Common ways to determine whether an array is empty in PHP (five methods)

This article introduces the array problems encountered in PHP development. The editor here summarizes 5 methods for determining whether the array is empty in PHP. Friends who need it can refer to it.

This article introduces PHP For array problems encountered in development, here are 5 methods to determine whether a PHP array is empty. Friends in need can refer to it.

1. isset function: determine whether the variable has been initialized

Note: It does not determine whether the variable is empty, and can be used to determine whether the elements in the array have been defined

Note: When using isset to determine whether an array element has been initialized, its efficiency is about 4 times higher than array_key_exists

<?php
$a = '';
$a['c'] = '';
if (!isset($a)) echo '$a 未被初始化' . "";
if (!isset($b)) echo '$b 未被初始化' . "";
if (isset($a['c'])) echo '$a 已经被初始化' . "";
// 显示结果为
// $b 未被初始化
// $a 已经被初始化

2. empty function: detection Whether the variable is "empty"

Explanation: Any uninitialized variable, a variable with a value of 0 or false or an empty string "" or null, an empty array, or an object without any attributes will be judged as empty==true

Note 1: Uninitialized variables can also be detected as "empty" by empty

Note 2: empty can only detect variables, not statements

<?php
$a = 0;
$b = '';
$c = array();
if (empty($a)) echo '$a 为空' . "";
if (empty($b)) echo '$b 为空' . "";
if (empty($c)) echo '$c 为空' . "";
if (empty($d)) echo '$d 为空' . "";

3. var == null Function: Determine whether the variable is "empty"

Description: The value is 0 or false or the empty string "" or null Variables and empty arrays will be judged as null

Note: The significant difference from empty is that var == null will report an error when the variable is not initialized.

<?php
$a = 0;
$b = array();
if ($a == null) echo '$a 为空' . "";
if ($b == null) echo '$b 为空' . "";
if ($c == null) echo '$b 为空' . "";
// 显示结果为
// $a 为空
// $b 为空
// Undefined variable: c

4. is_null function: detect whether the variable is "null"

Description: When the variable is assigned a value of "null", detect The result is true

Note 1: null is not case-sensitive: $a = null; $a = NULL makes no difference

Note 2: Only when the value of the variable is "null", Only when the detection result is true, 0, empty string, false, and empty array are all detected as false

Note 3: When the variable is not initialized, the program will report an error

<?php
$a = null;
$b = false;
if (is_null($a)) echo '$a 为NULL' . "";
if (is_null($b)) echo '$b 为NULL' . "";
if (is_null($c)) echo '$c 为NULL' . "";
// 显示结果为
// $a 为NULL
// Undefined variable: c

5. var === null Function: Detect whether the variable is "null", and the type of the variable must also be "null"

Description: When the variable is assigned a value of "null" When, at the same time, when the type of the variable is also "null", the detection result is true

Note 1: When it is judged to be "null", it is equal to the same effect as is_null

Note 2: Variable When not initialized, the program will report an error

Summary:

In PHP, "NULL" and "empty" are two concepts.

isset is mainly used to determine whether a variable has been initialized.

empty can set variables with values ​​of "false", "empty", "0", "NULL" and "uninitialized". Judged as TRUE

is_null Only variables whose value is "NULL" are judged as TRUE

var == null Judged as "false", "empty", "0", "NULL" All variables are judged to be TRUE

var === null. Only variables with a value of "NULL" are judged to be TRUE

. Note: When judging whether a variable is really "NULL", most of the Use is_null to avoid interference with values ​​such as "false" and "0".

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