主要关注红色标记语句即可。

The include (or require) statement takes all the text/code/markup that exists in the specified file and copies it into the file that uses the include statement.

Including files is very useful when you want to include the same PHP, HTML, or text on multiple pages of a website.

PHP include and require Statements

It is possible to insert the content of one PHP file into another PHP file (before the server executes it), with the include or require statement.

The include and require statements are identical, except upon failure:

• require will produce a fatal error (E_COMPILE_ERROR) and stop the script
• include will only produce a warning (E_WARNING) and the script will continue

So, if you want the execution to go on and show users the output, even if the include file is missing, use the include statement. Otherwise, in case of FrameWork, CMS, or a complex PHP application coding, always use the require statement to include a key file to the flow of execution. This will help avoid compromising your application‘s security and integrity, just in-case one key file is accidentally missing.

Including files saves a lot of work. This means that you can create a standard header, footer, or menu file for all your web pages. Then, when the header needs to be updated, you can only update the header include file.

Syntax

PHP include Examples

Example 1

Assume we have a standard footer file called "footer.php", that looks like this:

To include the footer file in a page, use the include statement:

Example 2

Assume we have a standard menu file called "menu.php":

All pages in the Web site should use this menu file. Here is how it can be done (we are using a <div> element so that the menu easily can be styled with CSS later):

Example 3

Assume we have a file called "vars.php", with some variables defined:

Then, if we include the "vars.php" file, the variables can be used in the calling file:

PHP include vs. require

The require statement is also used to include a file into the PHP code.

However, there is one big difference between include and require; when a file is included with the include statement and PHP cannot find it, the script will continue to execute:

If we do the same example using the require statement, the echo statement will not be executed because the script execution dies after the require statement returned a fatal error:

	Use require when the file is required by the application. Use include when the file is not required and application should continue when file is not found.