C#中的C ++联合 - 奇怪的行为

时间:2016-06-04 00:03:57

标签: c# c++ pinvoke

我正在尝试使用C#中的VHD API创建一些vhd / vhdx文件。

有一个看起来像这样的C ++联盟:

typedef struct _CREATE_VIRTUAL_DISK_PARAMETERS
{
    CREATE_VIRTUAL_DISK_VERSION Version;

    union
    {
        struct
        {
            GUID                  UniqueId;
            ULONGLONG             MaximumSize;
            ULONG                 BlockSizeInBytes;
            ULONG                 SectorSizeInBytes;
            PCWSTR                ParentPath;
            PCWSTR                SourcePath;
        } Version1;

        struct
        {
            GUID                   UniqueId;
            ULONGLONG              MaximumSize;
            ULONG                  BlockSizeInBytes;
            ULONG                  SectorSizeInBytes;
            ULONG                  PhysicalSectorSizeInBytes;
            PCWSTR                 ParentPath;
            PCWSTR                 SourcePath;
            OPEN_VIRTUAL_DISK_FLAG OpenFlags;
            VIRTUAL_STORAGE_TYPE   ParentVirtualStorageType;
            VIRTUAL_STORAGE_TYPE   SourceVirtualStorageType;
            GUID                   ResiliencyGuid;
        } Version2;

        struct
        {
            GUID                   UniqueId;
            ULONGLONG              MaximumSize;
            ULONG                  BlockSizeInBytes;
            ULONG                  SectorSizeInBytes;
            ULONG                  PhysicalSectorSizeInBytes;
            PCWSTR                 ParentPath;
            PCWSTR                 SourcePath;
            OPEN_VIRTUAL_DISK_FLAG OpenFlags;
            VIRTUAL_STORAGE_TYPE   ParentVirtualStorageType;
            VIRTUAL_STORAGE_TYPE   SourceVirtualStorageType;
            GUID                   ResiliencyGuid;
            PCWSTR                 SourceLimitPath;
            VIRTUAL_STORAGE_TYPE   BackingStorageType;
        } Version3;
    };
} CREATE_VIRTUAL_DISK_PARAMETERS, *PCREATE_VIRTUAL_DISK_PARAMETERS;

我正在尝试将其转换为C#,但没有太多运气。我根本不对Version3感兴趣,所以我就把它排除在外。

我已经尝试了很多东西,我能做的最好的就是让Version2工作(通过做一些非常奇怪的事情),但我从来没有设法让Version1和Version2同时工作。

到目前为止已经取得了最好结果的解决方案就是这样,但是由于Version1根本不起作用,而Version1中的SectorSizeInBytesulong而不是uint(如果我将它更改为uint,我会破坏版本2,而版本1仍无效!)

[StructLayout(LayoutKind.Explicit, CharSet = CharSet.Unicode)]
public struct CreateVirtualDiskParameters
{
    [FieldOffset(0)] public CreateVirtualDiskParametersVersion1 Version1;

    [FieldOffset(0)] public CreateVirtualDiskParametersVersion2 Version2;
}

[StructLayout(LayoutKind.Sequential, CharSet = CharSet.Unicode)]
public struct CreateVirtualDiskParametersVersion1
{
    public CreateVirtualDiskVersion Version;
    public Guid UniqueId;
    public ulong MaximumSize;
    public uint BlockSizeInBytes;
    public ulong SectorSizeInBytes;
    public string ParentPath;
    public string SourcePath;
}

[StructLayout(LayoutKind.Sequential, CharSet = CharSet.Unicode)]
public struct CreateVirtualDiskParametersVersion2
{
    public CreateVirtualDiskVersion Version;
    public Guid UniqueId;
    public ulong MaximumSize;
    public uint BlockSizeInBytes;
    public uint SectorSizeInBytes;
    public uint PhysicalSectorSizeInBytes;
    public string ParentPath;
    public string SourcePath;
    public OpenVirtualDiskFlags OpenFlags;
    public VirtualStorageType ParentVirtualStorageType;
    public VirtualStorageType SourceVirtualStorageType;
    public Guid ResiliencyGuid;
}

我从理论上知道Version字段应该在Version结构之外设置,我也试过了,但它只是让事情更加有趣......

那么,有人可以建议如何正确地将上述内容翻译成C#,而不需要那样的Version3结构吗?

