byte []數組到struct的可變長度數組

Question

我從套接字接收一個字節數組，字節結構只是一個固定寬度字符串的大字符數組。 在某些情況下，最后一個字段是動態的（而不是固定長度），我試圖將字節元素化為結構。 我已經讀過可變長度char數組需要是IntPtr，但我還沒弄清楚如何用剩余的字節來制作它。 我還讀過一些文章，我可能需要第二種結構，但仍然無法弄清楚如何正確地制造它。

這是一個這樣的網站

在結構中處理可變長度char數組的正確方法是什么？

結構：

[StructLayout(LayoutKind.Sequential, CharSet = CharSet.Ansi)]
public struct Header
{
    #region private member fields

    [MarshalAs(UnmanagedType.ByValArray, SizeConst = 16)]
    private char[] _f1;

    [MarshalAs(UnmanagedType.ByValArray, SizeConst = 16)]
    private char[] _f2;

    [MarshalAs(UnmanagedType.ByValArray, SizeConst = 16)]
    private char[] _f3;

    [MarshalAs(UnmanagedType.ByValArray, SizeConst = 16)]
    private char[] _f4;

    [MarshalAs(UnmanagedType.ByValArray, SizeConst = 16)]
    private char[] _f5;

    [MarshalAs(UnmanagedType.ByValArray, SizeConst = 16)]
    private char[] _f6;

    [MarshalAs(UnmanagedType.ByValArray, SizeConst = 4)]
    private char[] _f7;

    [MarshalAs(UnmanagedType.ByValArray, SizeConst = 12)]
    private char[] _f8;

    [MarshalAs(UnmanagedType.ByValArray, SizeConst = 32)]
    private char[] _f9;

    [MarshalAs(UnmanagedType.ByValArray, SizeConst = 16)]
    private char[] _f10;

    // how would this get filled with a char[] array from the byte array?
    public IntPtr VariableLengthData;

    #endregion
}

功能：

public static Header FromArray(byte[] array)
{
    IntPtr buff = IntPtr.Zero;

    try
    {
        int objsize = Marshal.SizeOf(typeof(Header));
        buff = Marshal.AllocHGlobal(objsize);
        Marshal.Copy(array, 0, buff, objsize);
        var result = (Header)Marshal.PtrToStructure(buff, typeof(HostHeader));

        // the variable length data needs to be filled in somehow
        // but also note that an extra 4 bytes was added to the size
        // of the struct with the IntPtr
        if(objsize < array.Length)
        {
            Marshal.Copy(array, array.Length - objsize, result.VariableLengthData, array.Length - objsize);
        }

        return result;
    }
    finally
    {
        if (buff != IntPtr.Zero)
        {
            Marshal.FreeHGlobal(buff);
            buff = IntPtr.Zero;
        }
    }
}

這有效 - 但現在Marshal.SizeOf（headerObj）說它比我嘗試將其轉換回byte []數組時的實際值要小。 除此之外，這個解決方案有什么問題嗎？

[StructLayout(LayoutKind.Sequential, CharSet = CharSet.Ansi)]
public struct Header
{
    [MarshalAs(UnmanagedType.ByValArray, SizeConst = 8)] 
    public char[] Field1;

    [MarshalAs(UnmanagedType.ByValArray, SizeConst = 8)] 
    public char[] Field2;

    [MarshalAs(UnmanagedType.ByValArray, SizeConst = 8)] 
    public char[] Field3;

    [MarshalAs(UnmanagedType.ByValArray, SizeConst = 1)]
    public char[] Field4;
}

public static Header DeserializeHeader(byte[] data)
{
    int objsize = Marshal.SizeOf(typeof(Header));
    IntPtr buff = Marshal.AllocHGlobal(objsize);
    Marshal.Copy(data, 0, buff, objsize);
    var header = (Header)Marshal.PtrToStructure(buff, typeof(Header));
    Marshal.FreeHGlobal(buff);

    // resize Field4 to hold all the remaining bytes
    if(objsize < data.Length)
    {
        header.Field4 = Encoding.ASCII.GetChars(data, objsize - header.Field4.Length, data.Length - objsize - header.Field4.Length);
    }
    return header;
}

Answer 1

只是不要太努力使您的C＃聲明與數據包格式完全匹配。 你喜歡這個：

[StructLayout(LayoutKind.Sequential, CharSet = CharSet.Ansi, Pack = 1)]
public class Header {
    //....
}

public class Packet {
    public Header Header;
    public byte[] VariableLengthData;
}

現在變得簡單了。 您可以一舉封送標題，只需復制存在的額外字節：

static unsafe Packet FromArray(byte[] data) {
    var hdrsize = Marshal.SizeOf(typeof(Header));
    if (data.Length < hdrsize) throw new ArgumentException();
    Packet result = new Packet();
    // Marshal the header
    fixed (byte* pdata = &data[0]) {
        result.Header = (Header)Marshal.PtrToStructure(new IntPtr(pdata), typeof(Header)); 
    }
    // Copy the rest
    var varsize = data.Length - hdrsize;
    result.VariableLengthData = new byte[varsize];
    Array.Copy(data, hdrsize, result.VariableLengthData, 0, varsize);
    return result;
}

並根據需要修改Packet類，您可能希望添加一堆屬性來處理char []。