问题

以下是要翻译的内容：

我有一段 `C++` 代码，我想将其打包成一个 dll 并在 `C#` 代码中使用。我创建了 dll，但当我加载它时，出现了 `System.AccessViolationException` 错误。（首先，dll 无法加载，然后开始加载后出现了访问冲突错误）。

我在 `C++` 中编写了一段代码，我的团队其他成员希望将其纳入到一个 Windows Forms 应用程序中，我认为这是学习关于 `C++` dll 项目并将其纳入到 C#/Windows Forms 的机会。我在 YouTube 上找到了一个教程，然后为我的 dll 编写了以下代码：

extern "C" _declspec(dllexport) Communication* CreateCommunicationObject(const char* ip, unsigned int p_out, unsigned int p_in)
{
return &Communication::Communication(ip, p_out, p_in);
}

extern "C" _declspec(dllexport) st_rtioout getReceivedData(Communication *comm)
{
return comm->getData();
}

extern "C" _declspec(dllexport) void sendNewData(Communication *comm, st_rtioin *data)
{
return comm->sendData(*data);
}

extern "C" _declspec(dllexport) char* getReceptionStatus(Communication *comm)
{
return comm->getReceptionStatus();
}

extern "C" _declspec(dllexport) char* getSendingStatus(Communication *comm)
{
return comm->getSendingStatus();
}

dll 文件已构建，然后我转到 C#，尝试将 dll 导入为窗体应用程序的引用，但出现错误：“无法添加对 project2.dll 的引用。请确保文件可访问并且是有效的程序集或 com 组件”，在搜索一段时间后，我找到了这个[问题](https://stackoverflow.com/questions/8366590/how-to-create-dll-in-c-for-using-in-c-sharp)。然后我在 C# 应用程序中尝试了以下代码：

[DllImport("Project2.dll", EntryPoint = "CreateCommunicationObject", CallingConvention = CallingConvention.StdCall)]
static extern IntPtr CreateCommunicationObject(string ip, int port_out, int port_in);

[DllImport("Project2.dll", EntryPoint = "getReceivedData", CallingConvention = CallingConvention.StdCall)]
static extern st_rtioout getReceivedData(IntPtr ptr);

[DllImport("Project2.dll", EntryPoint = "sendNewData", CallingConvention = CallingConvention.StdCall)]
static extern void sendNewData(IntPtr ptr, st_rtioin sendingdata);

[DllImport("Project2.dll", EntryPoint = "getReceptionStatus", CallingConvention = CallingConvention.StdCall)]
static extern string getReceptionStatus(IntPtr ptr);

[DllImport("Project2.dll", EntryPoint = "getSendingStatus", CallingConvention = CallingConvention.StdCall)]
static extern string getSendingStatus(IntPtr ptr);

但现在在调用类的构造函数 (`createCommunicationObject`) 时出现错误 `System.AccessViolationException`（尝试读取或写入受保护的内存。这通常表明其他内存已损坏）。我做错了什么，如何纠正它？提前感谢您。（我使用的是 VS2013）

编辑：
经过查看评论和答案后，我尝试了你们建议的所有方法，但仍然出现相同的错误。新的 `C++` 代码如下：

extern "C" _declspec(dllexport) void Initialize(std::string ip, unsigned int p_out, unsigned int p_in)
{
const char* ipaddress = ip.c_str();
Communication comms = Communication(ipaddress, p_out, p_in);
Comms = &comms;
}

extern "C" _declspec(dllexport) st_rtioout getReceivedData()
{
return Comms->getData();
}

extern "C" _declspec(dllexport) void sendNewData(st_rtioin data)
{
Comms->sendData(data);
}

extern "C" _declspec(dllexport) std::string getReceptionStatus()
{
std::string str = Comms->getReceptionStatus();
return str;
}

extern "C" _declspec(dllexport) std::string getSendingStatus()
{
std::string str = Comms->getSendingStatus();
return str;
}

和新的 `C#` 代码：

[DllImport("Project2.dll", EntryPoint = "Initialize", CallingConvention = CallingConvention.Cdecl)]
static extern void Initialize(string ip, int port_out, int port_in);

[DllImport("Project2.dll", EntryPoint = "getReceivedData", CallingConvention = CallingConvention.Cdecl)]
static extern st_rtioout getReceivedData();

[DllImport("Project2.dll", EntryPoint = "sendNewData", CallingConvention = CallingConvention.Cdecl)]
static extern void sendNewData(st_rtioin sendingdata);

[DllImport("Project2.dll", EntryPoint = "getReceptionStatus", CallingConvention = CallingConvention.Cdecl)]
static extern string getReceptionStatus();

[DllImport("Project2.dll", EntryPoint = "getSendingStatus", CallingConvention = CallingConvention.Cdecl)]
static extern string getSendingStatus();

<details>
<summary>英文:</summary>

I have code in `C++` that I want to package as a dll and use in `C#` code. I made the dll, but when I am loading it, I am getting `System.AccessViolationException`. (First, the dll wouldn&#39;t load and after it has started loading, Access Violation has started to appear).

