5 ways to determine whether an array is empty in PHP

In PHP, "NULL" and "empty" are two concepts.
isset is mainly used to determine whether a variable has been initialized.
empty can judge variables with values ​​of "false", "empty", "0", "NULL" and "uninitialized" as TRUE.
is_null can only judge variables with values ​​of " NULL" variables are judged as TRUE
var == null Variables with values ​​​​"false", "empty", "0", and "NULL" are all judged as TRUE
var === null Only variables with values ​​​​are "NULL" The variable is judged to be TRUE
Note: When judging whether a variable is really "NULL", is_null is mostly used to avoid interference from "false", "0" and other values.