(PHP 4 >= 4.0.5, PHP 5)
array_search — Searches the array for a given value and returns the corresponding key if successful
   Searches haystack for needle.
  
needleThe searched value.
Note:
If
needleis a string, the comparison is done in a case-sensitive manner.
haystackThe array.
strict
       If the third parameter strict is set to TRUE
       then the array_search() function will search for
       identical elements in the
       haystack. This means it will also check the
       types of the
       needle in the haystack,
       and objects must be the same instance.
      
   Returns the key for needle if it is found in the
   array, FALSE otherwise.
  
   If needle is found in haystack
   more than once, the first matching key is returned. To return the keys for
   all matching values, use array_keys() with the optional
   search_value parameter instead.
  
This function may
return Boolean FALSE, but may also return a non-Boolean value which
evaluates to FALSE. Please read the section on Booleans for more
information. Use the ===
operator for testing the return value of this
function.
| Version | Description | 
|---|---|
| 5.3.0 | As with all internal PHP functions as of 5.3.0,
        array_search() returns NULLif invalid parameters
        are passed to it. | 
| 4.2.0 | Prior to PHP 4.2.0, array_search() returns NULLon failure instead ofFALSE. | 
Example #1 array_search() example
<?php
$array = array(0 => 'blue', 1 => 'red', 2 => 'green', 3 => 'red');
$key = array_search('green', $array); // $key = 2;
$key = array_search('red', $array);   // $key = 1;
?>