connection_timeout
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.
constant
(PHP 4 >= 4.0.4, PHP 5)
constant — Liefert den Wert einer Konstante
Beschreibung
Gibt den Wert der durch Name angegebenen Konstante zurück.
constant() ist nützlich um den Wert einer Konstante abzufragen, deren Namen Sie nicht kennen, d.h. wenn sie in einer Variablen gespeichert ist oder von einer Funktion zurückgegeben wird.
Diese Funktion funktioniert auch mit Klassenkonstanten.
Parameter-Liste
- Name
-
Der Name der Konstante
Rückgabewerte
Gibt den Wert der Konstante zurück, oder NULL, falls die Konstante nicht definiert ist.
Beispiele
Beispiel #1 constant() Beispiel
<?php
define("MAXGROESSE", 100);
echo MAXGROESSE;
echo constant("MAXGROESSE"); // dasselbe wie in der vorigen Zeile
interface bar {
const test = 'foobar!';
}
class foo {
const test = 'foobar!';
}
$const = 'test';
var_dump(constant('bar::'. $const)); // string(7) "foobar!"
var_dump(constant('foo::'. $const)); // string(7) "foobar!"
?>
add a note
User Contributed Notesconstant
Joachim Chmielewski
15-Feb-2008 03:34
15-Feb-2008 03:34
vgr at europeanexperts dot org
01-Mar-2007 05:57
01-Mar-2007 05:57
in reply to anonymous
[quote]
To check if a constant is boolean, use this instead:
<?php
if (TRACE === true) {}
?>
Much quicker and cleaner than using defined() and constant() to check for a simple boolean.
[/quote]
is definitely nor cleaner (because it's still as wrong as using simply "if (TRACE)") nor quicker than " if (TRACE)" (one more comparison on a boolean value). This will generate PHP errors. The constant TRACE is NOT defined.
error :
PHP Notice: Use of undefined constant TRACE - assumed 'TRACE' in yourpath/test_constants.php on line 5
if you really want to be "clean" and as quick as possible, then there is a function :
[code]
function IsBooleanConstantAndTrue($constname) { // : Boolean
$res=FALSE;
if (defined($constname)) $res=(constant($constname)===TRUE);
return($res);
}
// use : if (IsBooleanConstantAndTrue('TRACE')) echo "trace is really True<br>";
[/code]
If you want, you can see a demonstration at http://www.fecj.org/extra/test_constants.php
Regards
01-Feb-2007 08:29
@XC:
That isn't necessary. If a constant is undefined, constant() returns NULL; simply suppressing the warning should be enough:
<?php
if(defined('FOO') && constant('FOO') === 'bar'){
// ...
}
?>
becomes
<?php
if(@constant('FOO') === 'bar') {
// ...
}
?>
Note that in the first snippet, the call to constant isn't unnecessary as well, and adds a bit of overhead. If you're set on using the first notation, the following is better:
<?php
if(defined('FOO') && FOO === 'bar') {
// ...
}
?>
XC
19-Jan-2007 02:13
19-Jan-2007 02:13
When you often write lines like
<?php
if(defined('FOO') && constant('FOO') === 'bar')
{
...
}
?>
to prevent errors, you can use the following function to get the value of a constant.
<?php
function getconst($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
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
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
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
$3some = 'invalid';
// This works
define('3some', 'valid');
echo constant('3some');
?>
Of course this is not a good practice, but PHP has got you covered.
timneill at hotmail dot com
26-Nov-2005 12:39
26-Nov-2005 12:39
Please note when using this function from within a class to retrieve a php5 class constant, ensure you include the 'self::'.
class Validate
{
const TEXT_MAX = 65536;
//-- this will work
public static function textWORKS($_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
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
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
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;
}
?>