FSEvents C++ Example - c++

Question

I need to create FSEvents watcher for a Folder in Mac. I'm comfortable with C++ and is there a way to get FSEvents notifications in C++ code, rather than Objective-C. Is there some example code to start with and any libraries i need to include ..?
I'm already on this page.
http://developer.apple.com/library/mac/#featuredarticles/FileSystemEvents/_index.html
But there seems to be only Objective C, can i have CPP version of it

Answer 1

Yes, it is possible in C. You should look for Kernel Queues.
Here's a small sample to watch the directory:
#include <errno.h> // for errno
#include <fcntl.h> // for O_RDONLY
#include <stdio.h> // for fprintf()
#include <stdlib.h> // for EXIT_SUCCESS
#include <string.h> // for strerror()
#include <sys/event.h> // for kqueue() etc.
#include <unistd.h> // for close()
int main (int argc, const char *argv[])
{
int kq = kqueue ();
// dir name is in argv[1], NO checks for errors here
int dirfd = open (argv[1], O_RDONLY);
struct kevent direvent;
EV_SET (&direvent, dirfd, EVFILT_VNODE, EV_ADD | EV_CLEAR | EV_ENABLE,
NOTE_WRITE, 0, (void *)dirname);
kevent(kq, &direvent, 1, NULL, 0, NULL);
// Register interest in SIGINT with the queue. The user data
// is NULL, which is how we'll differentiate between
// a directory-modification event and a SIGINT-received event.
struct kevent sigevent;
EV_SET (&sigevent, SIGINT, EVFILT_SIGNAL, EV_ADD | EV_ENABLE, 0, 0, NULL);
// kqueue event handling happens after the legacy API, so make
// sure it doesn eat the signal before the kqueue can see it.
signal (SIGINT, SIG_IGN);
// Register the signal event.
kevent(kq, &sigevent, 1, NULL, 0, NULL);
while (1) {
// camp on kevent() until something interesting happens
struct kevent change;
if (kevent(kq, NULL, 0, &change, 1, NULL) == -1) { exit(1); }
// The signal event has NULL in the user data. Check for that first.
if (change.udata == NULL) {
break;
} else {
// udata is non-null, so it's the name of the directory
printf ("%s\n", (char*)change.udata);
}
}
close (kq);
return 0;
}
The details can be found in ch. 16 (kqueues and FSEvents) of "Advanced Mac OSX Programming" by Mark Dalrymple. The additional info may be found in *BSD documentation for kqueues.
Or use this API from FSEvents (it's mostly C-based).
FSEventStreamRef FSEventStreamCreate (CFAllocatorRef allocator,
FSEventStreamCallback callback,
FSEventStreamContext *context,
CFArrayRef pathsToWatch,
FSEventStreamEventId sinceWhen,
CFTimeInterval latency,
FSEventStreamCreateFlags flags);
to create the FSEvents event stream with pure-C callback.
Then attach this event stream to your runloop using the
void FSEventStreamScheduleWithRunLoop (FSEventStreamRef streamRef,
CFRunLoopRef runLoop,
CFStringRef runLoopMode);
Yes, here you probably should use a line of Obj-C to get the RunLoop handle: get the CFRunLoop from an NSRunLoop by using -getCFRunLoop
CFRunLoop* loopRef = [[NSRunLoop currentRunLoop] getCFRunLoop];
or use the pure C call
CFRunLoop* loopRef = CFRunLoopGetCurrent();
Start the event stream with
Boolean FSEventStreamStart (FSEventStreamRef streamRef);
Stop the event stream with
void FSEventStreamStop (FSEventStreamRef streamRef);
And then unschedule it from the runloop with this:
void FSEventStreamUnscheduleFromRunLoop (FSEventStreamRef streamRef,
CFRunLoopRef runLoop,
CFStringRef runLoopMode);
Invalidate the stream (cleanup):
void FSEventStreamInvalidate (FSEventStreamRef streamRef);
Hope this will get you started.