure goes like this:
C# part
namespace MyNamespace {
public class Test {
[DllImport("TheNameOfThe.dll")]
public static extern void CreateMyClassInstance();
public void CallIt() {
CreateMyClassInstance(); // calls the unmanged function via PInvoke
}
}
}
C++ part
class MyClass {
public: MyClass() { /** Constructor */ }
};
MyClass* staticObject;
extern "C" void CreateMyObjectInstance() {
staticObject = new MyClass(); // constructor is called
}
Related
Apologize for my very basic knowledge of C++/CLI, but it has only been introduced to me recently as a necessity. I am trying to create a wrapper for an unmanaged C++ library using C++/CLI. I have followed this helpful guide and can confirm that it (somehow) does the trick. The problem I have is with C++ pointers which expose access to public classes in the unmanaged library. In my CPP library I used them to call the methods from several classes, by having access to a single point-of-entry class. In C# I can't access the methods which should be accessible via these class pointers. I am getting an error stating "the member is inaccessible due to its protection level" and the "->" pointer does not grant access to the exposed class members.
Here's what my code looks like:
UnmanagedCode::ClassA
...
// some code
...
public:
void doSomething() { ... };
ClassB* classB() { return classB.get(); };
private:
std::unique_ptr<ClassB> classB_ {};
C++/CLI wrapper
public ref class WrapperClass: public ManagedObject<UnmanagedCode::ClassA>
{
public:
WrapperClass() : ManagedObject(new UnmanagedCode::ClassA) {}; // template class code in the hyperlink
~WrapperClass() {};
void doSomething() { m_Instance->doSomething(); };
UnmanagedCode::ClassB* classB() { return m_Instance->classB(); };
};
C# program
class Program
{
static void Main(string[] args)
{
WrapperClass w = new WrapperClass();
w.doSomething(); // this works fine
w.classB(); // here is where I am getting the error
}
}
My C# knowledge, is not quite as good as my C++, just as a note.
I dont quite get what you are doing here:
UnmanagedCode::ClassB* classB() { return m_Instance->classB(); };
This line returns a pointer to a ClassB object, that you retrieve in C#. This would require the ClassB to also be a managed object, as far as i know, otherwise, i dont think you can call functions on the object, without creating delegates for unsafe function pointers.
If i understand your issue correct, i think something like this, would fix your issue, in C++:
void* classB() { return static_cast<void*>(m_Instance->classB()); };
void doSomethingWithClassB(void* instance) {static_cast<ClassB*>(instance)->doSomethingWithClassB();}
and then in C#:
class Program
{
static void Main(string[] args)
{
WrapperClass w = new WrapperClass();
w.doSomething();
unsafe
{
void* classb = w.classB();
w.doSomethingWithClassB(classb);
}
}
I think you need to provide a wrapper for each class to make it useful in c#.
I.e. to return the classB you would write something like
MyClassBWrapper^ GetClassB(){ return gcnew MyClassBWrapper(m_Instance->classB());
While you can mess around with pointers in managed code, it requires unsafe code, and is quite cumbersome to use. If you are writing a c++/cli wrapper anyway you should provide a fully managed API. With the possible exception of (optionally) using pointers for large data blocks like images or similar.
I have c++ dll:
UnmanagedCode.h looks like:
#include "stdafx.h"
struct Class1
{
public: virtual void method() = 0;
};
extern "C" __declspec(dllimport) Class1* Create_function();
UnmanagedCode.cpp looks like:
#include "stdafx.h"
#include "UnmanagedCode.h"
class Class2 : Class1
{
public: void method(){}
};
Class1* Create_function()
{
Class2* c2 = new Class2(); // I don't care about free memory for this example
Class1* c1 = (Class1*)c2;
return c1;
};
I have c++/cli managed class:
#include "Library.h"
#include "UnmanagedCode.h"
typedef Class1* (*Createfunction)();
namespace CLIWrapper
{
public ref class ManagedClI
{
private:
Class1* cl1;
public:
ManagedClI(){}
void Create()
{
//some usual routine for loading c++ library with Library class
String ^path = "path to the library.dll"; // just to show
using System::Runtime::InteropServices::Marshal;
const char* cpath = (const char*)(Marshal::StringToHGlobalAnsi(path)).ToPointer();
Library loader;
loader.load((string)cpath, false);
Marshal::FreeHGlobal(System::IntPtr((void*)cpath));
Createfunction hDet = (Createfunction)loader.getProcAddress("Create_function");
cl1 = hDet();
cl1->method(); // if I call cl1->method() here it works perfect!!
}
void SomeFunction()
{
cl1->method(); //but if I call cl1->method() here it throws an error!!!
}
};
}
I use ManagedClI class in my c# application, Something like:
CLIWrapper.ManagedClI object = new CLIWrapper.ManagedClI();
object.Create();
object.SomeFunction(); // <- this causes an error
object.SomeFunction() causes the error: attempted to read or write protected memory when it calls cl1->method().
But in the same time cl1->method() is normally working in Object.Create().
I think that I'm doing something wrong when wrapping Create_function().
Can anyone suggest something?
Your Library loader is more than just a loader. It is the CLI object that keeps the DLL loaded. When the last reference to it goes away and it is cleaned up, the DLL is unloaded.
The virtual function table of your abstract class lives in that DLL, as does the functions that it points to. When the DLL is unloaded, that virtual function table becomes invalid, and attempting to call the method is going to be undefined behavior.
