Returns the user ID of the owner of the file, or FALSE in case of an error. The user ID is returned in numerical format, use posix_getpwuid() to resolve it to a username.
The results of this function are cached. See clearstatcache() for more details.
This function will not work on remote files; the file to be examined must be accessible via the server's filesystem.
Note: This function is not implemented on Windows platforms.