数组 函数
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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。

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);
}
?>

参见 current() 和 next()。

数组 函数
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PHP手册 - N: 从关联数组中取得键名

用户评论:

HellFireAE at gmail dot com (17-Mar-2012 07:37)

I've used this as a way of getting $_GET's from the URL. It's actually quite cool, I don't know if this is a hack or what but I like it.

<?php
  switch(strToLower(key($_GET))){
    case "register":
      $page->set("{PAGE_TITLE}", "Register");
      break;
    default:
      $page->set("{PAGE_TITLE}", "Play");
      break;
  }
?>

So if you put "?register" it outputs the page title to "Register" and if it isn't that, then it's "Play".

Hope this helps people.

goker.cebeci (24-Feb-2012 03:41)

object usage:

<?php

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

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

?>

FatBat (17-Oct-2011 08:20)

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.
?>

FokeyJoe (10-Mar-2011 02:10)

Just to illustrate the behaviour of the internal pointer when you add items. Adding to an array does not affect the internal pointer.

<?php
$a = array();
var_dump(key($a));  // null
$a[] = "jump";
var_dump(key($a));  // 0
$a[] = "lazy";
var_dump(key($a));  // 0
end($a);
var_dump(key($a));  // 1
$a[] = "fox";
var_dump(key($a));  // 1
?>

Dallas at ekkysoftware dot com (05-Mar-2010 05:32)

I had a problem when there are nulls in your data, such as:-

<?php
$row = array(  'first'=>'number', 'second'=>'letter', 'third'=>null, 'forth'=>'word');

while($value = current($row)){
    echo "\"".key($row)."\"";
    next($row);
}
?>

The problem is that current() returns the value 'null', but it isn't the end of the list. To get the correct results I used:-

<?php
foreach($row as $value){
    echo "\"".key($row)."\"";
    next($row);
}
?>

jamon at clearsightdesign dot com (19-Aug-2009 06:24)

I wrote a simple, yet powerful function for finding a key in an array relative to another key. This is very useful for finding the next key in an associative array if you know the current key, or any other arbitrary key relative to the current key.

This function does not use a foreach loop. I have not tested it for speed compared to a foreach loop. I would assume it's faster since it uses PHP's built in functions, but I could be wrong. I'd appreciate feedback on this.

- Jamon Holmgren

<?php
    // array_key_relative - Returns a key in an associative array relative to another key without using foreach. Very useful for finding previous key or finding next key in array, etc
    // - Written by Jamon Holmgren (www.jamonholmgren.com). Last revised 8/18/2009. Free for any use.
    // function array_key_relative(array $array, string $current_key, int $offset)
    function array_key_relative($array, $current_key, $offset = 1) {
        // create key map
        $keys = array_keys($array);
        // find current key
        $current_key_index = array_search($current_key, $keys);
        // return desired offset, if in array, or false if not
        if(isset($keys[$current_key_index + $offset])) {
            return $keys[$current_key_index + $offset];
        }
        return false;
    }
?>

Usage example:

<?php
    $test_array = array(
        "apple" => "Red, shiny fruit",
        "orange" => "Orange, dull, juicy fruit",
        "pear" => "Usually green and odd-shaped fruit",
        "banana" => "Long yellow fruit that monkeys like to eat",
        "cantelope" => "Larger than a grapefruit",
        "grapefruit" => "Kind of sour"
    );
   
    echo array_key_relative($test_array, "apple", 2); // outputs "pear"
    echo array_key_relative($test_array, "orange", -1); // outputs "apple" */

    $next_key = array_key_relative($test_array, "banana", 1); // Get the key after banana (cantelope)
    echo $test_array[$next_key]; // outputs "Larger than a grapefruit"
?>

michael (09-Dec-2008 07:19)

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.

Twey (15-Mar-2008 08:25)

As of PHP5, objects are passed by reference by default.

egingell at sisna dot com (02-Dec-2007 11:12)

What's the point of lines 14 and 25? $array is destroyed when the function returns. If you want this to work as written, change line 2 to this: (pass $array by reference instead of by value)
<?
function add_key ($value, &$array) // returns the key of the value added or existing already within the array
?>

>    danny at dannymendel dot com
>    12-Apr-2006 09:41
>    An auto incremental key value function, returning the key value:
>   
> 1    <?
> 2    function add_key ($value, $array) // returns the key of the value added or existing already within the array
> 3    {
> 4        if (is_array ($array))
> 5        {
> 6            if (!in_array ($value, $array))
> 7            {
> 8                ksort ($array);
> 9   
>10                end ($array);
>11   
>12                $key = key ($array) + 1;
>13   
>14                $array[$key] = $value;
>15            }
>16            else
>17            {
>18                $key = array_search ($value, $array);
>19            }
>20        }
>21        else
>22        {
>23            $key = 1;
>24   
>25            $array[$key] = $value;
>26        }
>27        return $key;
>28    }
>29    ?>

yarco dot w at gmail dot com (13-Sep-2007 09:45)

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'];
?>

danny at dannymendel dot com (12-Apr-2006 04:41)

An auto incremental key value function, returning the key value:

<?
function add_key ($value, $array) // returns the key of the value added or existing already within the array
{
    if (is_array ($array))
    {
        if (!in_array ($value, $array))
        {
            ksort ($array);

            end ($array);

            $key = key ($array) + 1;

            $array[$key] = $value;
        }
        else
        {
            $key = array_search ($value, $array);
        }
    }
    else
    {
        $key = 1;

        $array[$key] = $value;
    }
    return $key;
}
?>

php_notes at ionws dot com (11-Oct-2005 12:17)

Note that key($array) returns NULL if $array's internal pointer goes past the end of the array.  For example, the following code:

