array_key_exists()

(PHP 4 >= 4.0.7, PHP 5, PHP 7)

检查数组里是否有指定的键名或索引

说明

array_key_exists(mixed $key,array $array): bool

数组里有键$key时，array_key_exists()返回TRUE。$key可以是任何能作为数组索引的值。

参数

$key

要检查的键。

$array

一个数组，包含待检查的键。

返回值

成功时返回TRUE，或者在失败时返回FALSE。

Note:

array_key_exists()仅仅搜索第一维的键。多维数组里嵌套的键不会被搜索到。

范例

Example #1array_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";
}
?>

Example #2array_key_exists()与isset()的对比

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);
?>

注释

Note:

由于为了兼容以前版本，如果object当做$array传入array_key_exists()，同时$key是对象的属性，也会返回TRUE。不要依赖这个特性，保证参数$array类型是数组（array）。

要检查对象是否有某个属性，应该去用property_exists()。

参见

• isset() 检测变量是否已设置并且非 NULL
• array_keys() 返回数组中部分的或所有的键名
• in_array() 检查数组中是否存在某个值
• property_exists() 检查对象或类是否具有该属性

If you want to take the performance advantage of isset() while keeping the NULL element correctly detected, use this:
if (isset(..) || array_key_exists(...))
{
...
}
Benchmark (100000 runs):
array_key_exists() : 205 ms
is_set() : 35ms
isset() || array_key_exists() : 48ms
Note: 
The code for this check is very fast, so you shouldn't warp the code into a single function like below, because the overhead of calling a function dominates the overall performance.
function array_check(...)
{
  return (isset(..) || array_key_exists(...))
}

You'll notice several notes on this page stating that isset() is significantly faster than array_key_exists(). This may be true except for one small hitch. isset() will return false for arrays keys that have there value set to NULL, which is therefore not entirely accurate.
Example:
<?php
$foo = array();
$foo['bar'] = NULL;
var_dump(isset($foo['bar']));
var_dump(array_key_exists('bar', $foo));
?>
will output:
bool(false)
bool(true)
Be aware of this!

Beware that if the array passed to array_key_exists is NULL, the return value will also be NULL. 
This is undocumented behaviour, moreover the documentation (and return typehint) suggest that the array_key_exists function only returns boolean value. But that's not the case.

This function will return NULL when second argument is not an array. So it will bite you when using it like that:
<?php
$not_an_array = null;
if (array_key_exists($key, $not_an_array) === false) {
  // the array doesn't have the key
  return;
}
// happily proceed - surely the array does have the key (BUT IT DOESN'T!)
?>
That's because the condition null === false fails.
Instead you should use:
<?php
if (array_key_exists($key, $not_an_array) == false) {
  return;
}
// or
if (!array_key_exists($key, $not_an_array)) {
  return;
}
// or
if (is_array($not_an_array) === false || array_key_exists($key, $not_an_array) === false) {
  return;
}
?>

Rudi's multidimensional array_key_exists function was not working for me, so i built one that is.
Enjoy.
function array_multi_key_exists( $arrNeedles, $arrHaystack){
  $Needle = array_shift($arrNeedles);
  if(count($arrNeedles) == 0){
    return(array_key_exists($Needle, $arrHaystack));
  }else{
    if(!array_key_exists($Needle, $arrHaystack)){
      return false;
    }else{
      return array_multi_key_exists($arrNeedles, $arrHaystack[$Needle]);
    }
  }
}

The way array_key_exists handles null, float, boolean, and 'integer-representing string' keys is inconsistent in itself and, in the case of bool and float, with the way these are converted when used as array offset.
<?php
$array = array(null => 1, false => 2, true => 3, 4.6 => 4, "08" => 5, "8" => 6);
var_export($array);
echo "\nnull is " . (array_key_exists(null, $array) ? '' : 'not ') . "a key.\n";
echo 'false is ' . (array_key_exists(false, $array) ? '' : 'not ') . "a key.\n";
echo 'true is ' . (array_key_exists(true, $array) ? '' : 'not ') . "a key.\n";
echo '4.6 is ' . (array_key_exists(4.6, $array) ? '' : 'not ') . "a key.\n";
echo '"08" is ' . (array_key_exists("08", $array) ? '' : 'not ') . "a key.\n";
echo '"8" is ' . (array_key_exists("8", $array) ? '' : 'not ') . "a key.\n";
?>
Output:
array (
 '' => 1,
 0 => 2,
 1 => 3,
 4 => 4,
 '08' => 5,
 8 => 6,
)
null is a key.
false is not a key.
true is not a key.
4.6 is not a key.
"08" is a key.
"8" is a key.
Well, and you get this warning three times (on the bools and the float, but not on the null):
Warning: array_key_exists() [function.array-key-exists]: The first argument should be either a string or an integer in /var/www/php/test.php on line 6