1 个答案:

答案 0 :(得分:1)

使用Pack = 1StructLayout属性可消除struct成员之间的任何填充。 在TCP连接中,结构通常在没有填充的情况下传递,因此使用该结构的所有程序都可以在内存中对其布局达成一致。

然而,正如@David Heffernan指出的那样,将结构传递给Windows DLL时可能并非如此。我没有测试到CreateVirtualDisk的实际通话,因为它看起来有点冒险,因为之前我还没有使用过这个电话,如果我做了一个,我也不想破坏我的磁盘错误。根据以下引用,看起来默认包装为8个字节(默认为Pack = 0Pack = 8)可能是正确的设置。

请参阅64-bit Windows API struct alignment caused Access Denied error on named pipe

Windows SDK期望打包为8个字节。来自Using the Windows Headers

  

项目应编译为使用默认结构打包,当前为8个字节,因为最大的整数类型是8个字节。这样做可确保头文件中的所有结构类型都编译到应用程序中,并具有Windows API期望的相同对齐。它还确保具有8字节值的结构正确对齐,并且不会在强制数据对齐的处理器上引起对齐错误。

Version移至CreateVirtualDiskParameters的顶部。 然后两个工会跟随。两者都具有相同的偏移量sizeof(CREATE_VIRTUAL_DISK_VERSION)

同样SectorSizeInBytesuint而不是ulong

您可以让编组人员使​​用该属性完成填充string成员的工作,例如

[MarshalAs(UnmanagedType.LPWStr)] public string ParentPath;

或者,您可以在内存中显示它,它是指向Unicode字符串的指针:

public IntPtr ParentPath;

然后用

自己提取字符串
Marshal.PtrToStringAuto(vdp.Version1.ParentPath)

如果您将C#结构传递给外部DLL,请使用非托管字符串填充

vdp.Version1.ParentPath = (IntPtr)Marshal.StringToHGlobalAuto("I am a managed string");

然后在你完成它时释放非托管字符串

Marshal.FreeHGlobal(vdp.Version1.ParentPath);

试试这个。

public enum CREATE_VIRTUAL_DISK_VERSION
{
    CREATE_VIRTUAL_DISK_VERSION_UNSPECIFIED = 0,
    CREATE_VIRTUAL_DISK_VERSION_1 = 1,
    CREATE_VIRTUAL_DISK_VERSION_2 = 2
};
public enum OPEN_VIRTUAL_DISK_FLAG
{
    OPEN_VIRTUAL_DISK_FLAG_NONE = 0x00000000,
    OPEN_VIRTUAL_DISK_FLAG_NO_PARENTS = 0x00000001,
    OPEN_VIRTUAL_DISK_FLAG_BLANK_FILE = 0x00000002,
    OPEN_VIRTUAL_DISK_FLAG_BOOT_DRIVE = 0x00000004,
    OPEN_VIRTUAL_DISK_FLAG_CACHED_IO = 0x00000008,
    OPEN_VIRTUAL_DISK_FLAG_CUSTOM_DIFF_CHAIN = 0x00000010
};

[StructLayout(LayoutKind.Sequential, Pack = 8, CharSet = CharSet.Unicode)]
public struct VIRTUAL_STORAGE_TYPE
{
    uint DeviceId;
    Guid VendorId;
};

[StructLayout(LayoutKind.Explicit, Pack = 8, CharSet = CharSet.Unicode)]
public struct CreateVirtualDiskParameters
{
    [FieldOffset(0)]
    public CREATE_VIRTUAL_DISK_VERSION Version;

    [FieldOffset(8))]
    public CreateVirtualDiskParametersVersion1 Version1;

    [FieldOffset(8))]
    public CreateVirtualDiskParametersVersion2 Version2;
}

[StructLayout(LayoutKind.Sequential, Pack = 8, CharSet = CharSet.Unicode)]
public struct CreateVirtualDiskParametersVersion1
{
    public Guid UniqueId;
    public ulong MaximumSize;
    public uint BlockSizeInBytes;
    public uint SectorSizeInBytes;
    //public IntPtr ParentPath;   // PCWSTR in C++ which is a pointer to a Unicode string
    //public IntPtr SourcePath;   //string
    [MarshalAs(UnmanagedType.LPWStr)] public string ParentPath;
    [MarshalAs(UnmanagedType.LPWStr)] public string SourcePath;
}

[StructLayout(LayoutKind.Sequential, Pack = 8, CharSet = CharSet.Unicode)]
public struct CreateVirtualDiskParametersVersion2
{
    public Guid UniqueId;
    public ulong MaximumSize;
    public uint BlockSizeInBytes;
    public uint SectorSizeInBytes;
    public uint PhysicalSectorSizeInBytes;
    //public IntPtr ParentPath;   //string
    //public IntPtr SourcePath;   //string
    [MarshalAs(UnmanagedType.LPWStr)] public string ParentPath;
    [MarshalAs(UnmanagedType.LPWStr)] public string SourcePath;
    public OPEN_VIRTUAL_DISK_FLAG OpenFlags;
    public VIRTUAL_STORAGE_TYPE ParentVirtualStorageType;
    public VIRTUAL_STORAGE_TYPE SourceVirtualStorageType;
    public Guid ResiliencyGuid;
}