connection_timeout
This function is namespace sensitive when calling class constants.
Using:
<?php namespace sub;
class foo {
const BAR = 'Hello World';
}
constant('foo::BAR'); // Error
constant('sub\foo::BAR'); // works
?>
This does not seem to affect constants defined with the 'define' function. Those all end up defined in the root namespace unless another namespace is implicitly defined in the string name of the constant.
constant
(PHP 4 >= 4.0.4, PHP 5)
constant — 定数の値を返す
説明
name で指定した定数の値を返します。
constant() はある定数の値を取得する必要があるが、 その名前が不明な場合に有用です。これは、定数名が変数に保存されているか、 関数により返されるかの場合です。
この関数は クラス定数に対しても動作します。
パラメータ
- name
-
定数名。
返り値
定数の値、あるいはその定数が定義されていない場合に NULL を返します。
エラー / 例外
定数が定義されていない場合は E_WARNING レベルのエラーが発生します。
例
例1 constant() の例
<?php
define("MAXSIZE", 100);
echo MAXSIZE;
echo constant("MAXSIZE"); // ひとつ前の行と同じことです
interface bar {
const test = 'foobar!';
}
class foo {
const test = 'foobar!';
}
$const = 'test';
var_dump(constant('bar::'. $const)); // string(7) "foobar!"
var_dump(constant('foo::'. $const)); // string(7) "foobar!"
?>
add a note
User Contributed Notes
constant
adam at adamhahn dot com
28-Sep-2011 12:59
Anonymous
07-Mar-2011 06:59
You can get the value of class and interface constants using this function.
<?php
interface IDatabase {
const Test = 22;
}
class MyDatabase implements IDatabase {
}
echo constant('MyDatabase::Test'); # Outputs 22
echo constant('IDatabase::Test'); # Also outputs 22
?>
bohwaz
05-Jul-2010 06:28
Return constants from an object. You can filter by regexp or match by value to find a constant name from the value.
Pretty useful sometimes.
<?php
function findConstantsFromObject($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 08:07
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
09-Apr-2010 11:41
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 $my holds the value of 999
roller
21-Jun-2009 08:21
howto echo CONSTANT_NAME without warnings and "if " checking:
<?php
!defined("CONSTANT_NAME") || constant("CONSTANT_NAME");
?>
cory dot mawhorter @ ephective dot com
08-Sep-2008 02:08
This is how I check to see if a bool constant is true:
<?php
function consttrue($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 03:34
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 05:57
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($res);
}
// use : if (IsBooleanConstantAndTrue('TRACE')) echo "trace is really True<br>";
[/code]
If you want, you can see a demonstration at http://www.fecj.org/extra/test_constants.php
Regards
01-Feb-2007 08:29
@XC:
That isn't necessary. If a constant is undefined, constant() returns NULL; simply suppressing the warning should be enough:
<?php
if(defined('FOO') && constant('FOO') === 'bar'){
// ...
}
?>
becomes
<?php
if(@constant('FOO') === 'bar') {
// ...
}
?>
Note that in the first snippet, the call to constant isn't unnecessary as well, and adds a bit of overhead. If you're set on using the first notation, the following is better:
<?php
if(defined('FOO') && FOO === 'bar') {
// ...
}
?>
XC
19-Jan-2007 02:13
When you often write lines like
<?php
if(defined('FOO') && constant('FOO') === 'bar')
{
...
}
?>
to prevent errors, you can use the following function to get the value of a constant.
<?php
function getconst($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 05:17
If the constant does not exist, constant() will generate a warning and return null.
narada dot sage at googlemail dot com
13-Jul-2006 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;
}
?>