Very simple case-insensitive array_key_exists:
bool (in_array(strtolower($needle), array_map('strtolower', array_keys($haystack))))

I've got a new take on the multi key function I would like to share.
<?php 
function array_multi_key_exists(array $arrNeedles, array $arrHaystack, $blnMatchAll=true){
  $blnFound = array_key_exists(array_shift($arrNeedles), $arrHaystack);
  
  if($blnFound && (count($arrNeedles) == 0 || !$blnMatchAll))
    return true;
  
  if(!$blnFound && count($arrNeedles) == 0 || $blnMatchAll)
    return false;
  
  return array_multi_key_exists($arrNeedles, $arrHaystack, $blnMatchAll);
}
?>
Hope you'll find it usefull.

array_key_exists perfect for $_GET .
As there will be browser level restriction on length of URL , number of keys in $_GET global variable will be very limited . So array_key_exists will not cause any performance overhead in this context . isset function can be conveniently ignored while handling $_GET variable.
But for $_POST , the max array size has to be configure in server PHP configuration . So cannot rely on array_key_exists for $_POST if max array size is not optimized . 
Here is an example with array_key_exists switching between content-types :
if(array_key_exists('format',$_GET))
{
       if($_GET['format']=="json")
       { 
           header('Content-Type: application/json');
       }
       else{
           //handle any other format whitelisted for the application
       }
}
else {
        error_log("format parameter missing . using default html format");
        header('Content-Type: text/html');
}

The argument of array_key_exists() vs. isset() came up in the workplace today, so I conducted a little benchmark to see which is faster:
<?php
  // one-dimensional arrays
  $array = array_fill(0,50000,'tommy is the best!');
  $arraykeyexists_result = array();
  $start = microtime(true);
  for ($i = 0; $i < 100000; $i++) {
    if (array_key_exists($i,$array)) {
      $arraykeyexists_result[] = 1;
    }
    else {
      $arraykeyexists_result[] = 0;
    }
  }
  $arrtime = round(microtime(true)-$start,3);
  
  $start = microtime(true);
  for ($i = 0; $i < 100000; $i++) {
    if (isset($array[$i])) {
      $arraykeyexists_result[] = 1;
    }
    else {
      $arraykeyexists_result[] = 0;
    }
  }
  $istime = round(microtime(true)-$start,3);
  
  $totaltime = $arrtime+$istime;
  $arrpercentage = round(100*$arrtime/$totaltime,3);
  $ispercentage = round(100*$istime/$totaltime,3);  
  
  echo "array_key_exists(): $arrtime [$arrpercentage%] seconds\n";
  echo "isset():      $istime [$ispercentage%] seconds\n";
?>
On Windows, the output is similar to
array_key_exists(): 0.504 [82.895%] seconds
isset():      0.104 [17.105%] seconds
On Mac or Linux, isset() is faster but only by a factor of approximately 1.5.

I took hours for me to debug, and I finally recognized that,
You have to reset the $array before using array_key_exists 
reset($array);
array_key_exists($needle,$array);
Or you will get no reply.

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.";
}
?>

As you might know, isset() is actually working like @$variable===NULL. As the result, it doesn't actually catch variables set to NULL. If you want to check if variable is set (even to NULL), you can use array_key_exists on $GLOBALS, like there.
<?php
  $me = null;
  $se = 1;
  unset($se);
// $he is not set
if(array_key_exists('me', $GLOBALS)) echo "\$me exists\n";
if(array_key_exists('se', $GLOBALS)) echo "\$se exists\n";
if(array_key_exists('he', $GLOBALS)) echo "\$he exists\n";
?>
In this case, only $me will be detected as $se was removed when code was running and $he was never set.

