PHP: if (!$val) VS if (empty($val)). Is there any difference?

Question

I was wondering what's the difference the two cases below, and which one is recommended?

$val = 0;

if (!$val) {
  //True
}

if (empty($val) {
  //It's also True
}

Solution 1

Have a look at the PHP type comparison table.

If you check the table, you'll notice that for all cases, empty($x) is the same as !$x. So it comes down to handling uninitialised variables. !$x creates an E_NOTICE, whereas empty($x) does not.

Solution 2

If you use empty and the variable was never set/created, no warning/error will be thrown.

Solution 3

Let see:

empty documentation:

The following things are considered to be empty:

• "" (an empty string)
• 0 (0 as an integer)
• 0.0 (0 as a float)
• "0" (0 as a string)
• NULL
• FALSE
• array() (an empty array)
• var $var; (a variable declared, but without a value in a class)

Booleans documentation:

When converting to boolean, the following values are considered FALSE:

• the boolean FALSE itself
• the integer 0 (zero)
• the float 0.0 (zero)
• the empty string, and the string "0"
• an array with zero elements
• an object with zero member variables (PHP 4 only)
• the special type NULL (including unset variables)
• SimpleXML objects created from empty tags

It seems the only difference (regarding the resulting value) is how a SimpleXML instance is handled. Everything else seems to give the same result (if you invert the boolean cast of course).

Comments

[rockerest]

+1. Also note that this is the same as != [boolean result of evaluating $val], so the last column of the first table is mostly what you should be looking at.

[Jason McCreary]

So what's the conclusion? From the list, boolean seems like the more robust check...

[Bachx]

Thanks, that's what I needed to know. So I guess empty($x) is the safer approach. I assume the difference is negligible performance wise right?

[xdazz]

Please note that when using empty() on inaccessible object properties, the __isset overloading method will be called, if declared.

[Mark Amery]

This is incorrect. A quick test at the PHP shell reveals that empty handles empty SimpleXMLElement instances just like ! does; it's simply an error in the empty documentation that they aren't mentioned there.

[leonbloy]

Gotta love the duplication of doc.