.NET通过P/Invoke调用C API触发System.AccessViolationException问题

System.AccessViolationException: Attempted to read or write protected memory. This is often an indication that other memory is corrupt.

调用一个void类型的C API时触发上述异常，该API的输入是仅包含基础类型的结构体。目前已有多个使用更复杂结构体的API方法可正常运行，且异常在Debug和Release模式下均会出现。

当前发现特殊现象：在C/C++和C#两端的结构体中同时取消注释int placeholder字段后，代码即可正常运行，且P/Invoke传递的数据完全正确。另外在另一个包含int类型枚举和int字段的结构体中也遇到相同情况，必须添加第三个int成员才能避免触发异常。

环境配置 #

• VS 17 2022
• C++ 20
• .NET Framework 4.7.2

C/C++端代码 #

typedef struct
{
    float visibility; //[m] Visibility range
    float thickness;  //[m] Thickness of the fog layer
    // int placeholder;
} Fog;

/// @brief set fog data to be forwarded to the IG
/// @param fog \ref Fuze::Interfaces::Fog with fog data
/// @param regionId the id of the region to be updated
extern "C" __declspec(dllexport) void SetFogData(const Fog* fog, int regionId);

///interface.cpp
#include "Interface.h"
#include <iostream>

void SetFogData(const Fog* fog, int regionId)
{
    std::cout << "\n\nForwarding fog data to plugins\n";
    std::cout << "Fog data: " << fog->thickness << " " << fog->visibility << std::endl;
}

C#端代码 #

using System.Runtime.InteropServices;

namespace Fuze
{
    [StructLayout(LayoutKind.Sequential)]
    public struct Fog
    {
        public float Visibility; // [m] Visibility range
        public float Thickness;  // [m] Thickness of the fog
        // int placeholder;
    }
    static public class API
    {
        private const string dllPath = "Fuze_API.dll";

        [DllImport(dllPath, CallingConvention = CallingConvention.Cdecl)]
        public static extern void SetFogData(Fog fog, int regionId);

    }
}

// main.cs

using static Fuze.API;

class FakeClientDotNet
{
    static void Main(string[] args)
    {
        Fuze.Fog fog = new Fuze.Fog();
        fog.Thickness = 50.0f;
        fog.Visibility = 250.0f;
        SetFogData(fog, 0);
        
        System.Console.WriteLine("\nCompleted\n");
    }
}

内容的提问来源于stack exchange，提问作者user19905921