Here is a little function for case sensitivity to elaborate on what was said by MarkL from ##php (Freenode) and mmanning at mdanderson dot org from this page:
<?php
// Case sensitive version of array_key_exists() using preg_match()
function array_ikey_exists($key,$arr)
{
  if(preg_match("/".$key."/i", join(",", array_keys($arr))))        
    return true;
  else
    return false;
}
?>
Not that anyone else couldn't have written this, but a concept like this strengthens reusability. :)
Also, I've been running into issues with escaping for Regex, so I decided to give something like this a shot:
<?php
function array_ikey_exists($key,$arr)
{
  $e = 0; //$key = addslashes($key);
  if(is_array($arr) && $arr !==array())
  {
    foreach($arr as $k => $v)
    {  
      if(strtolower($k) == strtolower($key))
        $e++;
    }
    if($e>0)
      return true;    
    else
      return false;
  }
  else
    return false;
}
?>
You could addslashes() to escape; it's just another approach.

A little function which take an array as keys
<?php
//note the s in the function name (keys)
function array_keys_exists($array,$keys) {
  foreach($keys as $k) {
    if(!isset($array[$k])) {
    return false;
    }
  }
  return true;
}
?>
//useful to validate a form for example
<form>
  <input type="text" name="field1" /><br />
  <input type="text" name="field2" /><br />
  <input type="text" name="field3" /><br />
  <input type="text" name="field4" /><br />
  <input type="text" name="field5" /><br />
</form>
<?php
if(!array_keys_exists($_POST,
array("field1","field2","field3","field4","field5")
)) {
  //some fields are missing, dont do anything (maybe hacking)
} else {
  //code ...
}
?>

array_key_exists doesn't work with objects implementing ArrayAccess interface. It also ignores possible __get() method in such objects, despite the fact it accepts object as a second parameter. It works only with 'real' properties.
<?php
class A implements ArrayAccess {
  public $data;
  public function offsetExists($offset) {
    return isset($this->data[$offset]);
  }
  public function __get($property) {
    return $this->data[$property];
  }
}
$a = new A();
$a->data['somekey'] = 1;
var_dump(array_key_exists('somekey', $a)); // returns false
var_dump(array_key_exists('data', $a)); // returns true
?>

I just want to note that array_key_exists() can be extremely slow for large (>200 keys) arrays. Use isset($array($key)) instead! My program ran in 3 minutes instead of 2 hours after switching to isset()!

array_key_exists(), at least in 5.2.4, passes the array by value. I conclude this from seeing performance worsen as the array to search got bigger. isset() doesn't have this problem.

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

Here's a function to return a reference to the first array element that has a given key. The code works for multidimensional arrays:
<?php
function &array_find_element_by_key($key, &$form) {
 if (array_key_exists($key, $form)) {
  $ret =& $form[$key];
  return $ret;
 }
 foreach ($form as $k => $v) {
  if (is_array($v)) {
   $ret =& array_find_element_by_key($key, $form[$k]);
   if ($ret) {
    return $ret;
   }
  }
 }
 return FALSE;
}
?>

this function very good to use if you need to verify many variables:
<?php
function array_key_exists_r($keys, $search_r) {
  $keys_r = split('\|',$keys);
  foreach($keys_r as $key)
  if(!array_key_exists($key,$search_r))
  return false;
  return true;
}
?>
e.g.
<?php
if(array_key_exists_r('login|user|passwd',$_GET)) {
// login
} else {
// other
}
?>
works for me, enjoy.
dg shaw.

I saw some examples above for array_keys_exist() or functions to see if multiple keys exist in a given array and return false if any of them don't.
Here is a simpler way to do this:
<?php
function array_keys_exist($keys,$array) {
  if (count (array_intersect($keys,array_keys($array))) == count($keys)) {
    return true;
  }
}
$array = array ('filename' => 'myfile', 'filesize' => 1234, 'filepath' => '/tmp/myfile');
$keys = array('filename','filesize','filepath');
echo array_keys_exist($keys,$array);
//returns true
$keys[] = "somethingelse";
echo array_keys_exist($keys,$array);
//Returns false
?>

Be warned that before checking the key existence with isset() it will be typecasted to integer if it is not a string or integer! 
See in http://php.net/manual/en/language.types.array.php
I.e. 
$a = ['test']; // 'test' will have key 0
$key = false;
var_dump(isset($a[$key]) ); // true

if you ever face a case in which your array_key_exists returns null, that might be because the second parameter you gave it is not an array.
For instance :
  var_dump(array_key_exists($my_key,$my_array));
  //bool(true);
  var_dump(array_key_exists($my_array, $my_key));
  //NULL