<?php
$arr = array(
    'one' => '1',
    'two' => '2',
    'three' => '3',
    'four' => '4',
    'five' => '5');

for ($i = 0; $i < 10; $i++) {
    var_dump(key($arr));
    next($arr);
}
?>

results in:
string(3) "one"
string(3) "two"
string(5) "three"
string(4) "four"
string(4) "five"
NULL
NULL
NULL
NULL
NULL

Danniel@t h e - police (d'0't) com (22-May-2005 09:55)

To get the key name by position from Array:
<?php
$myArray['name1']=3;
$myArray['name2']=2;
$myArray['name3']=1;

echo($myArray[1]);   /* return NULL */
/* isset($myArray[1]) return false;   */
/* is_null($myArray[1]) return true;  */

function KeyName($myArray,$pos) {
   // $pos--;
   /* uncomment the above line if you */
   /* prefer position to start from 1 */

   if ( ($pos < 0) || ( $pos >= count($myArray) ) )
         return "NULL";  // set this any way you like

   reset($myArray);
   for($i = 0;$i < $pos; $i++) next($myArray);

   return key($myArray);
}

echo KeyName($myArray,1);  // result: name2
echo KeyName($myArray,2);  // result: name3
echo KeyName($myArray,3);  // result: "NULL"
?>

You can get any existing "key name" from array that is located at position $pos gived as second parameter. If no element is defined at given position the function will return the string "NULL".

Danniel@t h e - police (d'0't) com (22-May-2005 09:55)

To get the key name by position from Array:
<?php
$myArray['name1']=3;
$myArray['name2']=2;
$myArray['name3']=1;

echo($myArray[1]);   /* return NULL */
/* isset($myArray[1]) return false;   */
/* is_null($myArray[1]) return true;  */

function KeyName($myArray,$pos) {
   // $pos--;
   /* uncomment the above line if you */
   /* prefer position to start from 1 */

   if ( ($pos < 0) || ( $pos >= count($myArray) ) )
         return "NULL";  // set this any way you like

   reset($myArray);
   for($i = 0;$i < $pos; $i++) next($myArray);

   return key($myArray);
}

echo KeyName($myArray,1);  // result: name2
echo KeyName($myArray,2);  // result: name3
echo KeyName($myArray,3);  // result: "NULL"
?>

You can get any existing "key name" from array that is located at position $pos gived as second parameter. If no element is defined at given position the function will return the string "NULL".

happy dot machine at skynet dot be (06-May-2003 07:20)

<?php
$tab = array();
$tab[0] = 'php';
$tab[1] = '.';
$tab[2] = 'net';

// you will not enter the while
// $key = 0, while will consider $key as false
reset($tab);
while ($key = key($tab) ) {
echo $tab[$key];
next($tab);
}

// this will
reset($tab);
while (!is_null($key = key($tab) ) ) {
echo $tab[$key];
next($tab);
}

// when key() can't return a 'key', it return NULL
echo var_dump($key);
?>

kajetan at kajetan dot nu (04-Jul-2002 09:20)

I'm writing a forum and use an array to hold all the smiles. The keys in the array are the characters to write to get a smiley, and the data is the filename, like this
$Smiles[':-)'] = 'smile.gif'

To output all the smileys in a table with 3 columns, I wrote this code:

<?php
$the_end = false;

$s = reset($Smiles);
$k = key($Smiles);

while(!$the_end){
    echo '<tr>';
    for($i=0; $i<3; $i++){
        echo '<td>';
        if($the_end) echo '&nbsp;';
        else{
        echo $k.'< br><img src="'. $s .'">';
          $s = next($Smiles);
        if ($s==false) $the_end=true;
        else
            $k = key($Smiles);
        }
        echo "</td>\n";
    }
    echo "</tr>\n";
}
?>

I had to write a space in the < br> tag in the code above, because the board did a line brake otherwise.

mkeller at gmx dot de (11-Oct-2001 08:46)

In the case key() does not give you back the key(myarray) but "0", try this:
(Try this example without the line containing "end($myarray)" and you see my reason for this post...)

<?php
for($i = 0; $i <= 10; $i++) {
        $myarray[] = 'content '.$i;
        end($myarray);
        echo ('<br>key()='.key($myarray).' , content='.$myarray[$i]);
    }
?>

php at snr-graphics dot com (23-Mar-2001 07:50)

A Method of Multi-Dimensionalizing an Associative Array (This idea was designed with Graphics (image filenames in mind):

(A quick overview):
While working on a rather large web application, I found that I needed a way to obtain "all" the details on images used by the application, these images (by filename) were stored in the configuration file, in the form of associative arrays.

The following represents an example of how I tool those and converted them into multi-dimensional associative arrays.

<?php
do {
  $size = getImageSize($path.$myarray[key($myarray)]);
  if ($size[2] == '1') { $size[2] = 'gif'; }
  else if ($size[2] == '2') { $size[2] = 'jpg'; }
  else if ($size[2] == '3') { $size[2] = 'png'; }
  else if ($size[2] == '4') { $size[2] = 'swf'; }
  else { $size[2] = 'UNKNOWN'; }
$myarray[key($myarray)] = Array($myarray[Key($myarray)],$size[0],$size[1],$size[2],$size[3]);
} while (next($myarray));
?>

The end result is an multi-dim. associative array which contains the values:

<?php
$myarray["this"][0] = # filename.gif
$myarray["this"][1] = # width
$myarray["this"][2] = # height
$myarray["this"][3] = # type (converted to the file extension.)
$myarray["this"][4] = # height=x width=x
?>

This may not be all that impressive to some, but it turned out to be very useful for me, so I thought I'd share, in addition, I think it gives a "very" good example of "a use" for the Key() function.

Frankly, I was quite happy to discover this function, I can't count the number of times I "needed to use the key as a value".

I hope you find this code useful.