Null (PHP)

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Set a variable to null

[1]:

$x = null;

Check for null + variations

is_null()

Gewoon: is_null() [2]:

$myvar = NULL; is_null($myvar);  // True
$myvar = 0; is_null($myvar);     // False
$myvar = FALSE; is_null($myvar); // False
$myvar = '';  is_null($myvar);   // False
is_null($some_undefined_var);    // True, but the script throws a notice because $some_undefined_var doesn't exist

isset()

[3]:

The function isset() checks whether a variable is defined (a.k.a exists) within your script. However, isset() also sees variables that have the null value as being not set (if you take the function wording literally).

This can be a little confusing but a few examples will show you exactly what I mean:

$myvar = NULL; isset($myvar);  // False
$myvar = 0; isset($myvar);     // True
$myvar = FALSE; isset($myvar); // True
$myvar = '';  isset($myvar);   // True
isset($some_undefined_var);    // False

empty()

The function empty() checks whether a variable evaluates to what PHP sees as a "falsy"(a.k.a empty) value. This being said, a variable is empty if it's undefined, null, false, 0 or an empty string.

To better understand the way empty works... you should think about this function as being the same as: !isset($var) || $var==false. Examples:

$myvar = NULL; empty($myvar);  // True
$myvar = 0; empty($myvar);     // True
$myvar = FALSE; empty($myvar); // True
$myvar = '';  empty($myvar);   // True
empty($some_undefined_var);    // True

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