How to determine whether PHP constant array key exists? -

i want use array constant in php 5.6. question is: how check whether key 'a' exists in array , "test2" return true well?

my code this:

const arr = array(    'a' => 'first',    'b' => 'second' );   $test1 = defined("arr"); $test2 = defined("arr['a']");  echo '<br>test1: '; var_dump($test1);  echo '<br>test2: '; var_dump($test2); 

result:

test1: bool(true) test2: bool(false)  

you need use array_key_exists function

var_dump(array_key_exists('a', arr)); 

defined() checks if constant defined , is, can additionaly check if constant array is_array(arr);

example:

<?php  const arr = array(    'a' => 'first',    'b' => 'second' );   $test1 = array_key_exists('a', arr); $test2 = array_key_exists('c', arr);  echo 'test1: '; var_dump($test1);  echo 'test2: '; var_dump($test2); 

output:

test1: bool(true) test2: bool(false) 

notice:

it work php version >= 5.6 working fiddle