Loading... In this tutorial you will learn how to include and evaluate the files in PHP. ## Including a PHP File into Another PHP File The include() and require() statement allow you to include the code contained in a PHP file within another PHP file. Including a file produces the same result as copying the script from the file specified and pasted into the location where it is called. You can save a lot of time and work through including files — Just store a block of code in a separate file and include it wherever you want using the include() and require() statements instead of typing the entire block of code multiple times. A typical example is including the header, footer and menu file within all the pages of a website. The basic syntax of the include() and require() statement can be given with: ```php include("path/to/filename"); -Or- include "path/to/filename"; require("path/to/filename"); -Or- require "path/to/filename"; ``` > Tip: Like the print and echo statements, you can omit the parentheses while using the include and require statements as demonstrated above. The following example will show you how to include the common header, footer and menu codes which are stored in separate ‘header.php’, ‘footer.php’ and ‘menu.php’ files respectively, within all the pages of your website. Using this technique you can update all pages of the website at once by making the changes to just one file, this saves a lot of repetitive work. ```php <!DOCTYPE html> <html lang="en"> <head> <title>Tutorial Republic</title> </head> <body> <?php include "header.php"; ?> <?php include "menu.php"; ?> <h1>Welcome to Our Website!</h1> <p>Here you will find lots of useful information.</p> <?php include "footer.php"; ?> </body> </html> ``` ## Difference Between include and require Statements You might be thinking if we can include files using the include() statement then why we need require(). Typically the require() statement operates like include(). The only difference is — the include() statement will only generate a PHP warning but allow script execution to continue if the file to be included can’t be found, whereas the require() statement will generate a fatal error and stops the script execution. 你可能会想，如果我们可以使用include()语句来包含文件，那么我们为什么需要require()。通常require()语句的操作类似于include()。 唯一的区别是——如果找不到要包含的文件，include()语句只会生成一个PHP警告，但允许脚本继续执行，而require()语句将生成一个致命错误并停止脚本执行。 ```php <?php require "my_variables.php"; ?> <?php require "my_functions.php"; ?> <!DOCTYPE html> <html lang="en"> <head> <title><?php displayTitle($home_page); ?></title> </head> <body> <?php include "header.php"; ?> <?php include "menu.php"; ?> <h1>Welcome to Our Website!</h1> <p>Here you will find lots of useful information.</p> <?php include "footer.php"; ?> </body> </html> ``` > Tip: It is recommended to use the require() statement if you’re including the library files or files containing the functions and configuration variables that are essential for running your application, such as database configuration file. ## The include\_once and require\_once Statements If you accidentally include the same file (typically functions or classes files) more than one time within your code using the include or require statements, it may cause conflicts. To prevent this situation, PHP provides include\_once and require\_once statements. These statements behave in the same way as include and require statements with one exception. The include\_once and require\_once statements will only include the file once even if asked to include it a second time i.e. if the specified file has already been included in a previous statement, the file is not included again. To better understand how it works, let’s check out an example. Suppose we’ve a my\_functions.php file with the following code: ```php <?php function multiplySelf($var){ $var *= $var; // multiply variable by itself echo $var; } ?> ``` Here’s the PHP script within which we’ve included the my\_functions.php file. ```php <?php // Including file require "my_functions.php"; // Calling the function multiplySelf(2); // Output: 4 echo "<br>"; // Including file once again require "my_functions.php"; // Calling the function multiplySelf(5); // Doesn't execute ?> ``` When you run the above script, you will see the error message something like this: “Fatal error: Cannot redeclare multiplySelf()”. This occurs because the my\_functions.php included twice, this means the function multiplySelf() is defined twice, which caused PHP to stop script execution and generate fatal error. Now rewrite the above example with require\_once. ```php <?php // Including file require_once "my_functions.php"; // Calling the function multiplySelf(2); // Output: 4 echo "<br>"; // Including file once again require_once "my_functions.php"; // Calling the function multiplySelf(5); // Output: 25 ?> ``` Last modification：September 10, 2024 © Allow specification reprint Like 如果觉得我的文章对你有用，请随意赞赏