PHP/Data Structure/array keys

array_keys() function returns an array containing all keys

 
//If the search_element is included, then only the keys matching that particular element are returned; otherwise, all keys constituting the array are returned. 
//Its syntax is: array array_keys (array array, mixed [search_element])
//use array_keys() to return the key of a given element:
<?
$wines = array ("A" => "a","Q" => "q","E" => "e");
$labels = array_keys($wines);
print $labels;
print "<BR>";
$labels = array_keys($wines, "a");
print_r $labels;
?>

array_keys( ) returns an array of all the keys in that array

 
array array_keys ( array arr [, mixed search [, bool strict]] )
<?
    $users[923] = "T";
    $users[100] = "S";
    $users[1202] = "C";
    $userids = array_keys($users);

    $users[923] = "T";
    $users[100] = "S";
    $users[1202] = "C";
    $userids = array_keys($users, "T");
?>

Outputting Using array_values() and array_keys() for Backward Compatibility

 
<?
    $countries_languages = array("Germany" => "German", "France" => "French", "Spain" => "Spanish"); 
    
    printf("<p>Languages: %s.</p>\n", 
    implode(", ", array_values($countries_languages)) ); 
    
    printf("<p>Countries: %s.</p>\n", 
    implode(", ", array_keys($countries_languages)) ); 
    
?>

Return all the keys of an array with array array_keys (array input [, mixed search_value])

 
<?
$array = array(0 => 100, "color" => "red");
array_keys ($array); 
$array = array(1, 100, 2, 100);
array_keys ($array, 100); 
?>