   #PHP Manual Array Functions array_key_exists array_map

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                                  array_keys

   (PHP 4 )
   array_keys -- Return all the keys of an array

Description

   array array_keys ( array input [, mixed search_value])

   array_keys() returns the keys, numeric and string, from the input
   array.

   If the optional search_value is specified, then only the keys for that
   value are returned. Otherwise, all the keys from the input are
   returned.

   Example 1. array_keys() example
   <?php
   $array = array(0 => 100, "color" => "red");
   print_r(array_keys($array));
   $array = array("blue", "red", "green", "blue", "blue");
   print_r(array_keys($array, "blue"));
   $array = array("color" => array("blue", "red", "green"),
                  "size"  => array("small", "medium", "large"));
   print_r(array_keys($array));
   ?>

   The printout of the program above will be:
Array
(
    [0] => 0
    [1] => color
)
Array
(
    [0] => 0
    [1] => 3
    [2] => 4
)
Array
(
    [0] => color
    [1] => size
)

   See also array_values() and array_key_exists().
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