inotify_add_watch fails with no such file or directory - c++

Question

I am trying to watch for the creation of file in my c/c++ program. I am trying to use inotify for this purpose. However, I am getting a no such file or directory when I make the inotify_add_watch() call in my code. I am running my program on an Ubuntu 16.04 machine. The machine is running in the EC2 cloud. Can someone tell me the possible reasons for receiving a no such file or directory error?
According to the man page for inotify_add_watch, that's not even one of the possible error codes. I've made to sure I have proper read permissions for the file I am trying to monitor etc.
Here's my test program:
#include <stdio.h>
#include <stdlib.h>
#include <errno.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/inotify.h>
#include <limits.h>
#define MAX_EVENTS 1024
#define LEN_NAME 16
#define EVENT_SIZE (sizeof (struct inotify_event))
#define BUF_LEN (MAX_EVENTS * (EVENT_SIZE + LEN_NAME))
int
main(int argc, char **argv)
{
int length, i = 0, wd;
int fd;
char buffer[BUF_LEN];
/* Initialize Inotify*/
fd = inotify_init();
if (fd < 0) {
perror("Couldn't initialize inotify");
}
/* add watch to starting directory */
wd = inotify_add_watch(fd, argv[1], IN_CREATE | IN_MODIFY | IN_DELETE);
if (wd == -1) {
printf("Couldn't add watch to %s. errno=%d\n", argv[1], errno);
return -1;
} else {
printf("Watching:: %s\n",argv[1]);
}
/* do it forever*/
while (1) {
i = 0;
length = read(fd, buffer, BUF_LEN);
if (length < 0) {
perror("read");
}
while (i < length) {
struct inotify_event *event = (struct inotify_event *) &buffer[i];
if (event->len) {
if (event->mask & IN_CREATE) {
printf("Create event. file=%s, wf=%d\n", event->name, event->wd);
}
if (event->mask & IN_MODIFY) {
printf("Modify event. file=%s, wf=%d\n", event->name, event->wd);
}
if (event->mask & IN_DELETE) {
printf("Delete event. file=%s, wf=%d\n", event->name, event->wd);
}
i += EVENT_SIZE + event->len;
}
}
}
/* Clean up*/
inotify_rm_watch(fd, wd);
close(fd);
return 0;
}

Answer 1

If you want to monitor the creation of file/directory, you should watch the parent directory since the new file/directory does not exist when you calls inotify_add_watch().
Then when any file/directory is created in your watching directory, you will get a event, and the new file/direcotry name will be in event->name.