相关疑难解决方法(0)

如果struct包含DateTime字段,为什么LayoutKind.Sequential的工作方式不同？

请考虑以下代码(必须使用"unsafe"启用的编译器应用程序):

using System;
using System.Runtime.InteropServices;

namespace ConsoleApplication3
{
    static class Program
    {
        static void Main()
        {
            Inner test = new Inner();

            unsafe
            {
                Console.WriteLine("Address of struct   = " + ((int)&test).ToString("X"));
                Console.WriteLine("Address of First    = " + ((int)&test.First).ToString("X"));
                Console.WriteLine("Address of NotFirst = " + ((int)&test.NotFirst).ToString("X"));
            }
        }
    }

    [StructLayout(LayoutKind.Sequential)]
    public struct Inner
    {
        public byte First;
        public double NotFirst;
        public DateTime WTF;
    }
}

现在如果我运行上面的代码,我得到类似于以下的输出:

struct = 40F2CC的
地址First = 40F2D4的
地址NotFirst的地址= 40F2CC

注意,First的地址与struct的地址不同; 然而,NotFirst的地址是一样的结构的地址.

现在注释掉结构中的"DateTime WTF"字段,然后再次运行它.这一次,我得到的输出类似于:

struct …

当我用Google搜索时,我看到帖子说传递C#class与ref struct使用PInvoke时传递给C API 相同(这里是一个帖子C#PInvoke struct vs class access violation).

但是,在运行示例时,我看到的行为与预期不同.在ref struct"类"中没有作为真正指针的地方

C代码:

//PInvokeProvider.h
#include "stdafx.h" 
typedef struct Animal_s
{
    char Name[10000];
} Animal;

extern "C" void __declspec(dllexport) ChangeName(Animal* pAnimal);


//PInvokeProvider.cpp    
#include "stdafx.h"
#include <stdio.h>
#include "PInvokeProvider.h"

extern "C" {
    void ChangeName(Animal* pAnimal)
    {
        printf("Entered C++\n");
        printf("Recieved animal : %s\n", pAnimal->Name);
        printf("This function will change the first letter of animal to 'A'\n");
        pAnimal->Name[0] = 'A';
        printf("Animal changed to : %s\n", pAnimal->Name);
        printf("Leaving C++\n"); …

我遇到了一个奇怪的场景,它在C#/ .NET中包含了包含数组的联合.考虑以下程序:

namespace Marshal
{
    class Program
    {
        [StructLayout(LayoutKind.Sequential, Pack = 1)]
        struct InnerType
        {
            byte Foo;
            //[MarshalAs(UnmanagedType.ByValArray, ArraySubType = UnmanagedType.Struct, SizeConst = 1)]
            //byte[] Bar;
        }


        [StructLayout(LayoutKind.Explicit, Pack = 1)]
        struct UnionType
        {
            [FieldOffset(0)]
            InnerType UnionMember1;

            [FieldOffset(0)]
            [MarshalAs(UnmanagedType.ByValArray, ArraySubType = UnmanagedType.Struct, SizeConst = 1)]
            byte[] UnionMember2;
        }

        static void Main(string[] args)
        {
            Console.WriteLine(@"SizeOf UnionType: {0}", System.Runtime.InteropServices.Marshal.SizeOf(typeof(UnionType)));
        }
    }
}

如果您运行此程序,您将获得以下异常:

Could not load type 'UnionType' from assembly 'Marshal, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null' because it contains an object field at offset …