defined

Checks whether a constant with the given name exists

&reftitle.description; `bool` `defined` `string` `constant_name`

Checks whether a constant with the given `constant_name` is defined.

This function works also with class constants and enum cases.

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`.

&reftitle.parameters;

`constant_name`

- The constant name.

&reftitle.returnvalues;

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

&reftitle.examples;

### Checking Constants

    <?php

    /* Note the use of quotes, this is important. This example is checking
     * if the string 'TEST' is the name of a constant named TEST */
    if (defined('TEST')) {
        echo TEST;
    }

    interface bar {
        const test = 'foobar!';
    }

    class foo {
        const test = 'foobar!';
    }

    var_dump(defined('bar::test')); // bool(true)
    var_dump(defined('foo::test')); // bool(true)

    ?>

### Checking Enum Cases (as of PHP 8.1.0)

    <?php

    enum Suit
    {
        case Hearts;
        case Diamonds;
        case Clubs;
        case Spades;
    }

    var_dump(defined('Suit::Hearts')); // bool(true)

    ?>

&reftitle.seealso;

- `define`
- `constant`
- `get_defined_constants`
- `function_exists`
- The section on Constants