I currently have a simple unmanaged C++ method which just displays a messageBox. I have created a managed c++ wrapper for this, which I then reference in my c# application.
I need to be able to pass strings and other variables from the c# into the unmanaged c++ and back again but I am having trouble with the conversion of the strings as my c++ knowledge is very basic.
My end goal is to be able to call complicated functions from our legacy unmanaged c++ libraries via my new c# app (not using DLLImport or COM) but I am trying to create a simple example before progressing.
Thanks in advance.
Rich
Assuming the unmanaged C++ method looks something like this:
namespace UnmanagedCpp
{
class MessageBox
{
public:
static void Show(LPCTSTR lpszMessage)
{
::MessageBoxW(NULL, lpszMessage, L"Message", 0);
}
};
}
You could wrap it in something like this:
using namespace System::Runtime::InteropServices;
namespace ManagedCpp
{
public ref class MessageBox
{
public:
static void Show(String^ message)
{
#if defined(UNICODE) || defined(_UNICODE)
IntPtr intPtr = Marshal::StringToHGlobalUni(message);
#else
IntPtr intPtr = Marshal::StringToHGlobalAnsi(message);
#endif
UnmanagedCpp::MessageBox::Show(static_cast<LPTSTR>(intPtr.ToPointer()));
Marshal::FreeHGlobal(intPtr);
}
};
}
If you're planning on doing more extensive interop between C# and C++, I recommend COM as it doesn't require you to write any wrappers (which get really messy in more complicated scenarios), although of course it requires you to modify the existing C++ code.
Related
My project requires me to use C# to provide a user interface to C++. One of the C++ function I call does a bunch of work and provides periodic progress updates through another "object." Here's a example of what I mean.
C++
class AppDelegate : public ProgressDelegate
{
void AppDelegate::UpdateStatusText(const char* text)
{
// Go() will end up calling me at some point.
OutputDebugString(text);
}
void AppDelegate::ShowMessage(const char* text)
{
// Go() will end up calling me at some point.
OutputDebugString(text);
}
};
int CppWrapper::Go()
{
return cppInstance->Go()
}
CSharp
void UpdateStatusText(String text)
{
//update UI
}
void ShowMessage(String text)
{
//update UI
}
What I want to do is take updateStatusText and ShowMessage and pass the text over to C# to update my UI. My question is how do I expose the appropriate C# methods so that they can be called by my C++ code? Note that modifying Go is not an option for me.
Maybe this example can help you:
Write a Managed DLL
To create a simple managed DLL that has a public method to add two numbers and return the result, follow these steps:
Start Microsoft Visual Studio .NET or Microsoft Visual Studio 2005.
On the File menu, point to New, and then click Project. The New Project dialog box opens.
Under Project Types, click Visual C# Projects.
Note In Visual Studio 2005, click Visual C# under Project Types.
Under Templates, click Class Library.
In the Name text box, type sManagedDLL, and then click OK.
Open the Class1.cs file in Code view.
To declare a public interface that has a method to add two numbers, add the following code to the Class1.cs file:
// Interface declaration.
public interface ICalculator
{
int Add(int Number1, int Number2);
};
To implement this public interface in a class, add the following code to the Class1.cs file:
// Interface implementation.
public class ManagedClass:ICalculator
{
public int Add(int Number1,int Number2)
{
return Number1+Number2;
}
}
Register the Managed DLL for Use with COM or with Native C++
To use the managed DLL with COM or with native C++, you must register the assembly information of your DLL in the Windows registry. To do this, follow these steps:
Call the Managed DLL from Native C++ Code
// Import the type library.
#import "..\ManagedDLL\bin\Debug\ManagedDLL.tlb" raw_interfaces_only
Change the path of the type library if the path on your computer differs from this path.
To declare the namespace to use, add the following code to the CPPClient.cpp file:
using namespace ManagedDLL;
Complete Code Listing
//Managed DLL
// Class1.cs
// A simple managed DLL that contains a method to add two numbers.
using System;
namespace ManagedDLL
{
// Interface declaration.
public interface ICalculator
{
int Add(int Number1, int Number2);
};
// Interface implementation.
public class ManagedClass:ICalculator
{
public int Add(int Number1,int Number2)
{
return Number1+Number2;
}
}
}
//C++ Client
// CPPClient.cpp: Defines the entry point for the console application.
// C++ client that calls a managed DLL.
#include "stdafx.h"
#include "tchar.h"
// Import the type library.
#import "..\ManagedDLL\bin\Debug\ManagedDLL.tlb" raw_interfaces_only
using namespace ManagedDLL;
int _tmain(int argc, _TCHAR* argv[])
{
// Initialize COM.
HRESULT hr = CoInitialize(NULL);
// Create the interface pointer.
ICalculatorPtr pICalc(__uuidof(ManagedClass));
long lResult = 0;
// Call the Add method.
pICalc->Add(5, 10, &lResult);
wprintf(L"The result is %d\n", lResult);
// Uninitialize COM.
