将结构从VC ++返回到C# [英] Returning Struct from VC++ to C#

问题描述

我已经用VC ++编写了一个结构.我已经制作了VC ++代码的dll，并使用PInvoke在C#中调用了该dll.

I have written a structure in VC++. I have made a dll of the VC++ code and calling this dll in C# using PInvoke.

VC ++ dll看起来像这样

The VC++ dll looks like this

#include <windows.h>
#include <stdio.h>
#include <conio.h>
#include <tchar.h>
#include <iostream>
#if defined(_MSC_VER)
#include <windows.h>
#define DLL extern "C" __declspec(dllexport)
#else
#define DLL
#endif


struct SYSTEM_OUTPUT
{
    int status;
};


DLL SYSTEM_OUTPUT* getStatus()
{
    SYSTEM_OUTPUT* output;
    output->status = 7;

    return output;
}

我正在用C#代码从dll调用getStatus()函数，如下所示；

I am calling the getStatus() function from the dll in my C# code, which looks as follows;

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Text;
using System.Windows.Forms;
using System.Runtime.InteropServices;

namespace UsingReturnStructDLL
{
    [StructLayout(LayoutKind.Sequential)]
    public struct SYSTEM_OUTPUT
    {
        [MarshalAs(UnmanagedType.I4)]
        int Status;
    }



public partial class Form1 : Form
{
    public Form1()
    {
        InitializeComponent();
    }

        public SYSTEM_OUTPUT output;

        [DllImport("ReturnStructDLL", EntryPoint = "getStatus")]
        [return: MarshalAs(UnmanagedType.Struct)]
        public extern static SYSTEM_OUTPUT getStatus();



        private void button1_Click(object sender, EventArgs e)
        {
            try
            {
                SYSTEM_OUTPUT output = getStatus();
            }
            catch (AccessViolationException e)
            {
                label1.Text = e.Message;
            }

        }
    }
}

我想在C#代码中检索结构中的值.通过上面的代码设置，我收到以下错误；

I want to retrieve the values in the struct in my C# code. With the above setup of my code, I am getting the following error;

Cannot marshal 'return value': Invalid managed/unmanaged type combination (Int32/UInt32
must be paired with I4, U4, or Error).

有人可以帮我解决这个问题吗?

Can someone please help me with the issue?

谢谢.

推荐答案

首先使您的C ++代码工作.它是已发布的垃圾邮件，您没有初始化指针.它将因AccessViolation而崩溃.

Make your C++ code work first. It is junk as posted, you don't initialize the pointer. It will crash with an AccessViolation.

在C/C ++中，很难正确返回指向结构的指针 ，您的代码客户端将不知道如何释放内存.它也对P/Invoke编组器造成了严重破坏，它将尝试使用CoTaskMemFree()释放指针.在Vista或更高版本上，这是一个恶作剧，在XP上，这是内存泄漏.

Returning pointers to structures is very hard to get right in C/C++ as well, the client of your code won't know how the memory needs to be released. Which plays havoc on the P/Invoke marshaller as well, it is going to try to release the pointer with CoTaskMemFree(). That's a kaboom on Vista and up, a memory leak on XP.

如果让客户端将指向结构的指针作为参数传递，则所有这些问题都会消失:

All of these problems disappear if you let the client pass a pointer to the structure as an argument:

void getStatus(SYSTEM_OUTPUT* buffer)

然后在C#中变为:

[DllImport("mumble.dll")]
private static extern void getStatus(out SYSTEM_OUTPUT buffer);

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