>PHP: constant

constant

(PHP 4 >= 4.0.4, PHP 5)

constant -- Devuelve el valor de una constante

DescripciÃ³n

mixed constant ( string nombre )

constant() devolverÃ¡ el valor de la constante indicada por nombre.

constant() es Ãºtil si necesita recuperar el valor de una constante, pero no conoce su nombre. Esto quiere decir, si estÃ¡ almacenada en una variable o es devuelta por una funciÃ³n.

Esta funciÃ³n trabaja tambiÃ©n con las constantes de clase.

Ejemplo 1. Ejemplo de constant()

<?php define("TAMMAX", 100); echo TAMMAX; echo constant("TAMMAX"); // igual que la linea anterior ?>

Vea tambiÃ©n define(), defined() y la secciÃ³n sobre Constantes.

add a note User Contributed Notes
constant

narada dot sage at googlemail dot com
13-Jul-2006 06:01


To access the value of a class constant use the following technique.



<?php



class a {

    const b = 'c';

}



echo constant('a::b');



// output: c



?>

service at dual-creators dot de
16-May-2006 10:00


It's easily to user constant() and define() to translate some words from your database-saves.



For example: 

You have a table userprofil and one coloumn is "gender".

Gender can be male or female but you will display "maennlich" or "weiblich" (german words for it - whatever...)



First step: Fetch into $Gender



Second:

define("male", "maennlich");

define("female", "weiblich");



Third:

echo constant($Gender);



Now, the index of the variable $Gender will be handled like a constant!



(It works like "echo male;" for better understanding)



And a result of this, it displays maennlich btw. weiblich!



greetz

Trevor Blackbird > yurab.com
18-Apr-2006 02:58


Technically you can define constants with names that are not valid for variables:



<?php



// $3some is not a valid variable name

// This will not work

$3some = 'invalid';



// This works

define('3some', 'valid');

echo constant('3some');



?>



Of course this is not a good practice, but PHP has got you covered.

timneill at hotmail dot com
26-Nov-2005 12:39


Please note when using this function from within a class to retrieve a php5 class constant, ensure you include the 'self::'.



class Validate

{

    const TEXT_MAX = 65536;

    

    //-- this will work

    public static function textWORKS($_value, $_type = 'TEXT')

    {

        $_max = constant('self::' . $_type . '_MAX');

        return (strlen($_value) <= $_max ? true : false);

    }

    

    //-- this will fail

    public static function textFAILS($_value, $_type = 'TEXT')

    {

        //-- Debug Warning: constant(): Couldn't find constant TEXT_MAX

        $_max = constant($_type . '_MAX');

        return (strlen($_value) <= $_max ? true : false);

    }

}

11-Oct-2005 07:20


In reply to VGR_experts_exchange at edainworks dot com



To check if a constant is boolean, use this instead:



<?php

if (TRACE === true)  {}

?>



Much quicker and cleaner than using defined() and constant() to check for a simple boolean.



IMO, using ($var === true) or ($var === false) instead of ($var) or (!$var) is the best way to check for booleans no matter what. Leaves no chance of ambiguity.

Joachim Kruyswijk
13-Nov-2004 09:12


The constant name can be an empty string.



Code:



define("", "foo");

echo constant("");



Output:



foo

VGR_experts_exchange at edainworks dot com
19-Sep-2003 05:32


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 01:10


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;


}


?>

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constant

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