FileSystemWatcher not firing events when file written using fprintf or printf

Question

Yes there are many similar questions but none of them address my unique situation.

There is a separate c++ process writing the file using c++ printf and fprintf. filename i am trying to watch is info_20160525.log

My fileSystemWatcher in winform C# application gets notification when the writer process writes to the file AND I physically access the file i-e F5 the folder or have it open in textpad and click the opened file or right click the file but I never get any event notification when I dont physically interact with the file. Also, when I shutdown the writer application I do get the notification.

Here is my code.

public bool StartUp(string fullfilepath, int linenumber)
{
        if (!File.Exists(fullfilepath))
            return false;
        if (!LogClass.CheckPathExists(m_applicationPath)) 
            return false;

        try
        {

            FileInfo info = new FileInfo(fullfilepath);

            m_filename = fullfilepath;
            m_fileWatcher = new FileSystemWatcher(info.DirectoryName, info.Name);
            m_fileWatcher.NotifyFilter = NotifyFilters.Attributes | NotifyFilters.LastAccess
       | NotifyFilters.LastWrite | NotifyFilters.Size ;    

            m_fileWatcher.Changed += m_fileWatcher_Changed;
            m_fileWatcher.Error += m_fileWatcher_Error;
            m_fileWatcher.Created += m_fileWatcher_Created;
            m_fileWatcher.Deleted += m_fileWatcher_Deleted;
            m_fileWatcher.Disposed += m_fileWatcher_Disposed;
            m_fileWatcher.Renamed += m_fileWatcher_Renamed;
            m_linesRead = linenumber;
            m_fileWatcher.EnableRaisingEvents = true;
        }
        catch(Exception e)
        {
            LogClass.LogError(e, "Trouble accessing the file" + fullfilepath, m_applicationPath);
        }
        return true;
}

These are the handlers. I have breakpoints in each one of them but I never get a trigger unless ofcourse I physically interact with the file.

    void m_fileWatcher_Renamed(object sender, RenamedEventArgs e)
    {
        string S = "";
    }

    void m_fileWatcher_Disposed(object sender, EventArgs e)
    {
        string S = "";
    }

    void m_fileWatcher_Deleted(object sender, FileSystemEventArgs e)
    {
        string S = "";
    }

    void m_fileWatcher_Created(object sender, FileSystemEventArgs e)
    {
        string S = "";
    }

    void m_fileWatcher_Error(object sender, ErrorEventArgs e)
    {
        string S = "";

    }

    void m_fileWatcher_Changed(object sender, FileSystemEventArgs args)
    {
        if (args.ChangeType == WatcherChangeTypes.Changed)
        {                
            while (ParseFile(args.FullPath))
            {

            }
        }
    }

Answer 1

I bet this thread has your answer --> FileSystemWatcher changed event (for “LastWrite”) is unreliable

The FileSystemWatcher uses an update to the LastWrite attribute of a file to fire events, however, the LastWrite is not updated in real time and should not be relied upon as trigger for an event.

If you have enough time and resources on your hands then you probably want to look into File System Filters and the simpler approach of a Filter Manager and Minifilter Driver. It is driver type development, however, it is a sure file way to accomplish your objective.

It is dug down a little deeper by system policy but gives you a wide array of events to latch onto. If I was doing this for anything like pci compliance or similar tasks then I would not use the FileSystemWatcher.