   #PHP Manual Miscellaneous functions define die

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                                    defined

   (PHP 3, PHP 4 )
   defined --  Checks whether a given named constant exists

Description

   bool defined ( string name)

   Returns TRUE if the named constant given by name has been defined,
   FALSE otherwise.

   Example 1. Checking Constants
   <?php
   /* Note the use of quotes, this is important.  This example is
   checking
   * if the string 'CONSTANT' is the name of a constant named CONSTANT */
   if (defined('CONSTANT')) {
       echo CONSTANT;
   }
   ?>

     Note: If you want to see if a variable exists, use isset() as
     defined() only applies to constants. If you want to see if a
     function exists, use function_exists().

   See also define(), constant(), get_defined_constants(),
   function_exists(), and the section on Constants.
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