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PHP: how to avoid redeclaring functions?

Posted by: admin April 23, 2020 Leave a comment


I tend to get errors such as:

Fatal error: Cannot redeclare get_raw_data_list() (previously declared in /var/www/codes/handlers/make_a_thread/get_raw_data_list.php:7) in /var/www/codes/handlers/make_a_thread/get_raw_data_list.php on line 19

how can I avoid the error? Is it possible to create a IF-clause to check whether a function is declared before declaring it?

How to&Answers:

Use require_once or include_once as opposed to include or require when including the files that contain your functions.

The _once siblings of include and require will force PHP to check if the file has already been included/required, and if so, not include/require it again, thereby preventing ‘cannot redeclare x function…‘ fatal errors.


if(!function_exists("get_raw_data_list")) {
... define function here ...



function_exists” will tell you if a function has already been declared. Though I suspect maybe you have a problem with including files more than once. When you include a file are you using require_once or include_once or just require / include?


If you are dealing with Classes method_exists() might be what you’re looking for:

if(!method_exists(__CLASS__, 'function_name')){
    function function_name(){


This will check the current Class to make that the function function_name doesn’t exist before trying to declare it