将复杂结构写入内存映射文件 [英] Writing complex structure to memory-mapped-file

问题描述

我尝试将以下结构写入内存映射文件，但数组仍然有问题(写入时抛出异常，结构不能包含引用)

I try to write following struct to a memory mapped file, but I still have problem with the array (writing throws exception that the struct can not contain reference)

[StructLayout(LayoutKind.Explicit)]
struct IndexEntry {
    [FieldOffset(0)]
    public byte key;

    [FieldOffset(4)]
    public int lastValueIdx;

    [FieldOffset(8)]
    [MarshalAs(UnmanagedType.ByValArray, SizeConst = Constants.PART_ENTRY_SIZE)]
    public long[] values;
}

我用这个电话来写作:

UnmanagedMemoryAccessor.Write<IndexEntry>(0, ref entry);

你能告诉我，我做错了什么吗?谢谢

Can you please tell me, what am I doing wrong? Thx

推荐答案

解决方案是使用固定大小的数组和不安全的代码.所以结构应该是这样的:

The solution of this is using the fixed size array and unsafe code. So the struct should look like this:

[StructLayout(LayoutKind.Explicit)]
unsafe struct IndexEntry {
    [FieldOffset(0)]
    public byte key;

    [FieldOffset(1)]
    public int lastValueIdx;

    [FieldOffset(5)]
    [MarshalAs(UnmanagedType.ByValArray, SizeConst = Constants.PART_ENTRY_SIZE)]
    public fixed long values[Constants.PART_ENTRY_SIZE];
}

请注意，必须使用/unasfe"选项编译程序(或包含该结构的单个项目)，然后必须像这样访问数组:

Note that the program (or a single project containing that struct) must be compiled with the "/unasfe" option and the array must be then accessed like this:

fixed(long* arr = this.values) {
    // Setting value
    arr[index] = value;
}
unsafe {
    // Getting value
    x = obj.values[index];
}

然后 UnmanagedMemoryAccessor.Write(...) 和 UnmanagedMemoryAccessor.Read(...) 函数完美运行.

Then the UnmanagedMemoryAccessor.Write<T>(...) and UnmanagedMemoryAccessor.Read<T>(...) functions work perfectly.

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