The difference between php empty(), isset() and is_null()

There has been a lot of discussion about the usage of PHP's empty(), isset() and is_null() functions, and a lot of information may not be very clear. I repeat it here again, but instead of speaking from concepts, it should be more profound to memorize it by directly using program examples.

The types of tests are as follows:

<?php
 
$a;
$b = false;
$c = &#39;&#39;;
$d = 0;
$e = null;
$f = array();
 
?>

empty()

First is the var_dump output of empty:

<?php
 
var_dump(empty($a));
var_dump(empty($b));
var_dump(empty($c));
var_dump(empty($d));
var_dump(empty($e));
var_dump(empty($f));
 
?>

The program output is:

bool(true)
bool(true)
bool(true)
bool(true)
bool(true)
bool(true)

As can be seen from the code, as long as the data type is empty or false , empty() will output true.

isset()

Look at the output of isset again:

var_dump(isset($a));
var_dump(isset($b));
var_dump(isset($c));
var_dump(isset($d));
var_dump(isset($e));
var_dump(isset($f));
 
// 输出
bool(false)
bool(true)
bool(true)
bool(true)
bool(false)
bool(true)

It can be seen that isset() can only be used to determine whether it is NULL and undefined.

is_null()

Finally is the output of is_null:

var_dump(is_null($a));
var_dump(is_null($b));
var_dump(is_null($c));
var_dump(is_null($d));
var_dump(is_null($e));
var_dump(is_null($f));
 
// 输出
bool(true)
bool(false)
bool(false)
bool(false)
bool(true)
bool(false)

is_null literally means it.

It can be seen that empty() can be used to determine whether all data types are empty or false, while is_null is basically the same as isset and can only be used to determine whether it is NULL and undefined