php array_key_exists, !empty and isset fails for no reason?

问题

php 7.0.8 on ubuntu 16.0.4 LTS could somebody give me a hint why an array key check would fail when the key clearly exists, program execution just stops, with no explanation even with all error reporting enabled.

The data type held in the array element is a string containing a torrent file downloaded from fedora website https://torrents.fedoraproject.org/

other functions fail here aswell such as !empty on the array key

the key in this instance is 0

if(array_key_exists($index, $this->_webpage)){
            return $this->_webpage[$index];
        }else{
            /* throw notice */
            trigger_error("Array index is out of range. Can not get webpage.", E_USER_NOTICE);
            return FALSE;
        }

NOTE: iv been using this same function to check that webpages have been downloaded and it worked on the same system, im just adding torrent parsing to my application

回答1:

SUMMARY array_key_exists will definitely tell you if a key exists in an array, whereas isset will only return true if the key/variable exists and is not null and empty return true if the variable is an empty string, false, array(), NULL, “0?, 0, and an unset variable

More details

isset()

From PHP manual – isset():

isset — Determine if a variable is set and is not NULL

In other words, it returns true only when the variable is not null.

empty()

From PHP Manual – empty():

empty — Determine whether a variable is empty

In other words, it will return true if the variable is an empty string, false, array(), NULL, “0?, 0, and an unset variable.

Also empty() does not generate a warning if the variable does not exist.

array_key_exists

From PHP Manual – array_key_exists():