Analyze the difference between empty(), isset() and is_null() in PHP

There has been a lot of discussion about the usage of empty(), isset() and is_null() functions of PHP, 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()

The 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, empty() will output true as long as the data type is empty or false.

isset()

Look at the output of isset:

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, 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 is literal.

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

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