统计一个大文本行数的几种方法以及效率统计（二）

.NET4.0 + MemoryMapping + ReadByte()

该方法的思路主要是通过内存映射的原理，访问文件内容，由于在.net环境下不能一次性映射太大的文件，所以仍然采用分块映射的方式：

主要代码如下：

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/// <summary> /// MemoryMapping + ReadByte() /// </summary> unsafe static void CalulateLine_MemoryMapping_ReadByte(uint oneBlockSize) {     const string FILE_MAPPING_NAME = "~MappingTemp";     const int LINE_MIN_SIZE = 30;       long lineCount = 0;       IntPtr fileHandle = ShareMemory.CreateFile(         FILE_NAME,         ShareMemory.GENERIC_READ | ShareMemory.GENERIC_WRITE,         FileShare.Read | FileShare.Write,         IntPtr.Zero,         FileMode.Open,         ShareMemory.FILE_ATTRIBUTE_NORMAL | ShareMemory.FILE_FLAG_SEQUENTIAL_SCAN,         IntPtr.Zero);       uint fileSize = ShareMemory.GetFileSize(fileHandle, IntPtr.Zero);       if (ShareMemory.INVALID_HANDLE_VALUE != (int)fileHandle)     {         IntPtr mappingHandle = ShareMemory.CreateFileMapping(             (int)fileHandle,             IntPtr.Zero,             ShareMemory.PAGE_READWRITE,             0,             0,             FILE_MAPPING_NAME);         if (mappingHandle != IntPtr.Zero)         {             uint mapFlag = 0;               while (mapFlag <= fileSize)             {                 uint eachMappingSize = oneBlockSize;                 if (fileSize - mapFlag < oneBlockSize)                 {                     eachMappingSize = fileSize - mapFlag;                 }                   IntPtr pHead = ShareMemory.MapViewOfFile(                 mappingHandle,                 (uint)(ShareMemory.FILE_MAP_READ),                 0,                 mapFlag,                 eachMappingSize);                   int lastError = ShareMemory.GetLastError();                   if (pHead != IntPtr.Zero)                 {                       long flag = 0;                     while (flag < eachMappingSize)                     {                         //byte* pbHead= (byte*)pHead;                         //byte temp = *(pbHead + flag);                           byte temp = Marshal.ReadByte((IntPtr)((int)pHead + flag));                           if (temp == 0x0D)                         {                             lineCount++;                             flag += LINE_MIN_SIZE;                         }                         flag++;                     }                       ShareMemory.UnmapViewOfFile(pHead);                 }                 mapFlag += oneBlockSize;             }               ShareMemory.CloseHandle(mappingHandle);         }         ShareMemory.CloseHandle(fileHandle);       } }

测试结果：

.NET4.0 + MemoryMapping + Unsafe

使用unsafe代码，就是在上面代码的基础上，做了一些简单的修改。

 

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1 2	byte* pbHead = (byte*)pHead; byte temp = *(pbHead + flag);

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测试结果：