CoUninitialize();
return 0;
}
Reference:
How to call a managed DLL from native Visual C++ code in Visual Studio.NET or in Visual Studio 2005
Alternatively, what I used to do (before I switched to using P/Invoke method to call from C# to C++) was to have 3 projects (as StraightLine has mentioned) but I'd have C#, Managed C++, and Native C++, and have the Managed C++ be my bridge/proxy to talk between the two (Native C++ and C#). It made it more easier to work on my Native C++ side that way. One caution is that some of the STL (mostly containers) are not supported by managed or sometimes, behaviors of std::string (Managed C++ version) would cause exceptions when used in Native C++ std::string, so do pay attention to which STL libraries are Managed C++ supported.
Also, as StraightLine has mentioned, the bridged code (in my case, Manaaged C++) would have to have a wrapper which will marshal from Managed to Native and vice versa (i.e. your "const char*" to System.String, if your char is 8-bits, etc)
You would have to build relevant C# code into an assembly, then reference that assembly inside C++ CLI project. Inside your C++ CLI wrapper, you will make calls to functions exposed through this C# assembly, also you will make calls into native C++ code.
The C++ CLI project can contain native C++ code, just make sure that the CLR switch is not enabled for native files. So, you would have 3 projects -
C# project for GUI which will invoke main. Also references the assembly used to expose C# functions to be called via C++ interop.
C# assembly that exposes certain managed functions (thus callable from C++ CLI)
C++ CLI project which will wrap and also contain native code.
I'm working on some code that is not mine, and it passes an argument in c++ to a (managed COM) c# method that doesn't have any parameters. The code works fine, but I don't know why.
Can someone explain what's going on or point me to the c++ constructs that make it possible?
Here's the code:
//---------- C++ ----------
#import "wrapper.tlb" named_guids raw_interfaces_only
BSTR b;
m_wrapper->getException(&b);
CW2A conv(b);
std::string s(conv);
if (! s.empty() ) {
//Perform exception processing
{
//---------- C# Managed COM ----------
public class wrapper : Iwrapper
{
private exceptionStr = String.Empty; // 'exceptionStr' set elsewhere in C# for an eventual pull by C++
public string getException()
{
return exceptionStr;
}
//... other C# methods that may set 'exceptionStr'
}
The COM standard interface does not allow return parametres, since any function returns an HRESULT. So what appear to be as a return value in the COM object in C# is marshalled as a reference in the C++ side.
Title explains. I have native C++ dlls that I'm writing C++/CLI wrappers for, which will in turn will be imported in C# as reference.
The problem is that in C# I don't see the classes I have in wrapper (imported from DLL).
What keywords should I use and HOW to re-declare my native C++ objects to become visible in C#?
Ok, tutorial. You have a C++ class NativeClass that you want to expose to C#.
class NativeClass {
public:
void Method();
};
1) Create a C++/CLI project. Link to your C++ library and headers.
2) Create a wrapper class that exposes the methods you want. Example:
#include "NativeClass.h"
public ref class NativeClassWrapper {
NativeClass* m_nativeClass;
public:
NativeClassWrapper() { m_nativeClass = new NativeClass(); }
~NativeClassWrapper() { this->!NativeClassWrapper(); }
!NativeClassWrapper() { delete m_nativeClass; }
void Method() {
m_nativeClass->Method();
}
};
3) Add a reference to your C++/CLI project in your C# project.
4) Use the wrapper type within a using statement:
using (var nativeObject = new NativeClassWrapper()) {
nativeObject.Method();
}
The using statement ensures Dispose() is called, which immediately runs the destructor and destroys the native object. You will otherwise have memory leaks and probably will die horribly (not you, the program). Note : The Dispose() method is magically created for you.
I'm trying to avoid COM. I'm designing a mixture C# and C++ controls on a C++ exe.
One method I came up with is PInvoking my C++ exe from C#, and sending windows messages to the C# windows. However the amount of methods I call on the controls base class is too long to justify windows messages.
So, if it's possible to export a whole C# interface to a C++ exe, that would be way easier.
I want to avoid COM because I may have to support windows 2000, and doing COM without relying on the manifest would be a deployment hassle on a software package that currently doesn't set much in the registry.
You could write a C wrapper for each of your C++ controls, and PInvoke from C#.
For example this C++ class:
class Example
{
public:
int MyMethod(int param);
}
and in a extern "C" block in your c++ exe:
void * CreateExample() { return new Example(); }
int Example_MyMethod(void * handle, int param) { reinterpret_cast<Example*>(handle)->MyMethod(param)); }
and in C#:
public class Example
{
private IntPtr handle;
public Example()
{
handle = _CreateExample();
}
public int MyMethod(int param)
{
return _MyMethod(param);
}
[DllImport("yourdll.exe")]
private static extern IntPtr _CreateExample();
[DllImport("yourdll.exe")]
private static extern int _MyMethod(IntPtr handle, int param);
}
I use C++/CLI with VS 2010 to do this. You can expose a DLL C interface that can be consumed in the usual way, the implementation would just marshal data from that interface to your C# assembly.
