What does null value mean in PHP

1: What does the null value mean?

NULL is a special mark in php. The NULL value means that a variable has no value. NULL The only possible value of the type is NULL.

A variable is considered NULL under the following circumstances:

1. It is assigned a value of NULL.

2. It has not been assigned a value.

3. Be unset().

2: Syntax

The NULL type has only one value, which is the case-insensitive constant NULL.

<?php
$var = NULL;       
?>

is_null ( mixed $var ) : bool

Returns TRUE if var is null, otherwise returns FALSE.

Look at the NULL type to know when a variable is considered NULL.

Three: Converting to NULL

Using (unset) $var Converting a variable to null will not delete the variable or unset its value. Just returns a NULL value.

Note: Empty arrays are converted to null via non-strict equality '==' comparisons. If it is possible to get an empty array, use is_null() or '==='.

$a = array();
$a == null  <== return true
$a === null < == return false
is_null($a) <== return false

NULL should represent no value and not be considered the value itself.

NULL is a null bit, this is missing information, talking about "null value" is a semantic awkwardness, but if a variable can exist without a value, then the language and implementation must have something to represent this situation.

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