PHP determines that it is not empty

empty() function: detect whether the variable is "empty"

Description: Any uninitialized variable, the value is 0 or false Or empty string "" or null variable, empty array, object without any attributes, empty(variable) == 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, not statements.

<?php
$a = 0;
$b = &#39;&#39;;
$c = array();
if (empty($a)) echo &#39;$a 为空&#39; . "<br/>";
if (empty($b)) echo &#39;$b 为空&#39; . "<br/>";
if (empty($c)) echo &#39;$c 为空&#39; . "<br/>";
if (empty($d)) echo &#39;$d 为空&#39; . "<br/>";
//结果
// $a 为空
// $b 为空
// $c 为空
// $d 为空
var_dump(empty(null));
var_dump(empty(0));
var_dump(empty(&#39;&#39;));
var_dump(empty([]));
//结果
// bool(true)
// bool(true)
// bool(true)
// bool(true)

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

Description: A variable whose value is 0 or false or an empty string "" or null, 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.

is_null Function: Detect whether the variable is "null"

Description: 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;a = NULL makes no difference.

Note 2: Only when the value of the variable 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.

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