How to determine if an array is empty in php

Judgment method: 1. Use the isset() function to determine whether the elements in the array have been defined. If not, it will be an empty array; 2. Use the empty() function to check whether the array variable is empty. If it is empty, then It is an empty array; 3. Use "array variable == null" to determine whether the array variable is "empty". If it is empty, it is an empty array.

The operating environment of this tutorial: windows7 system, PHP7.1 version, DELL G3 computer

PHP Determine whether it is 5 methods of empty array

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

Explanation: It does not It will 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 the array elements have been initialized, its efficiency is about 4 times higher than array_key_exists

<?php
$a = &#39;&#39;;
$a[&#39;c&#39;] = &#39;&#39;;
if (!isset($a)) echo &#39;$a 未被初始化&#39; . "";
if (!isset($b)) echo &#39;$b 未被初始化&#39; . "";
if (isset($a[&#39;c&#39;])) echo &#39;$a 已经被初始化&#39; . "";
// 显示结果为
// $b 未被初始化
// $a 已经被初始化

2. empty function: detect whether the variable is "empty"

Description: Any uninitialized variable, value is 0 or false or empty string "" Or null variables, empty arrays, and objects 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, but not statements

<?php
$a = 0;
$b = &#39;&#39;;
$c = array();
if (empty($a)) echo &#39;$a 为空&#39; . "";
if (empty($b)) echo &#39;$b 为空&#39; . "";
if (empty($c)) echo &#39;$c 为空&#39; . "";
if (empty($d)) echo &#39;$d 为空&#39; . "";

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

Description: Value Variables and empty arrays that are 0 or false or empty string "" or null 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 &#39;$a 为空&#39; . "";
if ($b == null) echo &#39;$b 为空&#39; . "";
if ($c == null) echo &#39;$b 为空&#39; . "";
// 显示结果为
// $a 为空
// $b 为空
// Undefined variable: c

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

Note: When the variable is assigned a value of "null", the detection result is true

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

Note 2: The detection result is true only when the value of the variable is "null". 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 &#39;$a 为NULL&#39; . "";
if (is_null($b)) echo &#39;$b 为NULL&#39; . "";
if (is_null($c)) echo &#39;$c 为NULL&#39; . "";
// 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"

Note: When a variable is assigned a value of "null" and the type of the variable is also "null", the detection result is true

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

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

Summary:

In PHP, "NULL" and "empty" are 2 a concept.

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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