PHP 4, PHP 5, PHP 7, PHP 8
define - Defines a named constant
Code Examples

define( string$constant_name, mixed$value, [bool$case_insensitive = false] ): bool

Defines a named constant at runtime.



The name of the constant.


It is possible to define constants with reserved or even invalid names, whose value can (only) be retrieved with constant. However, doing so is not recommended.


The value of the constant. In PHP 5, value must be a scalar value (int, float, string, bool, or null). In PHP 7, array values are also accepted.


While it is possible to define resource constants, it is not recommended and may cause unpredictable behavior.


If set to true, the constant will be defined case-insensitive. The default behavior is case-sensitive; i.e. CONSTANT and Constant represent different values.


Defining case-insensitive constants is deprecated as of PHP 7.3.0. As of PHP 8.0.0, only false is an acceptable value, passing true will produce a warning.


Case-insensitive constants are stored as lower-case.

Return Values

Returns true on success or false on failure.


Version Description
8.0.0 Passing true to case_insensitive now emits an E_WARNING. Passing false is still allowed.
7.3.0 case_insensitive has been deprecated and will be removed in version 8.0.0.
7.0.0 array values are allowed.

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