constant
Watch out. You can define a new constant with the name NULL with define("NULL","FOO");. But you must use the function constant("NULL"); to get it's value. NULL without the function call to the constant() function will still retrieve the special type NULL value.
Within a class there is no problem, as const NULL="Foo"; will be accessible as myClass::NULL.
define
(PHP 4, PHP 5)
define — Defines a named constant
Description
Defines a named constant at runtime.
Parameters
-
name -
The name of the constant.
-
value -
The value of the constant; only scalar and null values are allowed. Scalar values are integer, float, string or boolean values. It is possible to define resource constants, however it is not recommended and may cause unpredictable behavior.
-
case_insensitive -
If set to
TRUE, the constant will be defined case-insensitive. The default behavior is case-sensitive; i.e. CONSTANT and Constant represent different values.Note:
Case-insensitive constants are stored as lower-case.
Return Values
Returns TRUE on success or FALSE on failure.
Examples
Example #1 Defining Constants
<?php
define("CONSTANT", "Hello world.");
echo CONSTANT; // outputs "Hello world."
echo Constant; // outputs "Constant" and issues a notice.
define("GREETING", "Hello you.", true);
echo GREETING; // outputs "Hello you."
echo Greeting; // outputs "Hello you."
?>
See Also
- defined() - Checks whether a given named constant exists
- constant() - Returns the value of a constant
- The section on Constants
add a note
User Contributed Notesdefine
nl-x at bita dot nl
09-Jul-2007 07:34
09-Jul-2007 07:34
dont care
03-Jun-2007 11:19
03-Jun-2007 11:19
chris at frecod dot de, you might just use SQL for this:
NOT IN(var1,var2,var3,var4,var5,var6)
stangelanda at arrowquick dot com
01-Jan-2007 03:59
01-Jan-2007 03:59
An improvement on the function from bobbykjack at yahoo dot co dot uk on the concept by richard dot quadling at bandvulc dot co dot uk:
<?php
function adefine($constant_name, $value=null) {
static $increment = 0; // 1 for bitmask
if (is_null($value)) {
define($constant_name, ++$increment); // $increment=$increment<<1 for bitmask
} else {
define($constant_name, $value);
if (is_numeric($value)) {
$increment = $value;
}
}
}
?>
If you pass it a second argument it defines it normally, and resets the increment if the value is numeric. This way the function can replace define, and you can reset the counter for a new set of constants.
<?php
adefine ('RULE_CALLBACK_FORMAT', 1); // 1
adefine ('RULE_CHANGE_CALLBACK_ON_ERROR'); // 2
adefine ('RULE_CHANGE_COMPARE_DATE'); // 3
adefine('KEYWORD', 'hodgepodge'); // hodgepodge <-- defined normally
adefine ('RULE_CHANGE_ON_DATE'); // 4
adefine ('ERROR_DESC', 1); // 1 <-- Counter reset
adefine ('ERROR_EXPECTED_RESULT'); // 2
?>
IK
15-Nov-2005 03:42
15-Nov-2005 03:42
[Editor's Note: Obviously, constants cannot be redefined. That is the meaning of a constant.]
Just a quick note.. If a constant is once defined, any subsequent attempts to define it once again are ignored.
<?
define('WHAT_DID_YOU_EXPECT', 'First');
define('WHAT_DID_YOU_EXPECT', 'Second');
echo WHAT_DID_YOU_EXPECT
?>
Outputs 'First'.
I really thought I have gone mad when I saw just the last two lines of code (the first one was in another file) and it was echoing 'First'..
12-Feb-2005 05:45
Better pack with define() for all who really miss Java package management:
Use this "manifest.php" on very first script start or copy it to your config.somehow.php.
<?php
$__packages = array(
"org.ilove.java.more",
"org.ilove.python.too",
"net.php.isok"
);
define("C_IS_WINDOWS", false);
define("C_DIR", (C_IS_WINDOWS ? "\\" : "/"));
define("C_PATH_ROOT", str_replace("/", C_DIR, $_SERVER["DOCUMENT_ROOT"]).C_DIR);
define("C_PATH_CORE", C_PATH_ROOT."core".C_DIR);
define("C_PATH_CLASS", C_PATH_CORE."classes".C_DIR);
define("C_APPLICATION_BASE", C_PATH_CORE.C_DIR."application".C_DIR);
$total_packages = 0;
$i = sizeof($__packages);
while($i-- > 0) {
$tokens = explode(".", $__packages[$i]);
$j = sizeof($tokens);
while($j-- > 0) {
$token = strtolower(trim($tokens[$j]));
if(strlen($token) > 0 && !defined($token)) {
define($token, ($j == 0 ? C_PATH_CLASS : "").$tokens[$j].C_DIR);
$total_packages++;
}
}
}
define("C_PACKAGE_COUNT", $total_packages);
?>
With restrictions on non-package constants, you now can call your files like that:
<?php
require_once org.ilove.java.more."Than.php";
?>
Regards
Robi
phpnet at trenkner dot de
15-Mar-2003 12:59
15-Mar-2003 12:59
---[Editor's Note]---
As of PHP 5.0.0 this is possible. You can define class-only constants, which can be called like Foo::Constant1 from the outside
---[End Note]---
Please keep in mind that
class AClass {
define ("Const1", "Value1");
... }
didn't work. You have to make all your constant definitions before you open the class. So
define ("Const1", "Value1");
class AClass {
... }
would be correct.
radovan dot biciste at managestar dot com
07-Nov-2001 05:45
07-Nov-2001 05:45
Wonder how to work with variable which name is stored in a constant?
Here it is:
<?php
define("VAR_NAME","test");
// assigning value
${VAR_NAME} = "value";
// getting value back
echo ${VAR_NAME};
?>
ste at opk dot no
29-Aug-2001 07:41
29-Aug-2001 07:41
To use a constant to show an element of an array inside a string:
define ('C', 0); print ("element 0: {$a[C]}");
The { & } around the variable signals that what's inside should be treated as a variable and not a string.
Note that 'print ("a constant:{C}");' wont work as ZERO is a constant.