C#記憶體映射大文件並使用Marshal解析結構體信息

記憶體映射數據處理類主要函數及變數如下：

 1        string _filepath;
 2        /// <summary>
 3         /// 引用記憶體映射文件
 4         /// </summary>
 5         private MemoryMappedFile _memoryFile = null;
 6         /// <summary>
 7         /// 用於訪問記憶體映射文件的存取對象
 8         /// </summary>
 9         private MemoryMappedViewAccessor _accessor = null;
10         public ScientificData _ScientificData = new ScientificData();
11         long _lenByte = 0;
12         public DatFileInfo(string filepath)
13         {
14             _filepath = filepath;
15             _memoryFile = MemoryMappedFile.CreateFromFile(_filepath);
16             _accessor = _memoryFile.CreateViewAccessor();
17             // _stream = _memoryFile.CreateViewStream();
18             FileInfo finfo = new FileInfo(filepath);
19             _lenByte = finfo.Length;//文件位元組大小
20         }
21         public void SaveRawData(string savepath)
22         {
23             
24             int currentByteNum = 0;//當前位元組位置
25             uint ACountint = 0;
26             uint RCountint = 0;
27             ScientificData scientificData = new ScientificData();
28             byte[] data = new byte[1036 * 1036];
29             while (currentByteNum<= (_lenByte- 1036 * 1036))
30             {
31                 _accessor.Read<uint>(currentByteNum, out RCountint);
32                 _accessor.Read<uint>(currentByteNum+4, out ACountint);
33                 if (RCountint < 1400 && ACountint < 1401 && _accessor.ReadByte(currentByteNum+8)==0x0a && _accessor.ReadByte(currentByteNum + 9) == 0x0b)//初步判斷條件，節省解析結構體時間
34                 {
35                     _accessor.ReadArray(currentByteNum, data, 0, data.Length);//讀取結構體數據到位元組數組
36                     scientificData = ByteToStructure<ScientificData>(data);//位元組數組解析到結構體
37                     if((scientificData.aux_3a1 == 0x3A) && (scientificData.aux_3a3 == 0x3A))//進一步判斷
38                     {
39                         ushort[,] sdata = scientificData.GetImageData();//得到所需的數據
40                         saveRawData(savepath + ((int)((ACountint - 1)/15+1)).ToString()+ "_" + (ACountint-1).ToString() + "_"+ACountint + "_"+scientificData.aux_num + ".raw" , sdata);
41                         currentByteNum += 1036 * 1036;
42                     }
43                     else
44                         currentByteNum++;
45                 }
46                 else
47                     currentByteNum++;
48 
49 
50             }
51         }
52         /// <summary>
53         /// 由byte數組轉換為結構體
54         /// </summary>
55         public static T ByteToStructure<T>(byte[] dataBuffer)
56         {
57             object structure = null;
58             int size = Marshal.SizeOf(typeof(T));
59             IntPtr allocIntPtr = Marshal.AllocHGlobal(size);
60             try
61             {
62                 Marshal.Copy(dataBuffer, 0, allocIntPtr, size);
63                 structure = Marshal.PtrToStructure(allocIntPtr, typeof(T));
64             }
65             finally
66             {
67                 Marshal.FreeHGlobal(allocIntPtr);
68             }
69             return (T)structure;
70         }
71         private void saveRawData(string savepath,ushort[,] data)
72         {
73             int len = data.Length*2;
74             byte[] bdata = new byte[len];
75             Buffer.BlockCopy(data,0,bdata,0,len);
76             File.WriteAllBytes(savepath, bdata);
77         }
78         /// <summary>
79         /// 由結構體轉換為byte數組
80         /// </summary>
81         public static byte[] StructureToByte<T>(T structure)
82         {
83             int size = Marshal.SizeOf(typeof(T));
84             byte[] buffer = new byte[size];
85             IntPtr bufferIntPtr = Marshal.AllocHGlobal(size);
86             try
87             {
88                 Marshal.StructureToPtr(structure, bufferIntPtr, true);
89                 Marshal.Copy(bufferIntPtr, buffer, 0, size);
90             }
91             finally
92             {
93                 Marshal.FreeHGlobal(bufferIntPtr);
94             }
95             return buffer;
96         }

科學數據結構體定義如下：

  //一幅1036*1036位元組數據定義
    public struct ScientificData
     {
        /參數信息
     [MarshalAs(UnmanagedType.ByValArray, SizeConst = 4)]
       public byte[] RelativePacketCount;
      [MarshalAs(UnmanagedType.ByValArray, SizeConst = 4)]
       public Byte[] AbsolutePacketCount;
     ........
      public byte aux_3a;//填充3A H
       .........
      [MarshalAs(UnmanagedType.ByValArray, SizeConst = 1036)]
        public OneImageRow[] ImageData;//圖像數據行
/// <summary>
/// 獲取raw圖數據
/// </summary>
/// <returns>圖像數據</returns>
public ushort[,] GetImageData()
{
ushort[,] rawdata = new ushort[1036, 512];
for (int i = 0; i < 1036; i++)
{
var onerow = ImageData[i];
for (int j = 0; j < 512; j++)
{
rawdata[i, j] = (ushort)(((onerow.imagedata[j * 2] << 8) | onerow.imagedata[j * 2 + 1])) ;
}
}
return rawdata;
}
}

圖像數據結構體如下：

    public struct OneImageRow
    {
        [MarshalAs(UnmanagedType.ByValArray, SizeConst = 4)]
        public byte[] RelativePacketCount;
        [MarshalAs(UnmanagedType.ByValArray, SizeConst = 4)]
        public byte[] AbsolutePacketCount;
        [MarshalAs(UnmanagedType.ByValArray, SizeConst = 2)]
        public byte[] linehead;//行頭
        [MarshalAs(UnmanagedType.ByValArray, SizeConst = 2)]
        public byte[] linenum;//行號
        [MarshalAs(UnmanagedType.ByValArray, SizeConst = 1024)]
        public byte[] imagedata;//圖像數據512×2=1024位元組
                              
        public static string ByteToHex(byte[] bt)
        {
            var hex = BitConverter.ToString(bt, 0).ToUpper();
            return hex;
        }
    }