losing files when using ReadDirectoryChangesW - winapi

Question

I'm using ReadDirectoryChangesW to monitor a directory.
Here's my simple code
#include <windows.h>
#include <stdlib.h>
#include <stdio.h>
#include <tchar.h>
#include <iostream>
#include <string>
#include <cwctype>
using namespace std;
wstring getname(FILE_NOTIFY_INFORMATION *tmp)
{
wstring s = L"";
for (int i = 0;i < tmp->FileNameLength / 2;i++)
s += tmp->FileName[i];
return s;
}
void _tmain(int argc, TCHAR *argv[])
{
HANDLE hDir;
char notify[1024];
DWORD cbBytes,i;
char AnsiChar[3];
wchar_t UnicodeChar[2];
LPTSTR path;
FILE_NOTIFY_INFORMATION *pnotify=(FILE_NOTIFY_INFORMATION *)notify;
FILE_NOTIFY_INFORMATION *tmp ;
// GetCurrentDirectory(MAX_PATH,path.GetBuffer(MAX_PATH+1));
wcout.imbue(locale("chs"));
path = argv[1];
hDir = CreateFile( path, FILE_LIST_DIRECTORY,
FILE_SHARE_READ |
FILE_SHARE_WRITE |
FILE_SHARE_DELETE, NULL,
OPEN_EXISTING, FILE_FLAG_BACKUP_SEMANTICS |
FILE_FLAG_OVERLAPPED, NULL);
wcout << L"===CreateFile complete===" << endl;
if (hDir == INVALID_HANDLE_VALUE)
{
wcout << L"invalid handle value" << endl;
return;
}
FILE_NOTIFY_INFORMATION buffer[1024];
FILE_NOTIFY_INFORMATION *pbuffer;
while (TRUE)
{
wcout << L"waiting..." << endl;
if(ReadDirectoryChangesW(hDir, &buffer, sizeof(buffer),
TRUE, FILE_NOTIFY_CHANGE_FILE_NAME| FILE_NOTIFY_CHANGE_LAST_WRITE,
&cbBytes, NULL, NULL))
{
pbuffer = buffer;
do{
tmp = pbuffer;
switch(tmp->Action)
{
case FILE_ACTION_ADDED:
wcout << L"Directory/File added - " << getname(tmp) << endl;
break;
case FILE_ACTION_REMOVED:
wcout << L"Directory/File removed - " << getname(tmp) << endl;
break;
case FILE_ACTION_MODIFIED:
wcout << L"Directory/File modfied - " << getname(tmp) << endl;
break;
case FILE_ACTION_RENAMED_OLD_NAME:
wcout << L"Directory/File old name - " << getname(tmp) << endl;
break;
case FILE_ACTION_RENAMED_NEW_NAME:
wcout << L"Directory/File new name - " << getname(tmp) << endl;
break;
default:
wcout << L"unknown action\n" << endl;
break;
}
pbuffer += pbuffer->NextEntryOffset;
}while(pbuffer->NextEntryOffset);
} else
{
wcout << "readChangesW failed now return" << endl;
return;
}
}
}
It looks fine, however, when I'm adding or deleting a large number of files in my directory, it will not report some of the changes, how can I fix this?

Answer 1

Try making your buffer bigger.
From the documentation for the ReadDirectoryChangesW function:
When you first call ReadDirectoryChangesW, the system allocates a buffer to store change information. This buffer is associated with the directory handle until it is closed and its size does not change during its lifetime. Directory changes that occur between calls to this function are added to the buffer and then returned with the next call. If the buffer overflows, the entire contents of the buffer are discarded and the lpBytesReturned parameter contains zero.
The buffer size that the system allocates is based on the size of the buffer you pass in. If you pass in a bigger size the system will allocate a bigger buffer to store changes that occur while you are processing the previous lot of changes, which means there's less chance of the buffer overflowing and those changes being lost.