You can store your constant as the value of a variable like this:
$variable=VARIABLE;
To access the constant, do this: constant($variable).
Beware: if your variable changes, then you loose your reference to the constant - but the constant itself will not change.
I've found this especially useful for storing the constant string (i.e. VARIABLE) in a database.
define
(PHP 4, PHP 5)
define — 名前を指定して定数を定義する
パラメータ
返り値
成功した場合に TRUE を、失敗した場合に FALSE を返します。
例
例1 定数の定義
<?php
define("CONSTANT", "Hello world.");
echo CONSTANT; // "Hello world." を出力します
echo Constant; // "Constant" を出力し、警告が発生します
define("GREETING", "Hello you.", true);
echo GREETING; // "Hello you." を出力します
echo Greeting; // "Hello you." を出力します
?>
define
jason@sitehatchery dot com
25-Apr-2008 03:28
25-Apr-2008 03:28
rayro at gmx dot de
16-Sep-2007 06:53
16-Sep-2007 06:53
just a note to the previous post by e s lin d sey at g mail dot co m:
Well as u said, it is not the best workaround. To resolve this "Problem" without getting incredible loss of performance, you are able to make the use of "variable functions" like "variable variables":
<?php
$def = 'constant';
$string = <<<END
This is PHP running on<br />
{$def('PHP_OS')}
END;
var_dump($string);
?>
In this example we make use of the "constant" function which is builtin, and it will output:
string(37) " This is PHP running on
WINNT"
Tested on PHP 5...
Best regards
e s lin d sey at g mail dot co m
14-Aug-2007 05:38
14-Aug-2007 05:38
Constants can't be referenced from within quotes or (more importantly IMHO) from within HEREDOC syntax. This is a huge drawback in my opinion. Here's two of my workarounds:
<?php
//PHP5 only -- more efficient
$constarray = get_defined_constants(true);
foreach($constarray['user'] as $key => $val)
eval(sprintf('$_CONSTANTS[\'%s\'] = \'%s\';', addslashes($key), addslashes($val)));
//PHP4+ -- less efficient because it defines (potentially) hundreds of unnecessary constants
foreach(get_defined_constants() as $key => $val)
eval(sprintf('$_CONSTANTS[\'%s\'] = \'%s\';', addslashes($key), addslashes($val)));
?>
Now you can refer to your defined constants using the $_CONSTANTS array. Note that because this is NOT a superglobal, a few caveats apply:
<?php
//run code snippet here to define $_CONSTANTS in global scope...
$mv = $_CONSTANTS['FOO']; //works
function my_function1()
{
$mv = $_CONSTANTS['BAR']; //doesn't work! not defined!
}
function my_function2()
{
global $_CONSTANTS;
$mv = $_CONSTANTS['BAR']; //ah, this works!
}
?>
I realize this is not ideal, either for performance or for convenience of being able to refer to constants without regard to scope, but it is a workaround that works. Depending on your application, it may be easier to shift your paradigm a bit and use the following method instead, declaring your constants as variables first:
<?php
//first, define our constants...
$_CONSTANTS['FOO'] = 'bar';
$_CONSTANTS['BAR'] = 'foo';
//now, turn them into real constants...
foreach($_CONSTANTS as $key => $val)
define($key, $val);
//now, you can use either format to refer to a constant
print($_CONSTANTS['FOO']); //prints 'bar'
print(FOO); //prints 'bar'
print("$_CONSTANTS['FOO']"); //prints 'bar'
//prints 'blah bar blah'
print <<<EOF
blah {$_CONSTANTS['FOO']} blah
EOF;
?>
Hope this helps some of you out there, I know being able to utilize my constants in HEREDOC helped me a ton!
smifffy at smith-net dot org dot uk
26-Jul-2007 08:23
26-Jul-2007 08:23
a basic function to auto assign a numeric value that increase by itself each time - used in some permission style scripts
<?php
function define_bitwise($constant_name, $reset = False)
{
static $bitwise_next = 1;
if ( $reset === True )
{
$bitwise_next = 1;
}
define($constant_name, $bitwise_next);
$bitwise_next += $bitwise_next;
}
?>
when reset it set to True, resets that value to 1 and starts afresh
creeves at dja dot com
19-Jul-2007 10:59
19-Jul-2007 10:59
Intersting to note:
I found this in php5 on windows
If you try to unset a constant (which you cant but maybe you have a Jr. programmer or something). The error message that is thrown is:
<?php
define ("SOME_CONSTANT", true);
unset (SOME_CONSTANT);
?>
Parse error: parse error, unexpected ')', expecting T_PAAMAYIM_NEKUDOTAYIM
nl-x at bita dot nl
10-Jul-2007 02:34
10-Jul-2007 02:34
Watch out. You can define a new constant with the name NULL with define("NULL","FOO");. But you must use the function constant("NULL"); to get it's value. NULL without the function call to the constant() function will still retrieve the special type NULL value.
Within a class there is no problem, as const NULL="Foo"; will be accessible as myClass::NULL.
stangelanda at arrowquick dot com
01-Jan-2007 11:59
01-Jan-2007 11:59
An improvement on the function from bobbykjack at yahoo dot co dot uk on the concept by richard dot quadling at bandvulc dot co dot uk:
<?php
function adefine($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
?>
12-Feb-2005 01:45
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 08:59
15-Mar-2003 08:59
---[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 01:45
07-Nov-2001 01:45
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 ${VAR_NAME};
?>
ste at opk dot no
30-Aug-2001 02:41
30-Aug-2001 02:41
To use a constant to show an element of an array inside a string:
define ('C', 0); print ("element 0: {$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.