Introduction to the functions is_null, isset, empty in php

These three functions are easy to confuse in PHP, but they are often encountered during development and written interviews. Let’s summarize them here.

When the variable $a=null, the program result is

is_null($a) true

##isset($a )

false

empty($a)

true

Program result when variable $a=''(empty string) For

is_null($a)

false##isset($a)

trueempty($a)

true

When variable $a= ' ' (there is a space in the middle), the program result is

is_null($a)

false

isset($a)

true

empty($a)

false

When the variable $a=[] (empty array) the program result is

is_null($a)

false

##isset($a) true

empty($a) true

So we concluded:

1.is_null is only true for null and all others are false. In php, null is a variable that has neither type nor value.

2.isset is only false for null and the others are all t because '',' ', [], these three variables have clear data types, '' represents an empty string, ' ' represents a space string, [] represents an empty array. Therefore, a variable is true as long as it has type isset.

3.empty is false only for non-empty arrays and strings.

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