What is the defined method in PHP?

The defined method can be used to check if a constant exists or not.

defined(string $constant_name): bool

This method returns true if the constant is defined, otherwise it returns false.

Example

<?php 
  define('ONE', 1);
  define('TWO', 2);
  echo "IS ONE DEFINED defined : ";
  var_dump(defined('ONE'));
  echo "\nIS TWO DEFINED defined : ";
  var_dump(defined('TWO'));
  echo "\nIS TEST defined : ";
  var_dump(defined('TEST'));
  echo "\nTesting Predefined Constants \n";
  echo("-------------------------");
  echo "\nIS PHP_VERSION defined : "; // predefined constant
  var_dump(defined('PHP_VERSION'));
?>

In the code above, we have created two constants, ONE and TWO. We used the defined method to check if the constants are available. For the constants ONE, TWO, and PHP_VERSION we will get true. For the TEST constant, we will get false since it is neither a predefined constant nor is it one defined by the program.

Free Resources

License: Creative Commons-Attribution-ShareAlike 4.0 (CC-BY-SA 4.0)