Marshal.PtrToStructure抛出AccessViolationException [英] Marshal.PtrToStructure throwing AccessViolationException

问题描述

我有这个结构：

    [StructLayout(LayoutKind.Sequential)]
    public struct IS
    {
    public UInt32 ID; 
    public UInt32 Quality; 
    public UInt32 Flags;
    public UInt32 Flags2;     
    public UInt32 ContainerSlots; 
    [MarshalAs(UnmanagedType.ByValArray, SizeConst = 10)]
    public Int32[] ItemStatType;  
    [MarshalAs(UnmanagedType.ByValArray, SizeConst = 10)]
    public UInt32[] ItemStatValue;    
    [MarshalAs(UnmanagedType.ByValArray, SizeConst = 10)]
    public Int32[] ItemStatUnk1;    
    [MarshalAs(UnmanagedType.ByValArray, SizeConst = 10)]
    public Int32[] ItemStatUnk2;       
    public UInt32 ScalingStatDistribution; 
    public UInt32 DamageType;      
    public UInt32 Delay;      
    public float RangedModRange;
    [MarshalAs(UnmanagedType.ByValArray, SizeConst = 5)]
    public Int32[] SpellId;          
    [MarshalAs(UnmanagedType.ByValArray, SizeConst = 5)]
    public Int32[] SpellTrigger;       
    [MarshalAs(UnmanagedType.ByValArray, SizeConst = 5)]
    public Int32[] SpellCharges;  
    [MarshalAs(UnmanagedType.ByValArray, SizeConst = 5)]
    public Int32[] SpellCooldown;   
    [MarshalAs(UnmanagedType.ByValArray, SizeConst = 5)]
    public Int32[] SpellCategory;     
    [MarshalAs(UnmanagedType.ByValArray, SizeConst = 5)]
    public Int32[] SpellCategoryCooldown;
    public UInt32 Bonding; 
    public string Name;       
    public string Name2;                  
    public string Name3;         
    [MarshalAs(UnmanagedType.ByValArray, SizeConst = 3)]
    public UInt32[] Color;  
    [MarshalAs(UnmanagedType.ByValArray, SizeConst = 3)]
    public UInt32[] Content;
};

我试图从文件中读取字节并将这些字节复制到上面的 struct 使用Marshal和GCHandle，我的代码如下：

And I'm trying to read bytes from a file and copy those bytes to the above struct using Marshal and a GCHandle, my code is as follows:

reader = BinaryReader.FromFile(fileName);
m_rows = new List<IS>();
int size = Marshal.SizeOf(typeof(IS));
if(reader.BaseStream.Length < size)
  return;
byte[] buffer = new byte[size];
buffer = reader.ReadBytes(size);
GCHandle handle = GCHandle.Alloc(buffer, GCHandleType.Pinned);
m_rows.Add((IS)Marshal.PtrToStructure(handle.AddrOfPinnedObject(), typeof(IS)));
handle.Free();

但我得到一个 AccessViolationException：尝试读或写受保护的内存

But I'm getting an AccessViolationException : attempt to read or write protected memory

我不知道为什么会抛出此异常。

I have no idea why this exception is thrown.

推荐答案

我没有立即看到错误，并写了一个测试程序来重现问题。使用二进制搜索找到问题，重复注释一半字段，直到我把它缩小到：

I didn't see the bug immediately and wrote a little test program to repro the problem. Using binary search to find the issue, commenting half the fields out repeatedly until I narrowed it down to:

[StructLayout(LayoutKind.Sequential)]
public struct IS {
    public string Name;
}

这不能工作，pinvoke marshaller假定为​​ string 来自C字符串， char * 。这不可能纠正从文件读取的数据，它不能包含有效的指针。 AccessViolation在尝试解除引用指针时被触发。

That cannot work, the pinvoke marshaller assumes the default marshaling for string is from a C string, char*. That cannot possibly correct for data that you read from a file, it can never contain valid pointers. The AccessViolation is triggered when it tries to dereference the pointer.

问题中没有提示猜测字符串是如何实际序列化到文件中的。 正常方式是：

There are no hints in the question to guess how the string was actually serialized to the file. The normal way is:

[StructLayout(LayoutKind.Sequential, CharSet = CharSet.Ansi)]
public struct IS {
    [MarshalAs(UnmanagedType.ByValTStr, SizeConst = 42)]
    public string Name;
};

如有必要，使用十六进制查看器来找出SizeConst的正确值。如果编码是不寻常的（不是系统默认页面），那么你必须声明它为byte []并使用正确的编码转换它。

Use a hex viewer if necessary to figure out the proper value of SizeConst. If the encoding is unusual (not the system default page) then you have to declare it as byte[] and use the proper Encoding to convert it.

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