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array_key_exists

(PHP 4 >= 4.1.0, PHP 5)

array_key_exists -- 检查给定的键名或索引是否存在于数组中

说明

bool array_key_exists ( mixed key, array search )

array_key_exists() 在给定的 key 存在于数组中时返回 TRUE。key 可以是任何能作为数组索引的值。array_key_exists() 也可用于对象。

例 1. array_key_exists() 例子

<?php
$search_array = array('first' => 1, 'second' => 4);
if (array_key_exists('first', $search_array)) {
    echo "The 'first' element is in the array";
}
?>

注意: 在 PHP 4.0.6 中本函数名为 key_exists()。

例 2. array_key_exists() 与 isset() 对比

isset() 对于数组中为 NULL 的值不会返回 TRUE，而 array_key_exists() 会。

<?php
$search_array = array('first' => null, 'second' => 4);

// returns false
isset($search_array['first']);

// returns true
array_key_exists('first', $search_array);
?>

参见 isset()，array_keys() 和 in_array()。


add a note add a note User Contributed Notes
sj-b at hotmail dot de
01-Aug-2007 04:14
i dont like how empty() works.
an integer with value 0 or a boolean wth
value false (same like zero) counts as
empty too.

[code]function r_empty (&$check)
{
   if (!isset($check)) return true;
   if ($check == NULL) return true;
   return false;
}[/code]

that is a good replacement for
both functions for me.
Lucknut dot xbl at googlemail dot com
18-Jul-2007 05:44
I found this function very good to use if your want your urls like index.php?login or index.php?register
e.g.
<?php
if( array_key_exists( 'home',$_GET ) ) {
   echo "Home - its where the heart is.";
} else if( array_key_exists( 'login',$_GET ) ) {
   echo "Login code here!";
} else if( array_key_exists( 'register',$_GET ) ) {
   echo "Register code here!";
} else {
   echo "Home - its where the heart is.";
}
?>
david at madole dot net
06-Jul-2007 03:11
Regarding performance differences between isset() and array_key_exists(), the differences may be there, but the function are not always interchangable.

Note that when $a[1] = null then isset($a[1]) == false but array_key_exists(1, $a) == true
eidberger at jakota dot de
11-Jun-2007 08:14
Just wondered why array_key_exists() makes me a cpu-load of 85% while isset() only needs 35%.

Not a big thing for one time execution, but in my case it have to check 1-dimensional array with ~ 15.000 entries 100 times a second. My code checks a big array for existing entrys and updates them, if needed.

Hopes it helps somebody. Notice that on many other functions, which makes coding more comfortable at the cost of speed.
alishahnovin at hotmail dot com
28-May-2007 05:47
Seems the array_key_exists can't find a key in a multidimensional array...

Here's my fix...

<?php

function multi_array_key_exists($needle, $haystack) {
  foreach ($haystack as $key=>$value) {
   if ($needle==$key) {
     return true;
   }
   if (is_array($value)) {
     multi_array_key_exists($needle, $value);
   }
  }
  return false;
}

?>
php at ianco dot co dot uk
09-Apr-2007 08:58
array_key_exists is case sensitive (at least in PHP 4.3.9). To make a case-insensitive comparison you could use strtolower on both sides.
inker2576 at yahoo dot com
07-Mar-2007 04:01
Further research on this has turned up that the performance problems are a known, confirmed bug in PHP 5.1.x, and have been fixed in PHP builds after September 2006.  You can find the bug report here:  http://bugs.php.net/bug.php?id=38812

However, just because it's a fixed bug doesn't really change the conclusion.  If you're writing a script and there's any chance it could be used on a PHP 5.1.x server, you should still avoid this function and use isset() or some other kind of test if you want it to run efficiently.
serkan yersen
07-Feb-2007 12:01
marzetti.marco,
I fixed your function it's is more optimized and working better now.

function regex_array_keys($arr, $pattern){
   $results[] = false;

   if(!is_array($arr))
       return false;

   foreach($arr as $key => $val){
         if(!is_array($key))
       if(preg_match($pattern,$key))
             array_push($results,$key);
   }

   return $results;
}
brauliorossi at gmail dot com
25-Jan-2007 05:42
Matt and mikael dot knutsson at gmail dot com:

this outputs bool(true):

$ar = array ( 'outter' => array ( 'inner' => 1 ) );
var_dump(array_key_exists('inner', $ar['outter']));
mikael dot knutsson at gmail dot com
16-Dec-2006 06:50
You're right, I'm not sure what I did wrong since I had a problem where array_key_exists returned true, while
<?php
$keys = array_keys( $array );
var_dump( in_array( 'key', $keys ) );
?>
returned false. (Which does the exact same thing) I probably either messed up the array, or the order in one of the array calls.
I rewrote the entire section where I had this problem (which was probably a good idea anyway), so I don't have any demonstration code.
Matt
01-Dec-2006 09:50
mikael dot knutsson at gmail dot com:
I don't think it does, at least in PHP5?

For example, this outputs bool(false):

$ar = array ( 'outter' => array ( 'inner' => 1 ) );
var_dump(array_key_exists('inner', $ar));

So it doesn't actually check the inner array for the key 'inner'.
mikael dot knutsson at gmail dot com
25-Nov-2006 12:05
When dealing with multi-dimensional arrays, this function checks through all keys in the array, including the "child arrays" unlike the array_keys( array, $search ) function which would only check and return from the first level of keys.

Took me a couple of minutes to figure out what was wrong and I hope it helps some people when looking for the right function.
Mike Toppa
03-Aug-2006 05:43
At least in PHP 4.4.0, array_key_exists is inconsistently sensitive to different data types. For example, if your first argument is a double and the keys in your array are integers, array_key_exists will always return false. If you then cast the first argument to an integer, or even to a string, then you can successfully match. I haven't tested all the possibilities, to see when it'll tolerate different data types and when it won't, so the easiest and safest solution is to cast your first argument to match the data type of the keys.
ncurtis at cenicola-helvin dot com
09-Jul-2006 10:25
array_key_exists() does not check values in the key i wrote this function to check if a key in an array has a empty value as corresponds to values that return true for empty() an redirects to a page if specified otherwise returns false

<?php
function keysExists($array, $startingIndex, $redirectPage) {
   if(is_array($array)) {
       if (!empty($startingIndex)) {
           for ($i = 0; $i < $startingIndex; $i++) {
               next($array);
           }
       }
       while(list($key, $value) = each($array)) {
           if (empty($value)) {
               if (!empty($redirectPage)) {
                   header("Location: $redirectPage");
               } else {
                   return FALSE;
               }
           }
       }
   } else {
       return FALSE;
   }
}
?>
email me and let me no if you found this useful!
marzetti.marco at gmail.com
06-Jul-2006 09:44
Returns the keys in $arr matching $pattern in a regex

<?php

function regex_array_keys ( &$arr, $pattern ) {
   $results[] = false;
   if( !is_array( $arr ) )
       return false;
  
   while( !is_null( $key = key( $arr ) ) ) {
      
       if( preg_match( $pattern, $key ) )
           $results[] = $key;
       next($arr);
   }
   reset( $arr );
  

   return $results;
}

?>
09-May-2006 03:44
property_exists() does the same thing for object properties.
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