Monitoring directory using ReadDirectoryChangesW API - c

Question

I am trying to monitor a directory e:\test using ReadDirectoryChangesW API.
My Code :
#define UNICODE
#define WIN32_WINNT 0x0500
#include "stdafx.h"
#include <stdio.h>
#include <windows.h>
HANDLE hDir;
int _tmain(int argc, _TCHAR* argv[])
{
FILE_NOTIFY_INFORMATION fniDir;
DWORD i = 0;
hDir = CreateFile(_T("e:\\test"), GENERIC_READ , FILE_SHARE_READ, NULL, OPEN_EXISTING, FILE_FLAG_BACKUP_SEMANTICS, NULL);
ReadDirectoryChangesW(hDir, &fniDir, sizeof(fniDir), TRUE, FILE_NOTIFY_CHANGE_FILE_NAME, &i, NULL, NULL);
while(TRUE)
{
if(i>0)
wprintf(L"%s", fniDir.FileName);
}
CloseHandle(hDir);
return 0;
}
I don't know what's wrong with my code as I haven't understood ReadDirectoryChangesW documentation completely, specially the LPOVERLAPPED parameters.
When I run the code I don't get any output, except for a blank console window. Can someone point me in a right direction?
Thanks.

Answer 1

You only need the overlapped struct if you plan on catching the changes notifications asynchronously. In your code you don't need it.
Here's how you do it.
HANDLE hDir = CreateFile(
p.string().c_str(), /* pointer to the file name */
FILE_LIST_DIRECTORY, /* (this is important to be FILE_LIST_DIRECTORY!) access (read-write) mode */
FILE_SHARE_WRITE | FILE_SHARE_READ | FILE_SHARE_DELETE, /* (file share write is needed, or else user is not able to rename file while you hold it) share mode */
NULL, /* security descriptor */
OPEN_EXISTING, /* how to create */
FILE_FLAG_BACKUP_SEMANTICS, /* file attributes */
NULL /* file with attributes to copy */
);
if(hDir == INVALID_HANDLE_VALUE){
throw runtime_error(string("Could not open ").append(p.string()).append(" for watching!"));
}
FILE_NOTIFY_INFORMATION buffer[1024];
DWORD BytesReturned;
while( ReadDirectoryChangesW(
hDir, /* handle to directory */
&buffer, /* read results buffer */
sizeof(buffer), /* length of buffer */
TRUE, /* monitoring option */
FILE_NOTIFY_CHANGE_LAST_WRITE, /* filter conditions */
&BytesReturned, /* bytes returned */
NULL, /* overlapped buffer */
NULL)){
do{
//CANT DO THIS! FileName is NOT \0 terminated
//wprintf("file: %s\n",buffer.FileName);
buffer += buffer.NextEntryOffset;
}while(buffer.NextEntryOffset);
}