{"id":896,"date":"2021-04-06T02:33:18","date_gmt":"2021-04-06T02:33:18","guid":{"rendered":"https:\/\/phptutorial.net\/?page_id=896"},"modified":"2025-04-06T07:50:14","modified_gmt":"2025-04-06T07:50:14","slug":"php-include_once","status":"publish","type":"page","link":"https:\/\/www.phptutorial.net\/php-tutorial\/php-include_once\/","title":{"rendered":"PHP include_once"},"content":{"rendered":"\n

Summary<\/strong>: in this tutorial, you will learn how to use the PHP include_once<\/code> construct to include a file once.<\/p>\n\n\n\n

Introduction to the PHP include_once construct #<\/a><\/h2>\n\n\n\n

In the include<\/a><\/code> tutorial, you learned how to load the code from another file using the include<\/code> construct.<\/p>\n\n\n\n

Sometimes, you may have a file that is included more than once.<\/p>\n\n\n\n

If the included file has a function, you’ll get a fatal error because the function is already redeclared in the first load. For example:<\/p>\n\n\n\n

Suppose that you have the following project directory:<\/p>\n\n\n

.\n\u251c\u2500\u2500 inc\n\u2502   \u2514\u2500\u2500 functions.php\n\u2514\u2500\u2500 index.php<\/code><\/span>Code language:<\/span> plaintext<\/span> (<\/span>plaintext<\/span>)<\/span><\/small><\/pre>\n\n\n
The functions.php<\/code> has the dd()<\/code> function definition:<\/p>\n\n\n
<?php<\/span>\n\nfunction<\/span> dd<\/span>($data)<\/span>\n<\/span>{\n\techo<\/span> '<pre>'<\/span>;\n\tvar_dump($data);\n\techo<\/span> '<\/pre>'<\/span>;\n\tdie<\/span>();\n}<\/code><\/span>Code language:<\/span> PHP<\/span> (<\/span>php<\/span>)<\/span><\/small><\/pre>\n\n\n
And in the index.php file<\/code>, you include the functions.php<\/code> file twice:<\/p>\n\n\n
<?php<\/span>\n\ninclude<\/span> 'inc\/functions.php'<\/span>;\ninclude<\/span> 'inc\/functions.php'<\/span>;<\/code><\/span>Code language:<\/span> PHP<\/span> (<\/span>php<\/span>)<\/span><\/small><\/pre>\n\n\n
PHP will issue the following error if you run the index.php<\/code> file:<\/p>\n\n\n
Fatal error: Cannot redeclare dd() (previously declared in .\\inc\\functions.php:3) in .\\inc\\functions.php on line 3<\/code><\/span>Code language:<\/span> plaintext<\/span> (<\/span>plaintext<\/span>)<\/span><\/small><\/pre>\n\n\n
Likewise, if the included file outputs some HTML elements, you’ll see them more once on the page. To see how it happens, let’s create two new files header.php<\/code> and footer.php<\/code> in the inc<\/code> directory:<\/p>\n\n\n\n
header.php<\/code><\/p>\n\n\n
<!DOCTYPE html>\n<html lang=\"en\"<\/span>>\n\t<head>\n\t\t<meta charset=\"UTF-8\"<\/span> \/>\n\t\t<meta name=\"viewport\"<\/span> content=\"width=device-width, initial-scale=1.0\"<\/span> \/>\n\t\t<title>PHP include_once<\/span><\/title>\n\t<\/head>\n\t<body><\/code><\/span>Code language:<\/span> PHP<\/span> (<\/span>php<\/span>)<\/span><\/small><\/pre>\n\n\n
footer.php<\/code><\/p>\n\n\n
<\/body>\n<\/html><\/code><\/span>Code language:<\/span> PHP<\/span> (<\/span>php<\/span>)<\/span><\/small><\/pre>\n\n\n
In the index.php<\/code> file, if you include the header.php<\/code> file twice, you’ll see that the page will have two headers:<\/p>\n\n\n
<?php<\/span> include<\/span> 'inc\/header.php'<\/span> ?><\/span>\n<?php<\/span> include<\/span> 'inc\/header.php'<\/span> ?><\/span>\n\n<h1>PHP include_once<\/span> Demo<\/h1>\n\n\n<?php<\/span> include<\/span> 'inc\/footer.php'<\/span> ?><\/span><\/code><\/span>Code language:<\/span> PHP<\/span> (<\/span>php<\/span>)<\/span><\/small><\/pre>\n\n\n
To avoid including a file more than once, you can use the include_once<\/code> statement:<\/p>\n\n\n
include_once<\/span> 'path_to_file'<\/span>;<\/code><\/span>Code language:<\/span> PHP<\/span> (<\/span>php<\/span>)<\/span><\/small><\/pre>\n\n\n
The include_once<\/code> behaves like the include<\/code> statement except that if the file is included again, the include_once<\/code> won’t load the file and returns true<\/code>.<\/p>\n\n\n\n
Simply put, the include_once<\/code> loads the file just once, regardless of how many times the file is included.<\/p>\n\n\n\n
In the example above, if you use the include_once<\/code> construct, the script will work properly:<\/p>\n\n\n
<?php<\/span> include_once<\/span> 'inc\/header.php'<\/span> ?><\/span>\n<?php<\/span> include_once<\/span> 'inc\/header.php'<\/span> ?><\/span>\n\n<h1>PHP include_once<\/span> Demo<\/h1>\n\n<?php<\/span> include_once<\/span> 'inc\/footer.php'<\/span> ?><\/span><\/code><\/span>Code language:<\/span> PHP<\/span> (<\/span>php<\/span>)<\/span><\/small><\/pre>\n\n\n
Why use the PHP include_once construct #<\/a><\/h2>\n\n\n\n
Image that you have a file called index.php<\/code> that loads two other files:<\/p>\n\n\n\n