How to determine whether a variable is empty in php

empty function: detect whether the variable is "empty"

Description: Any uninitialized variable, the value is 0 or false or empty string "" or null variables, empty arrays, and objects without any attributes will be judged as empty==true (recommended learning: PHP Video Tutorial)

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

Note 2: empty can only detect variables, but not statements

$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' . "";

var == null function: Determine whether the variable is "empty"

Note: Variables and empty arrays with a value of 0 or false or an 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.

$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

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