Hey, this function is able to rename a key inside an array.
If the key to be replaced doesn't exist inside the array, or the new key already exists in the array, the function will return FALSE.
Otherwise, the array with the renamed key will be returned.
Hope this will be useful for someone.
<?php
function array_rename_key($array, $key, $newkey){
  if( ! array_key_exists($key, $array) || array_key_exists($newkey, $array)) return FALSE;
  $uid = uniqid(''); //To clearly identify the Element.
  $preserve_value = $array[$key]; //Keep the Value
  $array[$key] = $uid; //Overwrite Value with ID
  $array = array_flip($array); //Flip the Array keys and values
  $array[$uid] = $newkey; //Set Value of the ID with new Key.
  $array = array_flip($array); //Everything back in Place.
  $array[$newkey] = $preserve_value;
  return $array;
}
?>

I created this function that uses array key exist to compare a form and a table to see if something has changed.
This can be very helpfull if you need to update a table record from a form but you do not want to display all table fields.
<?php
function($data_from_db, $form_data) {
 $data = $data_from_db;
 $keys = array_keys($data);
  for($i = 0; $i < count($data); $i++) {
    if(!array_key_exists($keys[$i], $form_data)) {
      $dbobject->$keys[$i] = $data[$keys[$i]];
    } else {
      $dbobject->$keys[$i] = $form_data[$keys[$i]];
    }
  }
  return $dbobject;
}
?>
you can then use the dbobject to update the table.

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.

<?php
/*
  It also works on objects
  ***************************************
*/
class PHP
{
  private $compiler;
  protected $architecture;
  public $version;
  public $system = "Linux";
  
}
$php = new PHP();
$a = array_key_exists('compiler', $php);   # false
$b = array_key_exists('architecture', $php); # false
$c = array_key_exists('version', $php);   # true
$d = array_key_exists('system', $php);    # true
var_dump( $a, $b, $c, $d );
?>

While working with large JSON datastructures I encountered an increasing need to check the presence of certain data all over the place.
This led to the function below that lets you simply access the data, and returns it if available, null if not.
Note that it uses a variable number of parameters, you can go as deep into a nested structure as you want.
<?php
function safe_array_access($ar){
  $numargs = func_num_args();
  $arg_list = func_get_args();
  $aritterator = $ar;
  for($i = 1; $i < $numargs; $i++){
    if (isset($aritterator[$arg_list[$i]]) || array_key_exists($arg_list[$i], $aritterator)){
      $aritterator = $aritterator[$arg_list[$i]];
    }else{
      return(false);
    }
  }
  return($aritterator);
}
?>
Usage:
Instead of $a['b']['c'] use safe_array_access($a, 'b', 'c');

This uses array_key_exists.
You have a multidimensional array of the form:
$rowsoriginal[] = array('field_wrkvolmin_value' => 216, 'field_wrkvolmax_value' => 1000);
$rowsoriginal[] = array('field_wrkvolmin_value' => 27, 'field_wrkvolmax_value' => 216);
Using print_r this will look like:
Array ( [0] => Array ( [field_wrkvolmin_value] => 216 [field_wrkvolmax_value] => 1000 ) [1] => Array ( [field_wrkvolmin_value] => 27 [field_wrkvolmax_value] => 216 ) )
This can be used to create a table by iterating over the rows that looks like this:
field_wrkvolmin_value     field_wrkvolmax_value
      216                   1000
      27                    216
when $rowsoriginal contain a fixed but unknown amount of values.
If you want to process this in an automatic way without knowing the keys etc, into a multidimensional array of the form:
$rowstemp = array('field_wrkvolmin_value' => array(216, 27), 'field_wrkvolmax_value' => array(1000, 216));
Using print_r this will look like:
Array ( [field_wrkvolmin_value] => Array ( [0] => 216 [1] => 27 ) [field_wrkvolmax_value] => Array ( [0] => 1000 [1] => 216 ) )
This can be used to iterate over the rows of a table to create a table in the form of:
field_wrkvolmin_value      216      27
field_wrkvolmax_value      1000      216
To do this you can use the following looping and conditional structure, using array_key_exists():
<?php
$rowstemp = array();
foreach ($rowsoriginal as $row) {
  foreach ($row as $key => $value) {
    if (array_key_exists($key, $rowstemp)) {
      $rowstemp[$key][] = $value;
    }
    else {
      $valuestemp = array($value);
      $rowstemp[$key] = $valuestemp;
    }
  }
}
?>

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'.

