循环通过IntPtr以生成结构数组时出错

Question

我在从另一个struct中的IntPtr构建struct数组时遇到了问题。

这个结构是由我使用的Windows API返回的：

public struct DFS_INFO_9 {
    [MarshalAs(UnmanagedType.LPWStr)]
    public string EntryPath;
    [MarshalAs(UnmanagedType.LPWStr)]
    public string Comment;
    public DFS_VOLUME_STATE State;
    public UInt32 Timeout;
    public Guid Guid;
    public UInt32 PropertyFlags;
    public UInt32 MetadataSize;
    public UInt32 SdLengthReserved;
    public IntPtr pSecurityDescriptor;
    public UInt32 NumberOfStorages;
    public IntPtr Storage;
}

[DllImport("netapi32", CharSet = CharSet.Auto, SetLastError = true)]
public static extern int NetDfsEnum([MarshalAs(UnmanagedType.LPWStr)]string DfsName, int Level, int PrefMaxLen, out IntPtr Buffer, [MarshalAs(UnmanagedType.I4)]out int EntriesRead, [MarshalAs(UnmanagedType.I4)]ref int ResumeHandle);

我正在尝试获取IntPtr Storage引用的DFS_STORAGE_INFO_1数组。

下面是这个结构(如果重要的话)：

public struct DFS_STORAGE_INFO_1 {
    public DFS_STORAGE_STATE State;
    [MarshalAs(UnmanagedType.LPWStr)]
    public string ServerName;
    [MarshalAs(UnmanagedType.LPWStr)]
    public string ShareName;
    public IntPtr TargetPriority;
}

到目前为止，这段代码一直在努力获取只有一个存储的DFS_INFO_9，但在尝试封送数组中的第二个项目时失败了。

DFS_INFO_9 info = GetInfoFromWinApi();
List<DFS_STORAGE_INFO_1> Storages = new List<DFS_STORAGE_INFO_1>();
for (int i = 0; i < info.NumberOfStorages; i++) {
    IntPtr pStorage = new IntPtr(info.Storage.ToInt64() + i * Marshal.SizeOf(typeof(DFS_STORAGE_INFO_1)));
    DFS_STORAGE_INFO_1 storage = (DFS_STORAGE_INFO_1)Marshal.PtrToStructure(pStorage, typeof(DFS_STORAGE_INFO_1));
    Storages.Add(storage);
}

我得到一个FatalExecutionEngineError，它显示错误代码0x0000005 (访问被拒绝)。我假设DFS_STORAGE_INFO_1的大小被错误计算，导致编组尝试访问分配给数组的内存之外的内存。但这是在i = 1上发生的，当时可能有7个存储空间需要通过。也许我的想法有缺陷，但我不知道如何纠正这一点。

Answer 1

DFS_STORAGE_INFO_1的实际定义如下：

public struct DFS_STORAGE_INFO_1 {
    public DFS_STORAGE_STATE State;
    [MarshalAs(UnmanagedType.LPWStr)]
    public string ServerName;
    [MarshalAs(UnmanagedType.LPWStr)]
    public string ShareName;
    DFS_TARGET_PRIORITY TargetPriority;
}

TargetPriority是一种结构，定义了here

public struct DFS_TARGET_PRIORITY {
    public DFS_TARGET_PRIORITY_CLASS TargetPriorityClass;
    public UInt16 TargetPriorityRank;
    public UInt16 Reserved;
}

public enum DFS_TARGET_PRIORITY_CLASS {
    DfsInvalidPriorityClass = -1,
    DfsSiteCostNormalPriorityClass = 0,
    DfsGlobalHighPriorityClass = 1,
    DfsSiteCostHighPriorityClass = 2,
    DfsSiteCostLowPriorityClass = 3,
    DfsGlobalLowPriorityClass = 4
}

至于FatalExecutionEngineError，我认为结构DFS_STORAGE_INFO_1的大小被错误地计算了，因为它的定义不正确。当尝试将指针转换到它们引用的结构时，下一个索引是错误的，因为大小是关闭的。在转换内存块时，它可能引用了一个本不应该访问的块，从而抛出了“访问被拒绝(0x0000005)”错误。