c++ - How should I read the filename in FILE_NOTIFY_INFORMATION struct -


i'm trying monitor file changes not sure on how read filename in file_notify_information struct:

    handle dwchangehandles[2];     dword dwwaitstatus;     wchangehandles[0] = findfirstchangenotification(dirname.c_str(), false, file_notify_change_last_write);     if (dwchangehandles[0] == invalid_handle_value) printerr(__file__,__line__,"findfirstchangenotification function failed.\n");     ...     if ((dwchangehandles[0] == null) || (dwchangehandles[1] == null))  //final validation         printerr(__file__,__line__,"unexpected null findfirstchangenotification.\n");      while (true) {         std::cout << "waiting notification...\n";         dwwaitstatus = waitformultipleobjects(2, dwchangehandles, false, infinite);         if(dwwaitstatus==wait_object_0){             std::cout << "something changed\n";              dword bytesreturned;             size_t buflen = 1024;             file_notify_information buffer[buflen];             if (readdirectorychangesw(dwchangehandles[0], buffer, buflen, false, file_notify_change_last_write, &bytesreturned, null, null)){                 std::wcout << std::wstring(buffer->filename)<< std::endl; //there nothing in expected output here             }             if (findnextchangenotification(dwchangehandles[0]) == false ) printerr(__file__,__line__,"findnextchangenotification function failed.\n");         }          else if(dwwaitstatus==wait_timeout) printerr(__file__,__line__,"no changes in timeout period.\n");         else printerr(__file__,__line__,"unhandled dwwaitstatus.\n");     }

is there doing wrong

you have number of problems can see immediately:

  1. according docs readdirectorychangesw function, buffer needs dword-aligned. using buffer on stack isn't guaranteed - should allocate 1 heap instead.

  2. you don't seem using function correctly. call readdirectorychangesw first, , then wait on event. not other way around. when readdirectorychangesw returns asynchronous call there no data in buffer @ point. need wait notification request has been completed before using buffer contents.

  3. findnextchangenotification used findfirstchangenotification, wrong. when readdirectorychangesw completes need use nextentryoffset field in file_notify_information structure loop through returned events.

edit: since you've added more code question it's obvious mixing 2 apis. findfirstchangenotification , findnextchangenotification 1 api, , readdirectorychangesw another. believe you've been confused passage in docs:

this function not indicate change satisfied wait condition. retrieve information specific change part of notification, use readdirectorychangesw function.

i guess confusion understandable, 2 apis can't used together. if you're using findfirstchangenotification notification something changed, , have re-read directory find out was. if want specific notifications @ file level have use readdirectorychangesw monitoring.


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