To fix this in a first approximation, store the Library object in your ManagedClI class instead of as a local variable.
I have a C# dll ( for which register for COM interop option is set).
This C# dll has the below interface and class
interface IMyInterface
{
bool IsNameExists(string name);
List<string> GetNameList();
}
public class MyClass : IMyInterface
{
public bool IsNameExists(string name)
{
//DO Something
}
public List<string> GetNameList()
{
// DO something
}
}
I need to call the methods IsNameExists and GetNameList from unmanaged C++.
#import "..\..\ProdCon\bin\ProdCon.tlb" raw_interfaces_only
void main()
{
HRESULT hr =::CoInitialize(NULL);
IMyInterface pIMyInterface(__uuidof(MyClass));
VARIANT_BOOL bRet = FALSE;
BSTR bstrName = ::SysAllocString(_T("RAJESH"));
hr = pIMyInterface->IsNameExists(bstrName,&bRet);
}
So I created COM object as above and called the IsNameExists mehtod without any issue.
Since GetNameList method returns list, I am getting the below warning
'MyDll.IMyInterface.GetNameList(#0), MyDll'. Warning: Type library
exporter encountered a generic type instance in a signature. Generic
code may not be exported to COM.
Please help me how to return C# list to unmanaged C++ code. So that unmanaged C++ code can use this list.
'Generic code may not be exported to COM.' => hence its the type parameter string in public List GetNameList(). Thus essentially you need access to a non-generic c# method to get the data.
If you have control of the MyClass codebase you could (for example) add a:
public string[] GetNameArray()
{
return GetNameList.ToArray();
}
If not then you'll need to write a proxy/wrapper class to do something similar to the above and expose that via COM, either as a one off or a 'general' methodology using reflection say.
See for example http://weblog.west-wind.com/posts/2007/Jul/10/Generics-and-COM-Interop-dont-mix
I've got a C++/CLI project that wraps a large number of classes - and the classes have their own meta-data system. So I'd like to return a dynamic object to make some use cases easy in C#. But I don't see how to do this in C++.
In C# I can write the following:
dynamic TestThisOut()
{
return null;
}
void mork()
{
var d = TestThisOut();
d.Fork();
}
I would like to write TestThisOut() in C++/CLI, so that I can use it exactly the same way as I do in the "mork" function above (i.e. not having to type the dynamic keyword). Is this possible?
You can create a dynamic object in c++/cli, you just can't consume it there as you would in C# project. However you can consume it from C#. Here is how you do it:
In C++/CLI create a property or a method that returns Object^. Mark this property or method with System::Runtime::CompilerServices::DynamicAttribute. You are good to go.
Here is a quick sample I created:
namespace ClassLibrary1
{
using namespace System;
using namespace System::Dynamic;
public ref class Class1 : public DynamicObject
{
public:
[System::Runtime::CompilerServices::Dynamic]
static property Object^ Global
{
public:
Object^ get()
{
return gcnew Class1();
}
}
public:
String^ Test()
{
return "Test";
}
};
}
And my C# consumer:
Console.WriteLine( ClassLibrary1.Class1.Global.Test() );
dyanmic is C# 4.0 keyword. It is not supported in C++ CLI (and also in VB.NET).
If you want to consume dynamic object in C++ CLI, then you can use impromptu-interface library. List of supported options. Information is from this question
I have an native C++ dll, some header files and the import library. Is there a way how to instantiate an object within C# that is defined in the dll?
The two ways I'm aware of are:
to wrap the C++ code into COM
to use DLLImport and external C functions
C++/CLI is your friend for this. You'll run into one problem though: it is not possible to store standard C++ objects inside C++/CLI ref or value classes (the ones for .NET). So you'll have to resort to the following class (that you can modify) that I use in production code:
#pragma once
#include <boost/shared_ptr.hpp>
template <typename T>
ref class Handle
{
boost::shared_ptr<T>* t;
!Handle()
{
if (t != nullptr)
{
delete t;
t = nullptr;
}
}
~Handle() { this->!Handle(); }
public:
Handle() : t(new boost::shared_ptr<T>((T*)0)) {}
Handle% operator=(T* p)
{
if (p != t->get()) t->reset(p);
return *this;
}
static T* operator&(Handle% h) { return h.t->get(); }
static boost::shared_ptr<T> operator->(Handle% h) { return *h.t; }
T& reference() { return *t->get(); }
T const& const_reference() { return *t->get(); }
};
Usage: Handle<MyCppClass>^ handle; inside a C++/CLI class. You then implement stub methods, forwarding them to the handle member. Garbage collected objects will call destructors of the C++ class instance iff there is no more pointer to it:
public ref class Foo
{
void bar() { handle->bar(); }
internal:
Handle<CppNamespace::Foo>^ handle;
};
I think that your option is only build a C++/CLI class wrapper (so you can reference it like a c# class), otherwise you can't instantiate a c++ class (unmanaged) from c# code.
Alternative could be the "ugly" way: instantiate the c++ class through a c function, but you'll treat the class as a void pointer inside the c# code, so you basically will not do anything with it (except if you create other functions to interact with this class; only C functions)
C# understands C, if you want make it understand C++ you have to use C++/CLI
P.S.
C# has some basic understanding of C++ classes, but it's only about converting class data (I mean bytes: fields) into some usable data in C# (there are some Attributes), but will not allow to work with methods and things like that (avoid totally is my suggestion).