Related question I think Calling C# from C++, Reverse P/Invoke, Mixed Mode DLLs and C++/CLI
I have been tasked with maintaining a legacy unmanaged c++ system. I do not have access to the source of the entire system but I do have the source to a number of extension dlls that, when included in the same directory as the core system, will be loaded instead of the built in defaults.
I have used the extensions in the past for small changes without problems. My issue now, however, is that I'm being asked to overhaul one of the extension dlls with a substantial amount of extra functionality. Creating this extra functionality in C# is going to be significantly faster (time-to-develop) and more maintainable (our team is primarily composed of C# devs).
The extension dll only has two functions that get called by the core system. The two functions take a bool, int, uint, RECT, Point, CString and return void. Some of the parameters they accept are const.
I'm really keen to find a solid way to bridge these extension functions to C# (.NET 4). So far I've put considerable effort into researching COM Visible, Regasm, c++ mixed mode and interop wrapping libraries. I've also lost a considerable amount of time on proof of concept projects during this research and so far I do not have a working 'bridge'.
What is the most pain free method to get this up and running?
I'm under considerably more pressure on this project than normal - I'm literally starting the C# now and assuming I will get this working somehow.
Really appreciate help and feedback.
Here is the .h and .def files:
modeldll.h
#ifndef INC_MODELDLL_H
#define INC_MODELDLL_H
#ifdef MODELDLL_EXPORTS
#define MODELDLL_API __declspec(dllexport)
#else
#define MODELDLL_API __declspec(dllimport)
#endif
typedef int (*model_updatemodel_t)(const bool update_model, const HWND hwnd, const RECT rect, const POINT next_point, const CString title);
MODELDLL_API int UpdateModel(const bool update_model, const HWND hwnd, const RECT rect, const POINT next_point, const CString title);
typedef int (*model_updatemodelpoint_t)(const bool update_model, const HWND hwnd, const RECT rect, UINT update, const POINT next_point);
MODELDLL_API int UpdateModelPoint(const bool update_model, const HWND hwnd, const RECT rect, UINT update, const POINT next_point);
typedef void (*model_process_message_t)(const char *message, const void *param);
MODELDLL_API void ProcessMessage(const char *message, const void *param);
#endif // INC_MODELDLL_H
modeldll.def:
LIBRARY model.dll
EXPORTS
ProcessMessage #1
UpdateModel #2
UpdateModelPoint #3
I've investigated this topic couple of years ago: I want to use log4net and Npgsql libraries from native code that compiles even withour /clr key.
The main idea behind this technique described by Paul DiLascia in his two remarkable articles:
Managed Code in Visual Studio 2005
Use Our ManWrap Library to Get the Best of .NET in Native C++ Code
For example, here some code snippets that uses log4net library from native code (this code resides in simple non-managed dll, but you should compile this with /clr, but it's not nessary to compile with /clr key code that would use this dll from native code):
// Log4NetWrapper.h
#pragma once
using namespace System;
//facade for log4net library (you may create something like this too)
ref class Log4NetWrapper
{
public:
//I intentionally remove additional methods, because
//I'm trying to show the main principle
static void ReportDebugMessage(char* msg);
private:
static property log4net::ILog^ Logger
{
log4net::ILog^ get();
}
static Object^ syncObject_ = gcnew Object();
static String^ loggerName_ = "";
};
//C-interface that could be accessed from native code
extern "C"
{
_declspec(dllexport) void ReportDebugMessage(char* msg)
{
Log4NetWrapper::ReportDebugMessage(msg);
}
}
// This is the main DLL file.
#include "stdafx.h"
#include "Log4NetWrapper.h"
void Log4NetWrapper::ReportDebugMessage(char* msg)
{
String^ data = gcnew String(msg);
Logger->Debug(data);
}
log4net::ILog^ Log4NetWrapper::Logger::get()
{
if ( loggerName_ == nullptr )
return log4net::LogManager::GetLogger("");
return log4net::LogManager::GetLogger(loggerName_);
}
Compile this code as native dll, than add this dll to your native project, add something like this to that project:
#pragma once
#pragma comment(lib, "Log4NetWrapper")
extern "C"
{
_declspec(dllimport) void ReportDebugMessage(char* msg);
}
And use ReportDebugMessage to access managed code from native code.
Without further information there's not much to go on but I would suggest that you have the following.
Extension Dll (unmanaged code) -> Managed C++ (wrapper) -> C# dll
The first jump is explained in this example:
http://www.codeproject.com/KB/mcpp/cpptomancpp.aspx
You can then load the c# assembly from the managed c++ fairly easily using
using namespace YourNameSpace; // the namespace of the c# routines
In time you may be able to merge the first two.
As Preet suggested, this can be done using a Managed C++ wrapper that will do the bridging you need.
This article explains the entire process:
http://www.codeproject.com/KB/mcpp/unmanaged_to_managed.aspx
I've actually done these sort of things quite a lot several years ago, and all direction work pretty well - C# calling C++ code, C++ code calling C# (via a Managed C++ proxy) and C# passing delegate to a C++ code treating them as function pointers and calling them. I've had some example projects for this, I'll try and find them.