array_keys() Definition and Usage
array_keys() function returns a new array containing all the key names in the array.

If the second parameter is provided, only the key name with the key value of this value will be returned.

If the strict parameter is specified as true, PHP will use equality comparison (===) to strictly check the data type of the key value.

Syntax
array_keys(array,value)
Parameter Description
array required. Specifies the input array.
value Optional. The index (key) of the specified value.
strict Optional. Used with the value parameter. Possible values:

true - Returns the key with the specified value based on the type.
false - Default value. Does not depend on type.


Example 1

<?php 
$a=array("a"=>"Horse","b"=>"Cat","c"=>"Dog"); 
print_r(array_keys($a)); 
?>

Output:

Array ([0] => a [1] => b [2] => c )
Example 2
Use value parameter:

<?php 
$a=array("a"=>"Horse","b"=>"Cat","c"=>"Dog"); 
print_r(array_keys($a,"Dog")); 
?>

Output:

Array ([0] => c)
Example 3
Use strict parameter (false ):

<?php 
$a=array(10,20,30,"10"); 
print_r(array_keys($a,"10",false)); 
?>

Output:

Array ( [0] => 0 [1] => 3 )
Example 4
Use strict parameter (true):

<?php 
$a=array(10,20,30,"10"); 
print_r(array_keys($a,"10",true)); 
?>

Output:

Array ([0] => 3)

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