An even simpler case-insensitive alternative to array_key_exists():
<?php
array_key_exists(strtolower($key), array_change_key_case($search));

If u want to check if a key exists either in the array or in any subarray try the following:
<?php
function requireKey($needle, array $array)
  {
    foreach ($array as $key => $value) {
      if ($key === $needle) return $value;
      if (is_array($value)) {
        if ($x = $this->requireKey($key, $value)) return $x;
      }
    }
    return false;
  }
?>
(( return $value for recursive array search, return true for recursive array key exists ))

The multi_array_key_exists() function posted by alishahnovin at hotmail dot com [which has since been removed] does not always return the expected result.
This modified version does.
<?php
/**
 * multi_array_key_exists function.
 * 
 * @param mixed $needle The key you want to check for
 * @param mixed $haystack The array you want to search 
 * @return bool
 */
function multi_array_key_exists( $needle, $haystack ) {
 
  foreach ( $haystack as $key => $value ) :
    if ( $needle == $key )
      return true;
    
    if ( is_array( $value ) ) :
       if ( multi_array_key_exists( $needle, $value ) == true )
        return true;
       else
         continue;
    endif;
    
  endforeach;
  
  return false;
}
?>

This function will look for a key in multidimensional arrays, and return the paths to all the results found, or return false if none have been found.
<?php
function array_multi_key_exists($key, $array, $first=true, &$return=array()){
if($first){
while($ret = array_multi_key_exists($key, &$array, false)){
$r[]=$ret;
}
if(empty($r[0])){
return $r[0]=array();
}else{
return $r;
}
}
foreach($array as $k => $v){
if($k === $key && !(is_array($v))){
unset($array[$k]);
array_unshift($return, $k);
return $return;
}elseif($k === $key && is_array($v)){
if(empty($v)){
unset($array[$k]);
}else{
if(array_multi_key_exists($key, &$array[$k], false, $return)){
array_unshift($return, $k);
return $return;
}
}
array_unshift($return, $k);
unset($array[$k]);
return $return;
}else{
if(is_array($v)){
if(array_multi_key_exists($key, &$array[$k], false, $return)){
array_unshift($return, $k);
return $return;
}
}
}
}
return false;
}
?>
The next function takes the array of paths returned by array_multi_key_exists as parameter and returns the corresponding values.
<?php
function array_multi_values($paths, $array){
$return = array();
foreach($paths as $n => $path){
$val = $array;
foreach($path as $dim => $key){
$val = $val[$key];
}
$return[$n] = $val;
unset($val);
}
return $return;
}
?>
This next function takes the paths array returned by array_multi_key_exists, and unsets the corresponding values of the original array, returning the clipped array.
<?php
function array_multi_clip($paths, $array, $key=0, $path=false){
while($path==false){
foreach($paths as $path){
array_multi_clip($paths, &$array, 0, $path);
}
return $array;
}
$n = count($path);
if($key == $n-1){
unset($array[$path[$key]]);
return $array;
}else{
array_multi_clip($paths, &$array[$path[$key]], ++$key, $path);
}
}
?>
Examples:
<?php
$array = array(
'colours' => array(
'red' => array(
'veg' => 'tomato',
'fruit' => 'strawberry',
'green' => 'colourblind',
),
'green' => array(
'green' => 'envy',
'unripe' => 'veggies',
),
'blue' => 'smurfs',
),
);
$key = 'green';
$paths = array_multi_key_exists($key, $array);
print_r($paths);
?>
The result will be an array of paths:
Array
(
  [0] => Array
    (
      [0] => colours
      [1] => red
      [2] => green
    )
  [1] => Array
    (
      [0] => colours
      [1] => green
      [2] => green
    )
  [2] => Array
    (
      [0] => colours
      [1] => green
    )
)
As it can be seen, if one of the results is an array which again contains the key searched, both will show up in the results.
Example of array_multi_values:
<?php
$values = array_multi_values($paths, $array);
print_r($values);
?>
Result:
<?php
Array
(
  [0] => colourblind
  [1] => envy
  [2] => Array
    (
      [green] => envy
      [unripe] => veggies
    )
)
?>
Example of array_multi_clip():
<?php
$clipped = array_multi_clip($paths, $array);
print_r($clipped);
?>
Result:
<?php
Array
(
  [colours] => Array
    (
      [red] => Array
        (
          [veg] => tomato
          [fruit] => strawberry
        )
      [blue] => smurfs
    )
)
?>