如何在 PHP 中定义常量

Question

I do not understand how this code work. displaying code below , in this code i defined a constant and the value is 10 but it display the output "constant is not defined".

why?

define('HELLO', 10);        
if(defined(HELLO))        
{        
    echo "Constant is defined";        
}        
else        
{        
    echo "Constant is not defined";        
}        

?>

Answer 1

change:

defined(HELLO)

to:

defined('HELLO')

http://php.net/manual/en/function.defined.php

Answer 2

Define Constant in PHP:

define("HELLO", 10);

If condition needs to change, then: defined("HELLO")

Answer 3

Even you can follow this way of checking and defining constant in PHP.

defined('CONSTANT') or define('CONSTANT', 'SomeDefaultValue');

For your question, you have made a mistake of quote . follow as :

if(defined('HELLO')){
  echo "Constant is already defined";
}else{
  echo "Constant is not defined, you can define it.";
}

https://www.php.net/manual/en/function.defined.php#84439