"Fatal error: Cannot redeclare <function>"

Question

I have a function (this is exactly how it appears, from the top of my file):

<?php //dirname(getcwd()); function generate_salt() { $salt = ''; for($i = 0; $i < 19; $i++) { $salt .= chr(rand(35, 126)); } return $salt; } ...

And for some reason, I keep getting the error:

Fatal error: Cannot redeclare generate_salt() (previously declared in /Applications/MAMP/htdocs/question-air/includes/functions.php:5) in /Applications/MAMP/htdocs/question-air/includes/functions.php on line 13

I cannot figure out why or how such an error could occur. Any ideas?

Pascal MARTIN · Accepted Answer · 2009-12-23 16:37:14Z

126

This errors says your function is already defined ; which can mean :

you have the same function defined in two files
or you have the same function defined in two places in the same file
or the file in which your function is defined is included two times (so, it seems the function is defined two times)

To help with the third point, a solution would be to use include_once instead of include when including your functions.php file -- so it cannot be included more than once.

answered Dec 23, 2009 at 16:37

Pascal MARTIN

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8 Comments

Pascal MARTIN Over a year ago

Hu ; I suppose the line numbers that are indicated are not "precise" ; ; or, just as a precaution : are you sure you're looking at the "right" file ?

fishman Over a year ago

This is the only file that has a generate_salt() function.

Pascal MARTIN Over a year ago

which means that it's probably being included more than once

Pascal MARTIN Over a year ago

using include_once instead of include (and require_once instead of require) often helps, in that kind of situation : this way, it's PHP itself that makes sure a file is not included more than once

Matt07 Over a year ago

This is a brilliant answer as it covers all the possibilities. I just wanted to add a fourth one: if you are trying to define a function with the same name as a build-in class, for instance get_class, you will get the same re-declaration error.

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T.Todua · Accepted Answer · 2019-12-31 21:20:55Z

Solution 1

Don't declare function inside a loop (like foreach, for, while...) ! Declare before them.

Solution 2

You should include that file (wherein that function exists) only once. So,
instead of : include ("functions.php");
use: include_once("functions.php");

Solution 3

If none of above helps, before function declaration, add a check to avoid re-declaration:

if (!function_exists('your_function_name')) { function your_function_name() { ........ } }

Your answer pointed me in the right direction. My problem was that, though I wanted to declare a function in the global namespace, I was testing for its existence and declaring it in a specific namespace. So, we have to include the namespace of a function when we call function_exists and we should be careful where we are declaring that function.

mwfearnley · Accepted Answer · 2022-03-30 10:22:08Z

15

You can check first whether the name of your function exists or not before you declare the function:

if (!function_exists('generate_salt')) { function generate_salt() { ........ } }

OR you can change the name of the function to another name.

edited Mar 30, 2022 at 10:22

mwfearnley

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answered Nov 3, 2013 at 15:02

ahmed hamdy

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2 Comments

mwfearnley Over a year ago

I came across a function in a file that was included multiple times (to generate HTML code), so I used function_exists like you suggest, in order to make sure the function was only declared once.

Ken Lee Over a year ago

this is a very good method

codaddict · Accepted Answer · 2009-12-23 16:44:17Z

8

You're probably including the file functions.php more than once.

answered Dec 23, 2009 at 16:44

codaddict

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Comments

Community · Accepted Answer · 2017-05-23 12:10:08Z

7

In my case it was because of function inside another function! once I moved out the function, error was gone , and everything worked as expected.

This answer explains why you shouldn't use function inside function.

This might help somebody.

edited May 23, 2017 at 12:10

CommunityBot

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answered Sep 17, 2015 at 15:23

Muhammed Aslam C

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3 Comments

BSUK Over a year ago

What's wrong with including a function within a function?

David Addoteye Over a year ago

this answer helped me

mach128x Over a year ago

That was the explanation for my problem.

Roman · Accepted Answer · 2013-12-16 17:38:46Z

I had strange behavor when my *.php.bak (which automaticly was created by notepad) was included in compilation. After I removed all *.php.bak from folder this error was gone. Maybe this will be helpful for someone.

