如何PInvoke的结构从GetTokenInformation（可变长度数组）安全地用于32位和64位？ C＃

问题描述

我下面提供的PInvoke code here但我在变长数组为size = 1的编组略有惊，然后通过它步进通过计算偏移，而不是索引到一个数组。是不是有更好的办法？如果没有的话，我应该怎么做，使之安全的32位和64位？

I'm following the pinvoke code provided here but am slightly scared by the marshalling of the variable-length array as size=1 and then stepping through it by calculating an offset instead of indexing into an array. Isn't there a better way? And if not, how should I do this to make it safe for 32-bit and 64-bit?

    [StructLayout(LayoutKind.Sequential)]
    public struct SID_AND_ATTRIBUTES
    {
        public IntPtr Sid;
        public uint Attributes;
    }

    [StructLayout(LayoutKind.Sequential)]
    public struct TOKEN_GROUPS
    {
        public int GroupCount;
        [MarshalAs(UnmanagedType.ByValArray, SizeConst = 1)]
        public SID_AND_ATTRIBUTES[] Groups;
    };


public void SomeMethod()
{
    IntPtr tokenInformation;

    // ... 

    string retVal = string.Empty;
    TOKEN_GROUPS groups = (TOKEN_GROUPS)Marshal.PtrToStructure(tokenInformation, typeof(TOKEN_GROUPS));
    int sidAndAttrSize = Marshal.SizeOf(new SID_AND_ATTRIBUTES());
    for (int i = 0; i < groups.GroupCount; i++)
    {
        // *** Scary line here: 
        SID_AND_ATTRIBUTES sidAndAttributes = (SID_AND_ATTRIBUTES)Marshal.PtrToStructure(
              new IntPtr(tokenInformation.ToInt64() + i * sidAndAttrSize + IntPtr.Size), 
              typeof(SID_AND_ATTRIBUTES));

    // ... 
}

我看<一href="http://stackoverflow.com/questions/3338297/managed-to-unmanaged-$c$c-call-causes-access-violation-sometimes">here宣布数组的长度一样多大于它很可能是，但似乎有其自身的问题的另一种方法。

I see here another approach of declaring the length of the array as much bigger than it's likely to be, but that seemed to have its own problems.

作为一个方面的问题：当我通过上面的code在调试步骤，我无法评价 tokenInformation.ToInt64（）或 ToInt32（）。我得到一个ArgumentOutOfRangeException。但是，code行执行就好了！？这是怎么回事吗？

As a side question: When I step through the above code in the debugger I'm not able to evaluate tokenInformation.ToInt64() or ToInt32(). I get an ArgumentOutOfRangeException. But the line of code executes just fine!? What's going on here?

推荐答案

我认为它看起来还行 - 作为没关系，任何非托管的土地戳的是，反正

I think it looks okay -- as okay as any poking about in unmanaged land is, anyway.

不过，我不知道为什么一开始是 tokenInformation.ToInt64（）+ IntPtr.Size ，而不是 tokenInformation.ToInt64（）+ 4 （作为GroupCount字段类型是int，而不是IntPtr的）。这是包装的结构/对齐或只是有鬼？我不知道在这里。

However, I wonder why the start is tokenInformation.ToInt64() + IntPtr.Size and not tokenInformation.ToInt64() + 4 (as the GroupCount field type is an int and not IntPtr). Is this for packing/alignment of the structure or just something fishy? I do not know here.

使用 tokenInformation.ToInt64（）是很重要的，因为在64位机的会爆炸的（发生OverflowException）如果IntPtr的值大于什么int可以存储。但是，CLR将处理长就好在这两种体系结构，它并不会改变从提取的IntPtr（因此实​​际值放回新的IntPtr（...））。

Using tokenInformation.ToInt64() is important because on a 64-bit machine will explode (OverflowException) if the IntPtr value is larger than what an int can store. However, the CLR will handle a long just fine on both architectures and it doesn't change the actual value extracted from the IntPtr (and thus put back into the new IntPtr(...)).

想象这样（未经测试）功能，以方便包装：

Imagine this (untested) function as a convenience wrapper:

// unpacks an array of structures from unmanaged memory
// arr.Length is the number of items to unpack. don't overrun.
void PtrToStructureArray<T>(T[] arr, IntPtr start, int stride) {
   long ptr = start.ToInt64();
   for (int i = 0; i < arr.Length; i++, ptr += stride) {
       arr[i] = (T)Marshal.PtrToStructure(new IntPtr(ptr), typeof(T));
   }
}

var attributes = new SID_AND_ATTRIBUTES[groups.GroupCount];
PtrToStructureArray(attributes, new IntPtr(tokenInformation.ToInt64() + IntPtr.Size), sidAndAttrSize);

快乐编码。

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