Q:

PHP: Does password_hash() check if the hash generated is unique? (Understanding!)

Simple question because i did not find a really helping answer on google: Does the password_hash() function also check if there is already such a hash generated for instance in the userdata file? 
I basically get what the function is doing, but i am fairly new to php, so i was not really able to see if the password is checked for uniqueness. 
Please be gentle on this noob question right here. I simply want to understand what i am using right there, and not only do it because my exercise sheet at university tells me so.

A:

No.
Two reasons:

the function will not know anything about "other" passwords.
You don't want this. What will you do if you hit a duplicate? Tell the user? He will then know someone's password. 

