The core function of PHP files is to handle dynamic web content, combining server-side logic and front-end display. A typical structure includes four steps: introducing configuration files, starting a session, loading an autoloader, and routing and distribution. PHP allows dynamic content to be embedded in HTML, suitable for building template pages, but it is recommended to use the template engine to separate logic from views. In the file introduction method, require is used to ensure that the script terminates in errors, and include is used for optional modules; it is recommended to use the _once version uniformly to prevent duplicate loading. The code organization recommends a separate file for each class, and classifies functions into tool classes or services, and uses namespaces to improve readability and automatic loading efficiency.

The core function of PHP files is to handle dynamic web content and combine server-side logic with front-end display. A typical PHP file not only contains HTML code, but also embeds dynamic functions such as variables, conditional judgment, loop structure, and database interaction. Its structure looks simple, but it carries complete web application logic behind it.

Basic file structure: start from the entrance

Most PHP projects have a main entry file, such as index.php , which is responsible for loading the configuration, initializing the framework, and starting the request processing process.

Typical structures may include:

• Introduce configuration files (such as config.php )
• Start the session (session_start())
• Loading the autoloader (Composer's autoload.php)
• Routing distribution or controller call

For example:

 <?php
require_once &#39;config.php&#39;;
session_start();
require_once &#39;vendor/autoload.php&#39;;

$router = new Router();
$router->dispatch();

Although this structure is short, it clearly divides the different stages of program startup, making it easy to maintain and expand.

Why do you need to mix HTML and PHP?

One of the original design goals of PHP was to enable developers to easily embed dynamic content in HTML. Therefore, you often see writing styles like this:

 <h1>Welcome, <?php echo $username; ?></h1>

This approach is great for building template pages. Of course, it is recommended to use template engines (such as Twig or Blade) in actual development to separate logic and views to improve readability and maintainability.

It should be noted that when writing mixed writing, you should avoid writing too much business logic in HTML, otherwise it will cause bloat and difficult to maintain.

The difference between inclusion and introduction: include or require?

PHP provides four ways to import external files: include , include_once , require and require_once .

Their differences are mainly in error handling:

• include : If the file does not exist, only a warning will be generated and the script will continue to be executed
• require : If the file does not exist, a fatal error will be generated and the script will stop executing

So usually:

• Configuration files and core library use require_once
• Optional modules or templates can be include

It is recommended to use the _once version uniformly to prevent duplicate loading from causing problems.

How functions and classes are organized

A PHP file can define only one class, or it can contain multiple functions or be used in a mixed manner. However, for better readability and compliance with PSR specifications, it is recommended:

• A separate file for each class
• Try to classify functions into tool classes or encapsulate them into services
• Organize code levels using namespace

For example:

 // File path: App/Controllers/UserController.php
namespace App\Controllers;

class UserController {
    public function showProfile($id) {
        // ...
    }
}

This clear structure is also conducive to the automatic loading mechanism to identify the classpath.

Basically that's it. Understanding the structure and purpose of PHP files will help write more standardized and easy-to-maintain code.

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