unset or change a defined constant PHP

Question

assumed i define a variable like this:

<?php
define("page", "actual-page");
?>

now i have to change this content from actual-page to second-page how can i realize that?

i try the following methods:

<?php
// method 1
    page = "second-page";

// method 2
    define("page", "second-page");

// method 3
    unset(page);
    define("page", "second-page");
?>

now my ideas goes out... what can i do else?

As Juampi answered, by using `define()` you're setting a constant, 'page'. Instead, use a variable: `$page = 'actual-page';`. — Jamie Schembri, May 11 '13 at 12:53
The definition of "constant": _[noun] A situation that does not change._ You should use a variable instead. — BadHorsie, Dec 19 '19 at 14:34

Juan Pablo Rinaldi · Accepted Answer · 2013-05-11T12:47:03.620

21

When you use PHP's define() function, you're not defining a variable, you're defining a constant. Constants can't have their value modified once the script starts executing.

edited May 11 '13 at 12:47

answered May 11 '13 at 12:35

Juan Pablo Rinaldi

3,394
1
20
20

so... change a defined variable is impossible? – Alex Ruhl May 11 '13 at 12:46
7

To make it ultra clear: You CAN change a VARIABLE's value during execution. You CANNOT change a CONSTANT's value during execution. – Juan Pablo Rinaldi May 11 '13 at 12:52
yea! this is what i mean! thanks! and sry that i write `variable` and not `constant`! – Alex Ruhl May 11 '13 at 12:55

Cobra_Fast · Answer 2 · 2014-07-22T13:02:08.643

6

You can, with the runkit PECL extension:

runkit_constant_remove('page');

http://php.net/runkit_constant_remove
http://github.com/zenovich/runkit

sudo pecl install https://github.com/downloads/zenovich/runkit/runkit-1.0.3.tgz

Update: This module seems to cause trouble with various other things, like the session system for example.

edited Jul 22 '14 at 13:02

answered Jul 22 '14 at 12:20

Cobra_Fast

15,671
8
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score 4 · Answer 3 · answered Jul 06 '18 at 09:01

4

Maybe a very late answer, but the question was "now my ideas goes out... what can i do else?"

Here is what you can do "else" - use $GLOBALS:

<?php
// method 1
    $GLOBALS['page'] = 'first-page';

// method 2
    $GLOBALS['page'] = "second-page";

// method 3
    $GLOBALS['page'] = 'third-page';
?>

I hope it helps. I use it when I do imports and I want specific events not to be fired if the import flag is on for example :)

answered Jul 06 '18 at 09:01

Mihai Pop

65
6

1

`$GLOBALS['page']` is for variable `$page`, instead of constant `page`. – LianSheng Nov 24 '20 at 16:02

score -15 · Answer 4 · answered Aug 12 '16 at 10:53

-15

define has a third argument (boolean) which override the first defined constant to the second defined constant. Setting the first defined constant to true.

<?php
define("page", "actual-page", true);
// Returns page = actual-page

define("page", "second-page");
// Returns page = second-page
?>

answered Aug 12 '16 at 10:53

Shudmeyer

354
2
14

8

The third argument is whether the constant should be case sensitive, not whether it can be redefined. http://php.net/manual/en/function.define.php – Matt van Andel Sep 21 '16 at 19:52
ditto Matt's comment. – Rich R Nov 29 '22 at 00:50

unset or change a defined constant PHP

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