PHP: constant - Manual

Description

mixed constant ( string name )

constant() will return the value of the constant indicated by name.

constant() is useful if you need to retrieve the value of a constant, but do not know its name. i.e. It is stored in a variable or returned by a function.

Example 1. constant() example

<?php define("MAXSIZE", 100); echo MAXSIZE; echo constant("MAXSIZE"); // same thing as the previous line ?>

See also define(), defined() and the section on Constants.

User Contributed Notes
constant

thisisroot at gmail dot com
02-Feb-2005 09:34


FYI, this function works with class constants too.



Below is an example in which a database abstraction layer creates connections to different relational database systems based on class constants such as DBFission::CONNECTION_MYSQL, DBFission::CONNECTION_POSTGRESQL, etc. Using this function, I can convert text in an INI file to an integer constant easily.



<?php

// php voodoo to get a class constant based on a string

$type = constant( 'DBFission::CONNECTION_' . strtoupper( $c[ 'type']));



?>

Joachim Kruyswijk
13-Nov-2004 11:12


The constant name can be an empty string.



Code:



define("", "foo");

echo constant("");



Output:



foo

mina86 at tlen dot pl
04-Oct-2003 05:10


re PHPdotNET at 19-Oct-2002 08:02:

it is better tu use (no warning is generated so you don't have to use '@'):

<?php

if (!defined("<file-id>")) {

define("<file-id>", true);



// script content



}

?>

or

<?php

if (defined("<file-ide">)) return;



// script content

?>



You could also consider using include_once() and/or require_once();

VGR_experts_exchange at edainworks dot com
19-Sep-2003 07:32


Hello. This applies to constants being defined as Boolean values, and may-be applies generally.





I advise you to NOT use this in an included file, in a function or elsewhere outside the scope where the define('TRACE',TRUE) is placed) :





if (TRACE) {}





This will always evaluate to TRUE if the constant is not defined previously (the story about this becoming an string 'TRACE', thus evaluating to TRUE)





Use this :





<?php


if ((defined('TRACE'))AND(constant('TRACE')))  {}


?>

Andre
27-Apr-2003 03:10


Maybe this is useful:





$file_ext is the file Extension of the image





<?php


if ( imagetypes() & @constant('IMG_' . strtoupper($file_ext)) )


{


    $file_ext = $file_ext == 'jpg' ? 'jpeg' : $file_ext;


    $create_func = 'ImageCreateFrom' . $file_ext;


}


?>

23-Aug-2002 06:11


Think of this function as the constant version of "variable variables".

search for in the