Essential Books

Null

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PHP represents “no value” with the null keyword. It’s somewhat similar to the null pointer in C-language and to the NULL value in SQL.

Setting the variable to null: 

$nullvar = null; // directly

function doSomething() {} // this function does not return anything
$nullvar = doSomething(); // so the null is assigned to $nullvar

Checking if the variable was set to null: 

if (is_null($nullvar)) { /* variable is null */ }

if ($nullvar === null) {  /* variable is null */ }

Null vs undefined variable

If the variable was not defined or was unset then any tests against the null will be successful but they will also generate a Notice: Undefined variable: nullvar: 

$nullvar = null;
unset($nullvar);
if ($nullvar === null) {  /* true but also a Notice is printed */ }
if (is_null($nullvar)) {  /* true but also a Notice is printed */ }

Therefore undefined values must be checked with isset: 

if (!isset($nullvar)) {  /* variable is null or is not even defined */  }
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Types:
* Types
* Type Comparison
* Boolean
* Float
* Strings
* Callable
* Null
* Type Casting
* Resources
* Type Juggling
* Integers
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0 Getting started
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