PHP 4, PHP 5, PHP 7, PHP 8
defined - Checks whether a given named constant exists
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defined( string$constant_name ): bool

Checks whether the given constant exists and is defined.


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.



The constant name.

Return Values

Returns true if the named constant given by constant_name has been defined, false otherwise.

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