Diogo Oliveira de Melo

PHP: array_key_exists vs. isset

First, the basics. Let’s say you want to verify if $foo['bar'] is set. You can use either function:

array_key_exists('bar', $foo);
isset($foo['bar']);

The differences between those functions are:

1. array_key_exists is, as the name suggests, supposed to be used specifically for arrays, while isset can work with other var types as well;
2. isset does not return true if the array value is null (i.e.: if you have $foo['bar'] = NULL, array_key_exists($foo['bar']) will return true while isset($foo['bar']) will return false);
3. isset is MUCH FASTER than array_key_exists (about 5.6 x 1).

Below is the script to test all my claims:

<?php

$foo['bar'] = 'some value';

echo "Similar behaviour: " . PHP_EOL; 
var_dump(array_key_exists('bar', $foo)); // bool(true)
var_dump(isset($foo['bar']));            // bool(true)

echo "Differences:" . PHP_EOL;
echo "1. isset works with other variables, besides arrays." . PHP_EOL;
$foo = 'bar';
var_dump(isset($foo)); // bool(true)

echo "2. isset return false when value is null" . PHP_EOL;
$foo = array();
$foo['bar'] = null;
var_dump(isset($foo['bar'])); // bool(false)

echo "3. Speed" . PHP_EOL;

$i = 1000000;
$start = microtime(true);
while ($i--) {
    array_key_exists('bar', $foo);
}
$finish = microtime(true);
echo "array_key_exists: " . ($finish - $start) . " seconds " . PHP_EOL;

$i = 1000000;
$start = microtime(true);
while ($i--) {
    isset($foo['bar']);
}
$finish = microtime(true);
echo "isset: " . ($finish - $start) . " seconds " . PHP_EOL;

I am using PHP 5.6.13. When I ran that script on my computer, I got the following output:

Similar behaviour: 
bool(true)
bool(true)
Differences:
1. isset works with other variables, besides arrays.
bool(true)
2. isset return false when value is null
bool(false)
3. Speed
array_key_exists: 0.5188250541687 seconds 
isset: 0.092790126800537 seconds