What values are == NULL but not === NULL in PHP?

Question

Possible Duplicate:
Null vs. False vs. 0
How does php cast boolean variables?

I know that some values will return true for $value == NULL and not for $value === NULL but is there a complete list of these values?

Also, is isset($value) equivalent to $value === NULL and empty($value) equivalent to $value == NULL?

Maybe this will answer you http://php.net/manual/en/types.comparisons.php — nikc.org, Dec 20 '11 at 15:51
The only time when `$value === NULL` is true, is when `$value = NULL`, or it isn't defined. — BoltClock, Dec 20 '11 at 15:51
Neither of the Duplicate questions address types other than boolean or integer. For example array() == NULL vs. array() !== NULL. I was looking for a more complete list than those provided. — CLo, Dec 20 '11 at 16:06

score 3 · Accepted Answer · answered Dec 20 '11 at 15:51

3

http://www.php.net/manual/en/types.comparisons.php

answered Dec 20 '11 at 15:51

Your Common Sense

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Matthew · Answer 2 · 2011-12-20T16:03:20.800

1

NULL === NULL

Nothing else does. So if a function returns NULL then checking with === will return true.

Also, is isset($value) equivalent to $value === NULL and empty($value) equivalent to $value == NULL?

No, not strictly. Those two are "language constructs" and not functions. They only accept variable names, isset accepts multiple parameters, and warnings are relaxed when using unset variables.

edited Dec 20 '11 at 16:03

answered Dec 20 '11 at 15:51

Matthew

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score 0 · Answer 3 · answered Dec 20 '11 at 15:51

The purpose of the triple equals is to ensure the types match as well. Using only ==, PHP performs truthy/falsy logic, meaning 0==null, 0=='', null=='' are all true, but 0===null, 0==='', null==='' are all false.

Also, '90210'==90210 is true, but '90210'===90210 is false.

score 0 · Answer 4 · answered Dec 20 '11 at 15:52

I suggest you these readings:

About NULL: http://php.net/manual/en/language.types.null.php
About empty(): http://php.net/manual/en/function.empty.php (you are wrong about it!)
About isset(): http://php.net/manual/en/function.isset.php

From the offical documentation, they are very explanatory.

score 0 · Answer 5 · answered Dec 20 '11 at 15:54

Anything that evaluates to FALSE when converted to a boolean is == NULL.

So that would be:

  (bool) FALSE
   (int) 0
 (float) 0.0
(string) '' // an empty string
(string) '0'
 (array) array()
 // An object with zero member variables (PHP 4 only)
 // SimpleXML objects created from empty tags

And, obviously, NULL itself. But only NULL and variables with no value are === NULL.

This may help clarify some things.

What values are == NULL but not === NULL in PHP?

5 Answers5