define> <connection_timeout
Last updated: Fri, 16 Jul 2010

constant

(PHP 4 >= 4.0.4, PHP 5)

constant — Retorna o valor de uma constante

Descrição

mixed constant ( string $name )

Retorna o valor de uma constante indicada pelo parâmetro name.

A função constant() é útil se você precisa pegar o valor de uma constante, mas não sabe o seu nome. I.e. esta guardada em uma variável ou é retornada por uma função.

Esta função funciona também com constantes de classes.

Parâmetros

name

O nome da constante.

Valor Retornado

Retorna o valor da constante, ou NULL se o constante não é definida.

Exemplos

Exemplo #1 Exemplo da constant()

<?php
define("MAXSIZE", 100);
echo MAXSIZE;
echo constant("MAXSIZE"); // mesma coisa que a linha anterior


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

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

$const = 'test';

var_dump(constant('bar::'. $const)); // string(7) "foobar!"
var_dump(constant('foo::'. $const)); // string(7) "foobar!"

?>

Veja Também



define> <connection_timeout
Last updated: Fri, 16 Jul 2010
 
User Contributed Notes
constant
bohwaz
05-Jul-2010 10:28
Return constants from an object. You can filter by regexp or match by value to find a constant name from the value.

Pretty useful sometimes.

<?php

function findConstantsFromObject($object, $filter = null, $find_value = null)
{
    $reflect = new ReflectionClass($object);
    $constants = $reflect->getConstants();
   
    foreach ($constants as $name => $value)
    {
        if (!is_null($filter) && !preg_match($filter, $name))
        {
            unset($constants[$name]);
            continue;
        }
       
        if (!is_null($find_value) && $value != $find_value)
        {
            unset($constants[$name]);
            continue;
        }
    }
   
    return $constants;
}

?>

Examples :

<?php

class Example
{
    const GENDER_UNKNOW = 0;
    const GENDER_FEMALE = 1;
    const GENDER_MALE = 2;

    const USER_OFFLINE = false;
    const USER_ONLINE = true;
}

$all = findConstantsFromObject('Example');

$genders = findConstantsFromObject('Example', '/^GENDER_/');

$my_gender = 1;
$gender_name = findConstantsFromObject('Example', '/^GENDER_/', $my_gender);

if (isset($gender_name[0]))
{
    $gender_name = str_replace('GENDER_', '', key($gender_name));
}
else
{
    $gender_name = 'WTF!';
}

?>
hellekin
25-May-2010 12:07
Checking if a constant is empty is bork...

You cannot

<?php
define('A', '');
define('B', 'B');

if (empty(B)) // syntax error
if (empty(constant('B'))) // fatal error

// so instead, thanks to LawnGnome on IRC, you can cast the constants to boolean (empty string is false)
if (((boolean) A) && ((boolean) B))
  // do stuff
?>
dachnik
10-Apr-2010 03:41
You can define values in your config file using the names of your defined constants, e.g.

in your php code:
define("MY_CONST",999);

in you config file:
my = MY_CONST

When reading the file do this:

$my = constant($value); // where $value is the string "MY_CONST"

now $my holds the value of 999
roller
21-Jun-2009 12:21
howto echo CONSTANT_NAME without warnings and "if " checking:

<?php

!defined("CONSTANT_NAME") || constant("CONSTANT_NAME");

?>
cory dot mawhorter @ ephective dot com
08-Sep-2008 06:08
This is how I check to see if a bool constant is true:

<?php
function consttrue($const) {
    return !defined($const) ? false : constant($const);
}
?>

Examples
<?php
var_dump(consttrue('UNDEFINED_CONST'));

define('SOME_CONST', true);
var_dump(consttrue('SOME_CONST'));

define('SOME_CONST2', false);
var_dump(consttrue('SOME_CONST2'));
?>

Returns
bool(false)
bool(true)
bool(false)

If it isn't defined it will return false, otherwise it will return the value of the constant... which would be either true/false depending on what you set it to.
Joachim Chmielewski
15-Feb-2008 09:34
To use constants in functions additional its not neccessary to change the function call wherever you need the constant in a function.

   foo($var1);

to

    foo($var1,$const);

More easy is to change the function definition and use a default value for a new variable that contains the const value.

   function foo($var1,$my_const=CONST_VALUE){
          if($my_const==1) dosomething();
   }

Now it`s not necessary to change the function call wherever you need the function.
vgr at europeanexperts dot org
01-Mar-2007 10:57
in reply to anonymous

[quote]
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.
[/quote]

is definitely nor cleaner (because it's still as wrong as using simply "if (TRACE)") nor quicker than " if (TRACE)" (one more comparison on a boolean value). This will generate PHP errors. The constant TRACE is NOT defined.

error :
PHP Notice:  Use of undefined constant TRACE - assumed 'TRACE' in yourpath/test_constants.php on line 5

if you really want to be "clean" and as quick as possible, then there is a function :

[code]
function IsBooleanConstantAndTrue($constname) { // : Boolean
  $res=FALSE;
  if (defined($constname)) $res=(constant($constname)===TRUE);
  return($res);
}

// use : if (IsBooleanConstantAndTrue('TRACE')) echo "trace is really True<br>";
[/code]

If you want, you can see a demonstration at http://www.fecj.org/extra/test_constants.php

Regards
02-Feb-2007 02:29
@XC:

That isn't necessary. If a constant is undefined, constant() returns NULL; simply suppressing the warning should be enough:

<?php

if(defined('FOO') && constant('FOO') === 'bar'){
// ...
}

?>

becomes

<?php

if(@constant('FOO') === 'bar') {
// ...
}

?>

Note that in the first snippet, the call to constant isn't unnecessary as well, and adds a bit of overhead. If you're set on using the first notation, the following is better:

<?php

if(defined('FOO') && FOO === 'bar') {
// ...
}

?>
XC
19-Jan-2007 08:13
When you often write lines like

<?php

if(defined('FOO') && constant('FOO') === 'bar')
{
...
}

?>

to prevent errors, you can use the following function to get the value of a constant.

<?php

function getconst($const)
{
    return (defined($const)) ? constant($const) : null;
}

?>

Finally you can check the value with

<?php

if(getconst('FOO') === 'bar')
{
...
}

?>

It's simply shorter.
03-Oct-2006 09:17
If the constant does not exist, constant() will generate a warning and return null.
narada dot sage at googlemail dot com
13-Jul-2006 10:01
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 02:00
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 06:58
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 06:39
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 11:20
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 03:12
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 09:32
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 05:10
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;
}
?>

define> <connection_timeout
Last updated: Fri, 16 Jul 2010