PHP is the first file that is loaded into a theme when a page is requested. This means that the plugin code must be loaded first so that the function is available for WordPress when the functions are loaded, the PHP file, right? One way to change the default behaviors of WordPress is to use a file called functions.php. It goes in the folder of your theme and behaves like a WordPress plugin, adding features and functionality to a WordPress site through PHP code. You can use it to call native PHP functions, WordPress functions, or to define your own functions.
Alternatively, you can place your custom PHP code in your own WordPress plugin, or simply use a functionality plugin such as the Code Snippets plugin to manage your custom PHP snippets. There are differences between using a plugin and a function php file. Each theme has its own function file, but only functions.php in the active theme affects how your site is displayed publicly. If your theme already has a feature file, you can add code to it. Otherwise, you can create a plain text file called functions.php to add to your theme's directory.
A child theme can have its own functions.php. This child function file can be used to augment or replace the functions of the parent theme. Search the web for WordPress functions.php to find suggestions to improve the functionality of your WordPress site. Since it is a PHP program, the first thing that is loaded is index.php in the root folder. This file doesn't do much by itself but defines a constant and loads the wp-blog-header.php file into the same folder. This file looks for wp-config.php if it finds one, continues the process of setting up the environment.
If there is no wp-config.php, WordPress assumes that it is a new installation and loads the installation screen. At the end of each file wp-config.php, wp-settings.php is required. This is where the real setup process begins and WordPress runs functions from load.php. These first functions are mainly used to “normalize” the server. From the comment Upload the first WordPress files, the first functions that do more than just configure things are loaded such as compat.php which adds some additional functions that are missing in previous versions of PHP. WordPress is really dedicated to supporting very old versions of PHP and class-wp.php actually builds the query, processes the query variables and configures an object that is instantiated near the end of wp-settings.php. Now plugin.php is loaded which provides the functions needed for action and filter hooks allowing you to alter the behavior of core files and plugins without touching the original code. Finally, in this series of requirements, WordPress loads mo.php to work with translation files then require_wp_db() and wp_start_object_cache() are called (from load.php) providing connections to the database and caching. They also allow you to use visits which means that you can replace default classes and functionality here. If you configure multisite in wp-config, WordPress now loads necessary functions (ms-blogs.php) and starts everything needed for multisite (ms-settings.php which is similar in concept to wp-settings). Also note that ms-settings can load a sunrise drop pin.php that can change how multisite works. The long list of requirements that follow loads all the functions and classes that give you full core functionality of WordPress such as menu creation, rights and user management etc. Each of these files justifies a blog post to cover how they work. WordPress now checks which theme is active and loads functions.php file for that theme also note that there are two additional hooks here one before selecting theme and one that runs after. The WP object now executes its init action which completes current user once this is done you get famous starter hook which lot of plugins and themes use. The entire core of WordPress functions is loaded and current user is completed. You may have thought it may never end but this really concludes wp-settings.php do you remember wp-blog-header? It requires wwp-load which requires wwp-config which in turn requires wwp-settings which loads entire WordPress API and got us to this point. Now final part of our bootstrap process all functions are available (wp-settings) and required data is loaded (wp() into functions).
Template loader then php is called (from wwp-load) this file decides which template is loaded. These features php tutorial and our free course on how to learn develop WordPress themes are all chapters of our “learn WordPress Up and Running” development guide now in its revised and expanded 3rd edition.
Autoloading Functions
What Does Autoloading Mean?
Why Autoloading Functions Is Important
How To Autoload Functions
Conclusion
Because functions.php is automatically loaded first, its functions are available anywhere in your theme's PHP files. Functions.php is a PHP file that WordPress knows how to examine as part of its “factory process”; it will ignore most filenames (such as functionz.php) by default but it knows how to open the functions of an active theme's .php, see what's inside and run it.
WordPress understands that other files in your theme may depend on functions in functions.php; this means that PHP engine needs to load functions before loading pages into template hierarchy.
Autoloading functions means that its functions are available to you in any of your theme's PHP files; as a result it's place in your theme to put calls to WordPress functions that should always be running or available; this an incredibly valuable part of WordPress theme development.
Autoloading means loading something automatically without requiring any manual intervention; when it comes to programming autoloading refers loading classes or files automatically when they are needed.
Autoloading classes or files helps reduce amount of code needed for application; instead of manually including each class or file needed for application autoloader will take care of loading them when they are needed.
Autoloading classes or files also helps keep application organized; instead having all classes or files included at beginning autoloader will only include them when they are needed.
Why autoloading functions important? Autoloading helps keep code organized; instead having all necessary code included at beginning autoloader will only include them when they are needed; this helps reduce amount code needed for application.
Autoloading also helps keep application organized; instead having all necessary code included at beginning autoloader will only include them when they are needed; this helps keep application organized by only including necessary code when it's needed.
How autoloading works? Autoloader will look for class or file name specified by programmer; if class or file found autoloader will include it; if not found autoloader will throw an error.
How autoloading works with WordPress? In order autoload classes or files with WordPress need register autoloader with spl_autoload_register(); this function takes name autoloader function as argument.
Once registered autoloader will look for class or file name specified by programmer; if class or file found autoloader will include it; if not found autoloader will throw an error.
In order use autoloader with WordPress need create custom autoloader function; this function should take class name as argument; once class name received should check if class exists; if exists should include class otherwise should throw an error.
Conclusion: Autoloading helps reduce amount code needed for application by only including necessary code when it's needed; also helps keep application organized by only including necessary code when it's needed.
Autoloading with WordPress requires registering custom autoloader with spl_autoload_register(); once registered custom autoloader should take class name as argument; if class exists should include class otherwise should throw an error.
