defined

Definition and usage

defined() function checks whether the constant exists.

Return true if the constant exists, otherwise return false.

Example

Check if the constant exists:

 <?php
define ( "GREETING" , "Hello world!" ) ;
echo defined ( "GREETING" ) ;
?>

Try it yourself

Example explanation:

In the above example, the define() function is used to create a constant named GREETING, and defined() function checks whether the constant exists. If present, the echo statement outputs 1 (in PHP, TRUE is considered 1 when used for output), indicating that the constant is indeed defined. If the constant is not defined, the output will be empty or 0 (for FALSE).

grammar

 defined ( name )