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PHP define() Function

❮ PHP Misc Reference


Define a case-sensitive constant:

define("GREETING","Hello you! How are you today?");
echo constant("GREETING");
Try it Yourself »

Definition and Usage

The define() function defines a constant.

Constants are much like variables, except for the following differences:

  • A constant's value cannot be changed after it is set
  • Constant names do not need a leading dollar sign ($)
  • Constants can be accessed regardless of scope
  • Constant values can only be strings and numbers



Parameter Values

Parameter Description
name Required. Specifies the name of the constant
value Required. Specifies the value of the constant.
case_insensitive Optional. Specifies whether the constant name should be case-insensitive. Possible values:
  • TRUE - Case-insensitive (deprecated in PHP 7.3)
  • FALSE - Case-sensitive (this is default)

Technical Details

Return Value: Returns TRUE on success or FALSE on failure
PHP Version: 4+
Changelog: PHP 7.3: Defining case-insensitive constants is deprecated.
PHP 7: The value parameter can also be an array.
PHP 5: The value parameter must be a string, integer, float, boolean or NULL.

❮ PHP Misc Reference