PHP 5.4.31 Released

key

(PHP 4, PHP 5)

key从关联数组中取得键名

说明

mixed key ( array &$array )

key() 返回数组中当前单元的键名。

参数

array

该数组。

返回值

key() 函数返回数组中内部指针指向的当前单元的键名。 但它不会移动指针。如果内部指针超过了元素列表尾部,或者数组是空的,key() 会返回 NULL

范例

Example #1 key() 例子

<?php
$array 
= array(
    
'fruit1' => 'apple',
    
'fruit2' => 'orange',
    
'fruit3' => 'grape',
    
'fruit4' => 'apple',
    
'fruit5' => 'apple');

// this cycle echoes all associative array
// key where value equals "apple"
while ($fruit_name current($array)) {
    if (
$fruit_name == 'apple') {
        echo 
key($array).'<br />';
    }
    
next($array);
}
?>

以上例程会输出:

fruit1<br />
fruit4<br />
fruit5<br />

参见

  • current() - 返回数组中的当前单元
  • next() - 将数组中的内部指针向前移动一位

add a note add a note

User Contributed Notes 6 notes

up
17
vinob44 at gmail dot com
9 months ago
Suppose if the array values are in numbers and numbers contains `0` then the loop will be terminated. To overcome this you can user like this

<?php
$array
= array(
   
'0' => '5',
   
'1' => '2',
   
'2' => '0',
   
'3' => '3',
   
'4' => '1');

// wrong approach

while ($fruit_name = current($array)) {

        echo
key($array).'<br />';
      
next($array);
}

// the way will be break loop when arra('2'=>0) because its value is '0', while(0) will terminate the loop

// correct approach
while ( ($fruit_name = current($array)) !== FALSE ) {

        echo
key($array).'<br />';
      
next($array);
}
//this will work properly
?>
up
9
lhardie
3 months ago
Note that using key($array) in a foreach loop may have unexpected results. 

When requiring the key inside a foreach loop, you should use:
foreach($array as $key => $value)

I was incorrectly using:
<?php
foreach($array as $value)
{
 
$mykey = key($array);
}
?>

and experiencing errors (the pointer of the array is already moved to the next item, so instead of getting the key for $value, you will get the key to the next value in the array)

CORRECT:
<?php
foreach($array as $key => $value)
{
 
$mykey = $key;
}

A noob error, but felt it might help someone else out there.
up
11
FatBat
2 years ago
Needed to get the index of the max/highest value in an assoc array.
max() only returned the value, no index, so I did this instead.

<?php
reset
($x);   // optional.
arsort($x);
$key_of_max = key($x);   // returns the index.
?>
up
-6
yarco dot w at gmail dot com
6 years ago
Re: br_joris[at]hotmail[doth]com

Do you really mean you want 2 keys point to 1 value?
What you've written seems you want 1 key point to 2 values.

But if you really want 2 keys point to 1 value, you could do the following:

<?php
$buf
['key1'] = 'abc';
$buf['key2'] = & $buf['key1'];
?>
up
-13
goker.cebeci
2 years ago
object usage:

<?php

$object
= new stdClass();
$object->child->key = 'value';

echo
key((array) $object->child);
// key

?>
up
-14
michael
5 years ago
Here is an improved version of the KeyName function below. It is simpler and faster, especially on large arrays as it runs in O(1) instead of O(n).

<?php
function KeyName(array $a, $pos) {
   
$temp = array_slice($a, $pos, 1, true);
    return
key($temp);
}
?>

Also, KeyName($a, -1) will return the last key, etc.
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