问题描述
我对DLL有一些疑问.我尝试了很多,但无法获得完整的图片.大多数示例都在C#等中.
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VS2005中的向导,我创建了一个非托管的MFC常规DLL(由于存在剩余代码,因此必须为MFC).然后,我尝试将其导入VS2005管理的.NET C ++应用程序中.参见下面的代码.
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;
};
在应用程序中
[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:
1-为什么在函数SayHello中没有init = 12且应用程序崩溃的情况下工作(错误:尝试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,虽然我没有调用InitInstance(),但是否执行了它(为什么没有ExitInstance)?
2 - Is in this case the InitInstance() executed although I don't call it (and why is there no ExitInstance)?
3-为什么在使用DLLImport时会看到一些示例提供EntryPoint,而有些则没有?
3 - Why do I see some examples giving the EntryPoint when using DLLImport and some don't?
4-我可以给MFC C ++ DLL中的函数(而不是普通的函数指针)提供委托作为参数来创建回调吗?
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
无法P/调用方法.如果要从非托管DLL导出类以在托管环境中使用,则必须将其展平,例如.
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,如下所示:
Create a constructor function, which looks like:
__declspec(dllexport) void * __stdcall MyClass_Create()
{
return new MyClass();
}
创建一个析构函数,如下所示:
Create a destructor function, which looks like:
__declspec(dllexport) void * __stdcall MyClass_Destroy(MyClass * instance)
{
delete instance;
}
展平方法调用.假设您的类中具有以下方法:
Flatten method calls. Let's suppose, that you have the following method in your class:
int MyClass::MyMethod(int i, double j) { ... }
然后您必须创建以下功能:
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);
}
在C#中准备P/调用的外部方法(您已经知道该怎么做,因此我将省略它们)
Prepare P/Invoked external methods in C# (You already know how to do it, so I'll omit these)
创建您的类的实例:
IntPtr instance = MyClass_Create();
然后调用其方法:
int i = MyClass_MyMethod(instance, 4, 2.0);
最后,销毁该类:
MyClass_Destroy(instance);
别忘了添加一些错误检查-为了使示例清晰易懂,我省略了它.
Don't forget to add some error checking - I omitted it to keep the example clear.
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