Fabio says Reinstate Monica · Accepted Answer · 2016-07-27 00:39:01Z

Another possible reason for getting that error is that your function has the same name as another PHP built-in function. For example,

function checkdate($date){ $now=strtotime(date('Y-m-d H:i:s')); $tenYearsAgo=strtotime("-10 years", $now); $dateToCheck=strtotime($date); return ($tenYearsAgo > $dateToCheck) ? false : true; } echo checkdate('2016-05-12');

where the checkdate function already exists in PHP.

Ahmad Sharif · Accepted Answer · 2022-03-31 15:05:56Z

I would like to add my 2 cent experience that might be helpful for many of you.

If you declare a function inside a loop (for, foreach, while), you will face this error message.

Jacob Bruinsma · Accepted Answer · 2019-01-22 19:20:26Z

I don't like function_exists('fun_name') because it relies on the function name being turned into a string, plus, you have to name it twice. Could easily break with refactoring.

Declare your function as a lambda expression (I haven't seen this solution mentioned):

$generate_salt = function() { ... };

And use thusly:

$salt = $generate_salt();

Then, at re-execution of said PHP code, the function simply overwrites the previous declaration.

@AlexHighHigh cool, it seemed so obvious but nobody said anything about it.
I'll elaborate on it's description at some point but for now I'm saving this in my lil magic library of useful snippets to come back to at a later date: freshlondon.biz/lambda-expression

John Parker · Accepted Answer · 2009-12-23 16:44:25Z

I'd recommend using get_included_files - as Pascal says you're either looking at the wrong file somehow or this function is already defined in a file that's been included.

require_once is also useful if the file you're attempting to include is essential.

Youssef · Accepted Answer · 2011-09-16 20:09:53Z

I had the same problem. And finally it was a double include. One include in a file named X. And another include in a file named Y. Knowing that in file Y I had include ('X')

user229044 · Accepted Answer · 2012-07-28 15:57:19Z

Since the code you've provided does not explicitly include anything, either it is being incldued twice, or (if the script is the entry point for the code) there must be a auto-prepend set up in the webserver config / php.ini or alternatively you've got a really obscure extension loaded which defines the function.

Naitik Shah · Accepted Answer · 2014-06-21 12:05:47Z

means you have already created a class with same name.

For Example:

class ExampleReDeclare {} // some code here class ExampleReDeclare {}

That second ExampleReDeclare throw the error.

Tristanisginger · Accepted Answer · 2019-10-30 16:36:35Z

If your having a Wordpress theme problem it could be because although you have renamed the theme in your wp_options table you havn't renamed the stylesheet. I struggled with this.

Brady Moritz · Accepted Answer · 2020-08-26 16:31:25Z

I had this pop up recently where a function was being called prior to its definition in the same file, and it didnt have the returned value assigned to a variable. Adding a var for the return value to be assigned to made the error go away.

happymacarts · Accepted Answer · 2021-08-25 20:52:22Z

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You have to deactivate the lite version in order to run the PRO version.

edited Aug 25, 2021 at 20:52

happymacarts

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answered Aug 25, 2021 at 3:28

Serena

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1 Comment

Paulo Over a year ago

I believe if you had any idea as to why this work. i would improve everyone's understanding of your solution.

Ameer Hamza · Accepted Answer · 2015-03-25 16:39:52Z

This errors says your function is already defined ; which can mean :

you have the same function defined in two files
or you have the same function defined in two places in the same file
or the file in which your function is defined is included two times (so, it seems the function is defined two times)

I think your facing problem at 3rd position the script including this file more than one time.So, you can solve it by using require_once instead of require or include_once instead of include for including your functions.php file -- so it cannot be included more than once.

Ruthe · Accepted Answer · 2019-08-01 02:43:02Z

or you can't create function in loop

such as

for($i=1; $i<5; $i++) { function foo() { echo 'something'; } }

foo();
//It will show error regarding redeclaration

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