How to use empty() in PHP to check whether a variable is empty

In the daily use of PHP, we often need to determine whether a variable is empty. PHP provides us with a built-in function empty() to help us check whether a variable is empty. First, let’s take a look at the syntax format:

Syntax:

empty  ( mixed $var )

• $var: Variables that need to be judged

• Return value: When a variable does not exist, or its value is equal to false, return true, otherwise return false.

PS: Before PHP 5.5, empty() only supported variables, and checking non-numeric string offsets would return true, PHP5.5 supports expressions.

Actual use:

1. Determine a variable that does not exist:

<?php
    var_dump(empty($a));
?>

输出：bool(true)

2. Determine a variable Unassigned variable:

<?php
$a;
var_dump(empty($a));
?>

输出：bool(true)

3. Judge the value of the variable to be equal to false:

<?php
$a="";//0、"0"、NULL、FALSE、 array()
var_dump(empty($a));
?>

输出：bool(true)

4. Use empty() on the string offset

<?php
$expected_array_got_string = &#39;somestring&#39;;
var_dump(empty($expected_array_got_string[&#39;some_key&#39;]));
var_dump(empty($expected_array_got_string[0]));
var_dump(empty($expected_array_got_string[&#39;0&#39;]));
var_dump(empty($expected_array_got_string[0.5]));
var_dump(empty($expected_array_got_string[&#39;0.5&#39;]));
var_dump(empty($expected_array_got_string[&#39;0 Mostel&#39;]));
?>

输出：
bool(true)
bool(false)
bool(false)
bool(false)
bool(true)
bool(true)

Recommendation: 《2021 PHP interview questions summary (collection)》《php video tutorial》

The above is the detailed content of How to use empty() in PHP to check whether a variable is empty. For more information, please follow other related articles on the PHP Chinese website!