isset() vs array_key_exists()

isset() : 

Determine if a variable is set and is not NULL. 

If a variable has been unset with unset(), it will no longer be set. isset() will return FALSE if testing a variable that has been set to NULL. Also note that a NULL byte ("\0") is not equivalent to the PHP NULL constant.

If multiple parameters are supplied then isset() will return TRUE only if all of the parameters are set. Evaluation goes from left to right and stops as soon as an unset variable is encountered. 

array_key_exists() :

Checks if the given key or index exists in the array. array_key_exists() returns TRUE if the given key is set in the array. key can be any value possible for an array index.

Example:

$a =array (‘language’ => ‘PHP’, ‘author’ => null);

isset($a['language']);                      // true
array_key_exists('language', $a);  // true

isset($a['author']);                        // false
array_key_exists('author', $a);    // true

So in case of array_key_exists() null is also a value.

Performance :

isset() is significantly faster than array_key_exists(). Check the following example.

<?php

$a = array('language' => 'PHP', 'author' => null);

$start_time = microtime(true);

             for ($i = 0; $i < 1000000; $i++) {

                         if (array_key_exists('blog', $a) && $foo['blog'] === 'dirtyhandsphp') {

                                    echo "Not here";

                        }

            }

            $end_time = microtime(true);

            echo "Time Taken by array_key_exists() : ".($end_time-$start_time)."\n";

            $start_time = microtime(true);

            for ($i = 0; $i < 1000000; $i++) {

                        if (isset($foo['blog']) && $foo['blog'] === 'dirtyhandsphp') {

                                                echo "Not here";

                        }

            }

            $end_time = microtime(true);

            echo "<br>";

            echo "Time Taken by isset() : ".($end_time-$start_time);

?>

It gives me the following output:

Time Taken by array_key_exists() : 0.54193115234375
Time Taken by isset() : 0.13503885269165

Check yours.

It is said that isset() is 2.5 times faster than array_ket_exists() but out output shows that it’s around 4 times faster.

isset() is faster because it is a language construct; it does not suffer the overhead of a function call like array_key_exists() does. However, the two are not completely interchangeable. isset() also checks the value associated with the key, and will return false if that value is null. On the other hand, array_key_exists() only checks the key, and will return true for keys that point to a null value. Sometimes this distinction is important. So when you don’t need to distinguish the null value, please use isset().

Thanks!!!! Enjoy Programming :)