PHP - Manual: key

2024-11-23

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key

(PHP 4, PHP 5, PHP 7, PHP 8)

key — 从关联数组中取得键名

说明

key(array|object $array): int|string|null

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。

更新日志

版本	说明
8.1.0	弃用在 object 上调用此函数。在 object 优先使用 get_mangled_object_vars() 或者使用 ArrayIterator。

范例

示例 #1 key() 例子


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

// 此循环将会输出数组中所有值等于 “apple” 的键（key）
while ($fruit_name = current($array)) {
    if ($fruit_name == 'apple') {
        echo key($array), "\n";
    }
    next($array);
}
?>

以上例程会输出：

fruit1
fruit4
fruit5

参见

current() - 返回数组中的当前值
next() - 将数组中的内部指针向前移动一位
array_key_first() - 获取指定数组的第一个键
foreach

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User Contributed Notes 5 notes

down

380

lhardie ¶

8 years 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.

down

vinob44 at gmail dot com ¶

8 years 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
?>

down

FatBat ¶

10 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.
?>

down

Md Tahazzot ¶

2 years ago


(Editor note: Or just use the array_keys function)


Make as simple as possible but not simpler like this one :)


$k = array();

for($i = 0; $i < count($arr); $i++){

    $k[$i] = key($arr);

    next($arr);

}

down

-9

danielmadsv at gmail dot com ¶

3 years ago


In addition to FatBat's response, if you'd like to find out the highest key in an array (assoc or not) but don't want to arsort() it, take a look at this:

<?php

$arr = [ '3' => 14, '1' => 15, '4' => 92, '15' => 65 ];

$key_of_max = array_search( max($arr) , $arr);

?>

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官方地址：https://www.php.net/manual/en/function.key.php

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PHP官方手册 - 互联网笔记

key

说明

参数

返回值

更新日志

范例

参见

User Contributed Notes 5 notes