Detailed examples of the differences between empty, isset and isnull in php

empty

If the variable is a non-empty or non-zero value, empty() returns FALSE. In other words, "", 0, "0", NULL, FALSE, array(), var $var, undefined; and objects without any attributes will be considered empty, and TRUE will be returned if var is empty. .

Code example:

$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' . "";
// 以上输出皆为空

isset (Online learning video tutorial sharing: php video tutorial)

If the variable exists ( non-NULL), returns TRUE, otherwise returns FALSE (including undefined). The variable value is set to: null, and the return value is also false; after unsetting a variable, the variable is canceled. Note that isset handles NULL value variables specially.

Code example:

$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

is_null

Detect whether the incoming value [value, variable, expression] is null, only one variable is defined , and its value is null, it returns TRUE. Others return FALSE [An error will occur after undefined variables are passed in! 】

Code example:

$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

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