I wrote a piece of code in `C++` that other members of my team want to incorporate into a windows forms application, I saw this as an opportunity to learn about `C++` dll projects and incorporating them into C#/Windows Forms. I followed a tutorial on youtube and came up with this code for my dll:

extern "C" _declspec(dllexport) Communication* CreateCommunicationObject(const char* ip, unsigned int p_out, unsigned int p_in)
{
return &Communication::Communication(ip, p_out, p_in);
}

extern "C" _declspec(dllexport) st_rtioout getReceivedData(Communication *comm)
{
return comm->getData();
}

extern "C" _declspec(dllexport) void sendNewData(Communication *comm, st_rtioin *data)
{
return comm->sendData(*data);
}

extern "C" _declspec(dllexport) char* getReceptionStatus(Communication *comm)
{
return comm->getReceptionStatus();
}

extern "C" _declspec(dllexport) char* getSendingStatus(Communication *comm)
{
return comm->getSendingStatus();
}

The dll file was built and then I came into C#, I tried importing the dll as a reference in the Forms application but got an error "a reference to project2.dll could not be added. please make sure that the file is accessible and is a valid assembly or com component", after searching for a while, I came across this [question](https://stackoverflow.com/questions/8366590/how-to-create-dll-in-c-for-using-in-c-sharp). I then tried this in the C# application:

    [DllImport("Project2.dll", EntryPoint = "CreateCommunicationObject", CallingConvention = CallingConvention.StdCall)]
    static extern IntPtr CreateCommunicationObject(string ip, int port_out, int port_in);

    [DllImport("Project2.dll", EntryPoint = "getReceivedData", CallingConvention = CallingConvention.StdCall)]
    static extern st_rtioout getReceivedData(IntPtr ptr);

    [DllImport("Project2.dll", EntryPoint = "sendNewData", CallingConvention = CallingConvention.StdCall)]
    static extern void sendNewData(IntPtr ptr, st_rtioin sendingdata);

    [DllImport("Project2.dll", EntryPoint = "getReceptionStatus", CallingConvention = CallingConvention.StdCall)]
    static extern string getReceptionStatus(IntPtr ptr);

    [DllImport("Project2.dll", EntryPoint = "getSendingStatus", CallingConvention = CallingConvention.StdCall)]
    static extern string getSendingStatus(IntPtr ptr);

But now I am getting an error `'System.AccessViolationException'(Attempted to read or write protected memory. This is often an indication that other memory is corrupt.)` where I am calling the constructor of the class (`createCommunicationObject`). 

What am I doing wrong and how can I rectify it? thanks in advance. (I am using VS2013)



Edit:
After going through the comments and the answers, I tried all that you people suggested, but am still getting the same error. The New `C++` code is:

extern "C" _declspec(dllexport) void Initialize(std::string ip, unsigned int p_out, unsigned int p_in)
{
const char* ipaddress = ip.c_str();
Communication comms = Communication(ipaddress, p_out, p_in);
Comms = &comms;
}

extern "C" _declspec(dllexport) st_rtioout getReceivedData()
{
return Comms->getData();
}

extern "C" _declspec(dllexport) void sendNewData(st_rtioin data)
{
Comms->sendData(data);
}

extern "C" _declspec(dllexport) std::string getReceptionStatus()
{
std::string str = Comms->getReceptionStatus();
return str;
}

extern "C" _declspec(dllexport) std::string getSendingStatus()
{
std::string str = Comms->getSendingStatus();
return str;
}

and the new `C#` code is:

    [DllImport("Project2.dll", EntryPoint = "Initialize", CallingConvention = CallingConvention.Cdecl)]
        static extern void Initialize(string ip, int port_out, int port_in);

        [DllImport("Project2.dll", EntryPoint = "getReceivedData", CallingConvention = CallingConvention.Cdecl)]
        static extern st_rtioout getReceivedData();

        [DllImport("Project2.dll", EntryPoint = "sendNewData", CallingConvention = CallingConvention.Cdecl)]
        static extern void sendNewData(st_rtioin sendingdata);

        [DllImport("Project2.dll", EntryPoint = "getReceptionStatus", CallingConvention = CallingConvention.Cdecl)]
        static extern string getReceptionStatus();

        [DllImport("Project2.dll", EntryPoint = "getSendingStatus", CallingConvention = CallingConvention.Cdecl)]
        static extern string getSendingStatus();



</details>


# 答案1
**得分**: 2

你在这里返回了一个指向堆栈变量的指针：
```c++
extern "C" _declspec(dllexport) Communication* CreateCommunicationObject(const char* ip, unsigned int p_out, unsigned int p_in)
{
    return &Communication::Communication(ip, p_out, p_in);
}

这会导致崩溃，因为堆栈变量在函数结束后不会继续存在。如果查看编译器消息，编译器可能会警告你。

你想要做的是在堆上分配对象：

extern "C" _declspec(dllexport) Communication* CreateCommunicationObject(const char* ip, unsigned int p_out, unsigned int p_in)
{
    return new Communication::Communication(ip, p_out, p_in);
}

并且一旦不再需要对象，你可能还需要一个析构函数方法：

extern "C" _declspec(dllexport) void DestroyCommunicationObject(Communication* object)
{
    delete object;
}

这可能会使你在使用 P/Invoke 时正常工作。

在验证这是否有效后，在C#中的最佳实践是创建一个实现 IDisposable 的包装类。

extern "C" _declspec(dllexport) Communication* CreateCommunicationObject(const char* ip, unsigned int p_out, unsigned int p_in)
{
    return &Communication::Communication(ip, p_out, p_in);
}

extern "C" _declspec(dllexport) Communication* CreateCommunicationObject(const char* ip, unsigned int p_out, unsigned int p_in)
{
    return new Communication::Communication(ip, p_out, p_in);
}

extern "C" _declspec(dllexport) void DestroyCommunicationObject(Communication* object)
{
    delete object;
}