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# array_keys

(PHP 4 , PHP 5)

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.

示範 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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