我对DLL的几个问题。我尝试了很多，但我不能获得完整的信息。大多数的例子是在C＃等。
I have a few questions about DLL's. I tried a lot but I can not get the complete picture. Most examples are in C# etc.
使用向导在VS2005我创建了一个非托管的MFC规则DLL（一定是因为剩余的code MFC）。然后我试图导入在托管的.NET C ++应用程序VS2005。见下面code。
With the wizard in VS2005 I created a unmanaged MFC regular DLL (must be MFC because of remaining code). Then I tried to import it in a VS2005 managed .NET C++ application. See code below.
mfc_main.h：
mfc_main.h:
//---------------------------------------------------------
// mfc_main.h : main header file for the mfc_main DLL
//---------------------------------------------------------
#pragma once
#ifndef __AFXWIN_H__
#error "include 'stdafx.h' before including this file for PCH"
#endif
#include "resource.h" // main symbols
class __declspec(dllexport) Cmfc_mainApp : public CWinApp
{
public:
Cmfc_mainApp();
// Overrides
public:
virtual BOOL InitInstance();
int SayHello(int j);
int init;
DECLARE_MESSAGE_MAP()
};
mfc_main.cpp：
mfc_main.cpp:
//----------------------------------------------------------------
// mfc_main.cpp : Defines the initialization routines for the DLL.
//----------------------------------------------------------------
#include "stdafx.h"
#include "mfc_main.h"
#ifdef _DEBUG
#define new DEBUG_NEW
#endif
BEGIN_MESSAGE_MAP(Cmfc_mainApp, CWinApp)
END_MESSAGE_MAP()
Cmfc_mainApp::Cmfc_mainApp()
{
}
Cmfc_mainApp theApp;
BOOL Cmfc_mainApp::InitInstance()
{
CWinApp::InitInstance();
return TRUE;
}
int Cmfc_mainApp::SayHello(int j)
{
init = 12; // Comment this out the application works !!!!
return j * 6;
};
在应用程序
[DllImport("mfc_main.dll",
EntryPoint = "?SayHello@Cmfc_mainApp@@QAEHH@Z",
ExactSpelling = true)]
static int SayHello(int a);
......
private: System::Void button_Click(System::Object^ sender, System::EventArgs^ e)
{
int retval = SayHello(2);
}
我的问题是：
My questions are:
1 - 为什么不工作在init = 12在功能的SayHello和应用程序崩溃（错误：试图读取或写入受保护的内存）
1 - Why is it working without the init = 12 in the function SayHello and with the application crashes (error: Attempted to read or write protected memory)?
2 - 在这种情况下的InitInstance（）执行的，虽然我不把它（和为什么没有ExitInstance中）
2 - Is in this case the InitInstance() executed although I don't call it (and why is there no ExitInstance)?
3 - ？为什么我看一些例子使用的DllImport时给予入口点和一些不
3 - Why do I see some examples giving the EntryPoint when using DLLImport and some don't?
4 - ？我可以给一个委托作为参数，在MFC C ++ DLL，而不是一个正常的函数指针的函数，来创建一个回调
4 - Can I give a delegate as parameter to a function in a MFC C++ DLL instead of a normal function pointer, to create a callback?
推荐答案
方法不能被P /调用。如果你要导出的非托管的DLL一类管理的世界中使用，你必须将其压平，如：
Methods cannot be P/Invoked. If you want to export a class from unmanaged DLL to be used in managed world, you have to flatten it, eg.
创建一个构造函数，它看起来像：
Create a constructor function, which looks like:
__declspec(dllexport) void * __stdcall MyClass_Create()
{
return new MyClass();
}
创建一个析构函数，它是这样的：
Create a destructor function, which looks like:
__declspec(dllexport) void * __stdcall MyClass_Destroy(MyClass * instance)
{
delete instance;
}
拼合方法调用。让我们假设，你有下面的方法在您的类：
Flatten method calls. Let's suppose, that you have the following method in your class:
int MyClass::MyMethod(int i, double j) { ... }
然后，你必须创建如下功能：
Then you have to create a following function:
__declspec(dllexport) int __stdcall MyClass_MyMethod(MyClass * instance, int i, double j)
{
return instance->MyMethod(i, j);
}
prepare P / C＃中调用外部方法（你已经知道如何做到这一点，所以我会忽略这些）
Prepare P/Invoked external methods in C# (You already know how to do it, so I'll omit these)
创建类的实例：
IntPtr instance = MyClass_Create();
然后调用它的方法：
Then call its method:
int i = MyClass_MyMethod(instance, 4, 2.0);
最后，破坏类：
Finally, destroy the class:
MyClass_Destroy(instance);
不要忘记添加一些错误检查 - 我忽略它使例子清楚
Don't forget to add some error checking - I omitted it to keep the example clear.
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