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# array_key_exists

(PHP 4 >= 4.1.0, PHP 5)

array_key_exists -- Checks if the given key or index exists in the array

## Description

bool array_key_exists ( mixed key, array search )

array_key_exists() returns `TRUE` if the given key is set in the array. key can be any value possible for an array index. array_key_exists() also works on objects.

範例 1. array_key_exists() example

`<?php $search_array = array('first' => 1, 'second' => 4); if (array_key_exists('first', $search_array)) { echo "The 'first' element is in the array"; } ?>`

> 注: The name of this function is key_exists() in PHP 4.0.6.

範例 2. array_key_exists() vs isset()

isset() does not return `TRUE` for array keys that correspond to a `NULL` value, while array_key_exists() does.

`<?php $search_array = array('first' => null, 'second' => 4); // returns false isset($search_array['first']); // returns true array_key_exists('first', $search_array); ?>`

See also isset(), array_keys(), and in_array().

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