constant

Returns the value of a constant (PHP 4 >= 4.0.4, PHP 5)
mixed constant ( string name )

Example 1351. constant() example

copy to clipboard

<?php


define("MAXSIZE", 100);


echo MAXSIZE;

echo constant("MAXSIZE"); // same thing as the previous line

?>

Related Examples ( Source code ) » constant

Examples ( Source code ) » Class Constant

Examples ( Source code ) » Define class constant

Examples ( Source code ) » Define class level constant value to control the class behaviour

Examples ( Source code ) » PHP provides a couple of constants especially for use as Booleans

Examples ( Source code ) » Boolean type constant

Examples ( Source code ) » Defining a Constant

Code Examples / Notes » constant

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.

narada dot sage

To access the value of a class constant use the following technique. <?php class a { const b = 'c'; } echo constant('a::b'); // output: c ?>

joachim kruyswijk

The constant name can be an empty string. Code: define("", "foo"); echo constant(""); Output: foo

trevor blackbird > yurab.com

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

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); } }

andre

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; } ?>

service

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

11-oct-2005 03:20

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.

vgr

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 "; [/code] If you want, you can see a demonstration at http://www.fecj.org/extra/test_constants.php Regards

04-oct-2006 01:17

If the constant does not exist, constant() will generate a warning and return null.

vgr_experts_exchange

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'))) {} ?>

02-feb-2007 04:29

@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') { // ... } ?>

Change Language

connection_aborted
connection_status
connection_timeout
constant
define
defined
die
eval
exit
get_browser
__halt_compiler
highlight_file
highlight_string
ignore_user_abort
pack
php_check_syntax
php_strip_whitespace
show_source
sleep
sys_getloadavg
time_nanosleep
time_sleep_until
uniqid
unpack
usleep