CODEWITHSUNDEEP
phpconstants
ryanc1256
ryanc1256

Reputation: 1085

How to check if a defined constant exists?

I'm using a PHP framework called fuelphp, and I have this page that is an HTML file, so I can't use PHP in it. I have another file that has a top bar in it, which my HTML file will call through AJAX.

How do I check if a constant exists in PHP?
I want to check for the the fuelphp framework file locations.

These are the constants I need to check for (actually, I only have to check one of them):

define('DOCROOT', __DIR__.DIRECTORY_SEPARATOR);
define('APPPATH', realpath(__DIR__.'/fuel/app/').DIRECTORY_SEPARATOR);
define('PKGPATH', realpath(__DIR__.'/fuel/packages/').DIRECTORY_SEPARATOR);
define('COREPATH', realpath(__DIR__.'/fuel/core/').DIRECTORY_SEPARATOR);                    
require APPPATH.'bootstrap.php';

Upvotes: 92

Views: 128875

Answers (6)

Marlon
Marlon

Reputation: 1877

With defined you'll have to do something like that:

if (defined("CONST_NAME"))
    $value = CONST_NAME;

This will work, but you'll could get an annoying error message in your code editor (in my case Visual Studio Code with PHP Inteliphense extension) for the second line, since it wont find CONST_NAME. Another alternative would be to use the constant function. It takes an string as the constant name and returns null if the constant is not defined:

$value = constant("CONST_NAME");
if ($value != null)
{
    // Use the value ...
}

Since you passed the const name as a string, it wont generate an error on the code editor.

Upvotes: 1

Svetoslav Marinov
Svetoslav Marinov

Reputation: 1546

here's a cooler & more concise way to do it:

defined('CONSTANT') or define('CONSTANT', 'SomeDefaultValue');

credit: daniel at neville dot tk https://www.php.net/manual/en/function.defined.php#84439

Upvotes: 33

Niklas
Niklas

Reputation: 25391

Check using defined('CONSTANT') function.

An example from the manual:

<?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;
}
?>

Upvotes: 46

Tom Walters
Tom Walters

Reputation: 15616

Use defined() function, for example:

if (defined('VAR_NAME')) {
    // Something
}

Upvotes: 118

Eric MORAND
Eric MORAND

Reputation: 6786

First, these are not variables, but constants.

And you can check their existence by using the defined() function :

bool defined ( string $name )

Checks whether the given constant exists and is defined.

Upvotes: 107

Zac
Zac

Reputation: 1635

I take it you mean CONSTANTS not variables! the function is defined();

see here: defined

Upvotes: 5

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