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PHP - Manual: key

2024-03-28

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

add a noteadd a note

User Contributed Notes 5 notes

up
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.
up
59
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
?>
up
15
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.
?>
up
0
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);
}
up
-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);

?>

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

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