内存映射文件处理大文件

bool DisposeBigFile( const string& strFilePath )
{
	// 创建文件对象
	bool bRet = false;
	HANDLE hFile = INVALID_HANDLE_VALUE;
	HANDLE hFileMap = NULL;
	do 
	{
		hFile = CreateFile(strFilePath.c_str(), GENERIC_READ | GENERIC_WRITE,0, NULL, OPEN_EXISTING, FILE_ATTRIBUTE_NORMAL, NULL);
		if (INVALID_HANDLE_VALUE == hFile)
		{
			TRACE("创建文件对象失败,错误代码:%d\r\n", GetLastError());
			break;
		}

		// 得到系统分配粒度
		SYSTEM_INFO stSysInfo;
		GetSystemInfo(&stSysInfo);
		DWORD dwGran = stSysInfo.dwAllocationGranularity;
		// 得到文件尺寸
		DWORD dwFileSizeHigh;
		__int64 qwFileSize = GetFileSize(hFile, &dwFileSizeHigh);
		qwFileSize |= (((__int64)dwFileSizeHigh) << 32);
		if(0 == qwFileSize)
		{
			bRet = true;
			break;
		}

		// 创建文件映射对象
		hFileMap = CreateFileMapping(hFile, NULL, PAGE_READWRITE, 0, 0, NULL);
		if (NULL == hFileMap)
		{
			TRACE("创建文件映射对象失败,错误代码:%d\r\n", GetLastError());
			break;
		}

		// 偏移地址 
		__int64 qwFileOffset = 0;
		
		// 块大小
		DWORD dwBlockBytes = 1000 * dwGran;

		while (qwFileSize > 0)
		{
			if (qwFileSize < 1000 * dwGran)
			{
				dwBlockBytes = (DWORD)qwFileSize;
			}

			// 映射视图
			LPBYTE lpbMapAddress = (LPBYTE)MapViewOfFile(hFileMap,FILE_MAP_ALL_ACCESS, 
														(DWORD)(qwFileOffset >> 32),
														(DWORD)(qwFileOffset & 0xFFFFFFFF),
														dwBlockBytes);
			if (NULL == lpbMapAddress)
			{
				TRACE("映射文件映射失败,错误代码:%drn", GetLastError());
				break;
			}

			// 对映射的视图进行访问
			for(DWORD i = 0; i < dwBlockBytes; i++)
			{
				BYTE lpbytetemp = *(lpbMapAddress + i);
			}

			// 撤消文件映像
			UnmapViewOfFile(lpbMapAddress);

			// 修正参数
			qwFileOffset += dwBlockBytes;
			qwFileSize -= dwBlockBytes;
		}

		if(qwFileSize <= 0)
		{
			bRet = true;
		}
	} while (false);
	
	if(NULL != hFileMap)
	{
		// 关闭文件映射对象句柄
		CloseHandle(hFileMap);
		hFileMap = NULL;
	}

	if(INVALID_HANDLE_VALUE != hFile)
	{
		// 关闭文件对象
		CloseHandle(hFile);
		hFile = INVALID_HANDLE_VALUE;
	}
	return bRet;
}