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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 is initialized
Note: It does not determine whether the variable is empty, and can be used to determine whether the elements in the array are initialized. 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: detect whether the variable is "empty"
Description: Any uninitialized variable, value 0 or false or empty string "" or null variable, 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 = ''; $c = array(); if (empty($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"
Note: Variables and empty arrays whose value is 0 or false or empty string "" or null will be judged as null
Note: The significant difference from empty is: when the variable is not initialized, var = = null will report an error.
<?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 When "null", the detection result is true
Note 1: null is not case-sensitive: $a = null; $a = NULL makes no difference
Note 2: Only the value of the variable When it is "null", 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"
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 judged as "null", it is equal to is_null The effect is the same
Note 2: When the variable is 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".
The above is the entire content of this article, I hope it will be helpful to everyone's study.
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