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I've seen a lot of people do the former, is there any performance benefit doing one vs the other? Or is it just an eye candy? I personally use the latter every time as it is shorter and personally more readable to me.

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Note, both statements are not equal. If $array[$key] is "" or 0, it is empty but the key still exists. – Jens Struwe Jul 30 '11 at 16:58
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4 Answers

up vote 0 down vote accepted

The other responses focus on the differences between the two functions. This is true, but if the source array does not contain null or 0 or "", ... (empty values) values you can benchmark the speed of the two functions:

<?php

function makeRandomArray( $length ) {
    $array = array();
    for ($i = 0; $i < $length; $i++) {
        $array[$i] = rand(1, $length);
    }

    return $array;
}

function benchmark( $count, $function ) {
    $start = microtime(true);
    for ($i = 0; $i < $count; $i++) {
        $function();
    }
    return microtime(true) - $start;
}

$runs = 100000;
$smallLength = 10;
$small = makeRandomArray($smallLength);

var_dump(benchmark($runs, function() {
    global $small, $smallLength;
    array_key_exists(rand(0, $smallLength), $small);
}));
var_dump(benchmark($runs, function() {
    global $small, $smallLength;
    !empty($small[rand(0, $smallLength)]);
}));

Which gave me the following results:

For a small array:

  • array_key_exists: float(0.18357992172241)
  • empty: float(0.072798013687134)
  • isset: float(0.070242881774902)

For a relative big array:

  • array_key_exists: float(0.57489585876465)
  • empty: float(0.0068421363830566)
  • isset: float(0.0069410800933838)

So if it's possible it's faster to use empty or isset.

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try running the same test on isset(). – Salman A Jul 30 '11 at 17:16
@Salman I updated the answer. – KARASZI István Jul 30 '11 at 17:21
interesting stats, thanks. I thought isset() was the fastest but seems like its performance is equivalent to that of empty. – Salman A Aug 1 '11 at 5:25
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up vote 0 down vote

empty($array[$key]) returns true when the value of $array[$key] is empty; empty means "", 0, NULL, FALSE etc etc etc. Note that these values may actually make sense in your code.

array_key_exists($key, $array) returns true when the specified key exists in the array. It does not consider the value of $array[$key].

A much faster alternative to check whether a key exists in an array is to use isset($array[$key]).

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up vote 0 down vote

They both are different

array_key_exists($key, $array) checks whether the key exist in the array and returns TRUE if the given key is set in the array.

whereas

!empty($array[$key]) Determine whether a variable value is empty or not

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up vote 5 down vote 
$array = array(
    'foo' => null
);

echo (int)!empty($array['foo']); // 0
echo (int)array_key_exists('foo', $array); // 1
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Same applies to isset: isset($array['foo']) will yield false. – Gumbo Jul 30 '11 at 17:05
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