BE_USER_LOGGED_IN where can i get this true.

For example : code line from comments module, comment.php

Code:

---

// Get all published comments
$objCommentsStmt = $this->Database->prepare("SELECT * FROM tl_comments WHERE source=? AND parent=?" . (!BE_USER_LOGGED_IN ? " AND published=1" : "") . " ORDER BY date" . (($objConfig->order == 'descending') ? " DESC" : ""));

---

Here I am expecting, when I am logged in as a BE user (in my case as admin), I am able to see all the comments of an Article in FE (of course in same browser session) irrespective of published or not. Am I right?
Since I am not seeing any comments unless I publish it, I assume I didn't understand the constant BE_USER_LOGGED_IN or doing something wrong. Any hinweis would be great.

BE_USER_LOGGED_IN is to tell you if you have a backend user logged in, similarily FE_USER_LOGGED_IN will return if you have a frontend user logged in.
It will not tell you which user is logged in.

yes but you forget that comments also have MODERATION. You might have turned on moderation, then you have to approve the comment before its visible....

As far as I experienced, BE_USER_LOGGED_IN is 'true' in the frontend, only when you are previewing the site while showing disabled items.

Yeah FloB is right. There is a drop-down menu in the preview mode that allows you to set this on/off. The new TL doesn't anymore show unpublished items by default... that was removed in favour of the new preview yellow bar...