How to check null values ​​using PHP (4 methods)

In the previous article "PHP Array Learning: How to Remove Blank or Duplicate Elements", we learned that we can use the empty() function to determine whether a value is empty. So what are the ways to check null values ​​in PHP? This time we will learn about several common methods. If you need it, you can learn about it~

The theme of today’s article is: using PHP to detect whether a value is empty or not. Okay, let’s get straight to the point. Here are some common methods.

Method 1: Use empty()

empty function: detect whether the variable is "empty"

Any uninitialized variable, the value is 0 or false or empty string "" or null variables, empty arrays, objects without any attributes will be judged as TRUE.

Let’s take a closer look at the code example:

<?php
$a = &#39;test&#39;;
$b = array(&#39;key1&#39; => &#39;value1&#39;);
$class = new stdClass();

var_dump(empty($c)); // 输出 bool(true)
var_dump(empty($b[&#39;key2&#39;])); // 输出 bool(true)
var_dump(empty($class)); // 输出 bool(false)
var_dump(empty($class->test->test)); // 输出 bool(true)


class EmptyClass{};
$empty_class = new EmptyClass();
var_dump(empty($empty_class));// 输出 bool(false)
?>

Output result:

The following variables will be considered empty Is empty:

• "" (empty string)

• 0 (0 as an integer)

• 0.0 (0 as a floating point number)

• "0" (0 as a string)

• NULL

• FALSE

• array() (an empty array)

• $var; (one declared, But variables with no value)

Learn about0,'0','', null、falseThe difference between these five types.

• null means non-existence: the value is not stored in the zval space at the bottom of PHP, only a type mark IS_NULL is stored.

• And 0, '0', '', false these four exist, the bottom layer of php is to open up zval space storage, with value and type.

• string '0' is not equal to string ''

• int 0 is equal to string '' null, (non-identical comparison, PHP will do type conversion)

• string '0' is not equal to null, int 0 is equal to null
  

Method 2: Use isset()

isset function: determine whether the variable has been initialized and can be used to test whether the variable has been configured. Returns true if the variable already exists; returns false otherwise.

Let’s take a look at the code example below:

<?php
$a = &#39;test&#39;;
$b = array(&#39;key1&#39; => &#39;value1&#39;);
$class = new stdClass();

var_dump(isset($class->test->test)); // 判断对象属性是否定义：输出 bool(false)
var_dump(isset($a)); // 判断变量是否定义：输出 bool(true)
var_dump(isset($c)); // 判断变量是否定义：输出 bool(false)
var_dump(isset($b[&#39;key1&#39;])); // 判断数组元素是否定义：输出 bool(true)
var_dump(isset($b[&#39;key2&#39;])); // 判断数组元素是否定义：输出 bool(false)
?>

Output result:

Method 3: Use is_null()

is_null function: detect whether the variable is "null".

When a variable is assigned a value of "null", the detection result is true; 0, empty string, false, and empty array are all detected as false.

Let’s take a closer look at the code example:

<?php
$a = null;
$b = false;
var_dump(is_null($a));   
var_dump(is_null($b));  
var_dump(is_null($c)); 
?>

Output result:

Method 4: Use == or === operator

• can use var == null to determine whether the variable is "null". When a variable is assigned a value of "null", the detection result is true; while 0, empty string, false, and empty array are all detected as false. If the variable is not initialized, the program will report an error.

The essence is that the == expression will perform automatic type conversion on the variables on both sides, so the judgment result is true.

Let’s take a look at the code example below:

<?php
$a = 0;
$b = array();
var_dump($a == null);   
var_dump($b == null);  
var_dump($c == null); 
?>

• ##You can use

  var === null To detect whether the variable is "null", the type of the variable must also be "null". When judging "null", equal to is_null has the same effect.

<?php
$a = 0;
$b = false;
$c = 0.0;
$d = null;
$e = &#39;&#39;;
var_dump(0 === $a);   // 输出 bool(true)
var_dump(0 === $b);  // 输出 bool(false)
var_dump(0 === $c); // 输出 bool(false)
var_dump(0 === $d);  // 输出 bool(false)
var_dump(0 === $e);   // 输出 bool(false)
var_dump(&#39;&#39; === $e);  // 输出 bool(true)
var_dump(&#39;&#39; === $a);  // 输出 bool(false)
var_dump(&#39;&#39; === $b);  // 输出 bool(false)
var_dump(0.0 === $c);// 输出 bool(true)
var_dump(0.0 === $a);  // 输出 bool(false)
?>

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