ReadDirectoryChangesW

ReadDirectoryChangesW函数，这个函数不仅能够监测到文件系统的变化，还能够返回详细的文件变动的信息，并且能够选择是使用同步方式检测还是异步方式监测，比较全面，但是这个函数的使用比较复杂，而且有一些需要注意的地方，把我这几天使用的心得记录一下吧，参考了MSDN以及老外的一些文档！

           首先是ReadDirectoryChangesW这个函数只在WinNT中能够使用，是新加的一个API函数，所以在VC++中使用该函数的时候需要在stdafx.h的#include <afxwin.h>的前面添加 #define _WIN32_WINNT 0x0500，实现的时候应该这样

#if(_WIN32_WINNT >= 0x0400)
WINBASEAPI
BOOL
WINAPI
ReadDirectoryChangesW(
           HANDLE hDirectory,
           LPVOID lpBuffer,
           DWORD nBufferLength,
           BOOL bWatchSubtree,
           DWORD dwNotifyFilter,
           LPDWORD lpBytesReturned,
           LPOVERLAPPED lpOverlapped,
           LPOVERLAPPED_COMPLETION_ROUTINE lpCompletionRoutine
           );
#endif /* _WIN32_WINNT >= 0x0400 */

WINBASEAPI

否则会出现编译错误的情况！delphi里使用的时候不用注意这些问题！

           其次，在文件系统更新很快，很频繁的时候，这个函数会出现漏掉监控信息的情况，这个原因在MSDN里有提到，MSDN里是这么说的：当你第一次调用ReadDirectoryChangesW这个函数的时候，系统会分配一些缓存来存储文件变化信息，这些缓存与要监控的文件夹关联，直到他关闭，并且这些缓存的大小在其生存期间不会改变，调用该函数的时候，文件的变化信息不断添加到这些缓存中，如果缓存溢出，这些改变信息会丢失，函数返回error_notify_enum_dir的错误。老外写了个类，据说解决了这个问题，我没有测试过，大家可以自己去看看！http://www.codeproject.com/file/directorychangewatcher.asp

msdn 查 Change Journals

Change Journals
An automatic backup application is one example of a program that must check for changes to the state of a volume to perform its task. The brute force method of checking for changes in directories or files is to scan the entire volume. However, this is often not an acceptable approach because of the decrease in system performance it would cause. Another method is for the application to register a directory notification (by calling the FindFirstChangeNotification or ReadDirectoryChangesW functions) for the directories to be backed up. This is more efficient than the first method, however, it requires that an application be running at all times. Also, if a large number of directories and files must be backed up, the amount of processing and memory overhead for such an application might also cause the operating system's performance to decrease.


To avoid these disadvantages, the NTFS file system maintains a change journal in Microsoft® Windows® 2000 and later. When any change is made to a file or directory in a volume, the change journal for that volume is updated with a description of the change and the name of the file or directory.

Change journals are also needed to recover file system indexing — for example after a computer or volume failure. The ability to recover indexing means the file system can avoid the time-consuming process of reindexing the entire volume in such cases.

The following topics discuss change journals: