array_key_exists

http://jp2.php.net/manual/ja/function.array-key-exists.php

array_key_existsとisset

$array = array('hoge' => null);
var_dump(array_key_exists('hoge', $array)); // true
var_dump(isset($array['hoge']));            // false

benchmark

issetの方が３倍ほど早い

$array = array('hoge' => null);
require_once('Benchmark/Timer.php');
$b = new Benchmark_Timer();
$b->start();
for($i = 0; $i < 100000; $i++){
array_key_exists('hoge', $array); // true
}
$b->setMarker(1);
for($i = 0; $i < 100000; $i++){
isset($array['hoge']); // false
}

$b->display();

----------------------------------------------------
marker  time index            ex time         perct   
----------------------------------------------------
Start   1179177790.06100900   -                0.00%
----------------------------------------------------
1       1179177790.20730100   0.146292        77.16%
----------------------------------------------------
Stop    1179177790.25059300   0.043292        22.84%
----------------------------------------------------
total   -                     0.189584       100.00%
----------------------------------------------------