Detailed introduction to determining whether a variable is empty in PHP_PHP Tutorial

There are many ways to judge whether a variable is empty in PHP. PHP provides us with empty, isset, var == null, is_null and other functions to judge variables. Let me share with you how to use these methods. .

A simple comparison of empty() and isset().

The code is as follows

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代码如下	复制代码
$var = 0; // 结果为 true，因为 $var 为空         // 结果为 true，因为 $var =0         if (empty($var)) { echo '$var is either 0 or not set at all'; }         //结果为false， 因为$var已经设置了         if (!isset($var)) { echo '$var is not set at all'; }  ?>

           $var = 0; // The result is true because $var is empty                 // The result is true because $var =0

If (empty($var)) { echo '$var is either 0 or not set at all'; }

​​​​ //The result is false because $var has been set

If (!isset($var)) { echo '$var is not set at all'; }
?>

Objects judged by empty and isset above to have no attributes will be considered empty.

var == null

代码如下	复制代码
$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

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 that var == null will report an error when the variable is not initialized.

代码如下	复制代码
$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 变量==0 或 变量===0

The code is as follows

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代码如下	复制代码
$a ===0  $a ==="" $a ==0 等于 $a ==""

$a = 0;

$b = array(); if ($a == null) echo '$a is empty' . ""; if ($b == null) echo '$b is empty' . "";

if ($c == null) echo '$b is empty' . "";

//Display the result as

// $a is empty

代码如下	复制代码
if(empty($id)) $id=1; // 若 id=0 ，id 也会为1 if(!isset($id)) $id=1; // 若 id=0 ，id 不会为1  可分开运行以下代码检测上述推断： if(empty($id)) $id=1;    print $id; // 得到 1  if(!isset($id)) $id=1;    print $id; //得到 0

// $b is empty // Undefined variable: c

is_null

The code is as follows	Copy code
$a = null; $b = false; if (is_null($a)) echo '$a is NULL' . ""; if (is_null($b)) echo '$b is NULL' . ""; if (is_null($c)) echo '$c is NULL' . ""; //Display the result as // $a is NULL // Undefined variable: c Variable==0 or Variable==0

Example

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$a ===0 $a ==="" $a ==0 is equal to $a ==""

When passing parameters in php url When the URL tail parameter of the php page appears with id=0 (for example: test.php?id=0), try to compare:

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if(empty($id)) $id=1; // If id=0, id will also be 1 if(!isset($id)) $id=1; // If id=0, id will not be 1 The above inference can be detected by running the following code separately: if(empty($id)) $id=1; Print $id; // get 1 if(!isset($id)) $id=1; Print $id; //get 0

Summary

NULL and empty are two different concepts in php,

isset is mainly used to determine whether the variable has been initialized
empty can judge variables with values ​​of "false", "empty", "0", "NULL", and "uninitialized" as TRUE
is_null only evaluates variables with a value of “NULL” as TRUE
var == null Judges variables with values ​​of "false", "empty", "0", and "NULL" as TRUE
var === null Only variables with a value of "NULL" are judged as TRUE

Some other functions that may use PHP variable judgment

isset($ var): //Whether the variable has been declared

empty($ var): //Is the variable empty

defined($ var): //Is the constant defined? define()

is_array($ var): //Check whether the measured variable is an array

is_null($ var): //Check whether the measured variable is null

http://www.bkjia.com/PHPjc/628876.htmlwww.bkjia.comtruehttp: //www.bkjia.com/PHPjc/628876.htmlTechArticleWe have many ways to determine whether a variable is empty in PHP. PHP provides us with empty,isset,var = = null, is_null and other functions to judge variables. Let me share these methods with you...