通过分析WP的代码来学习PHP。1

下载了WP的代码，并且应用到了网站上面，现在也在正常的运行中，地址是：www.freealgorithm.tk 。具体的申请过程就不赘述了，学习WP的代码。

他的目录结构就不看了，可以下载同名文件我会通过相对目录来区分。

进入网站的第一个默认的页面：/index.php

<?php

/**
 * Front to the WordPress application. This file doesn't do anything, but loads
 * wp-blog-header.php which does and tells WordPress to load the theme.
 *
 * @package WordPress
 */

/**
 * Tells WordPress to load the WordPress theme and output it.
 *
 * @var bool

*/

define('WP_USE_THEMES', true);

/** Loads the WordPress Environment and Template */
 #定义WP_USE_THEMES为true
require( dirname( __FILE__ ) . '/wp-blog-header.php' );
 #返回路径中目录部分并且连接字符串得到此php文件的位置，用这个文件代替这个位置
#引入同目录下的wp-blog-header.php文件

知识点：define函数，bool define    ( string $name   , mixed $value   [, bool $case_insensitive = false  ] ) 成功返回true否则false。
name：常量的名字。value：常量的值；仅允许标量和 null。标量的类型是 integer，float，string 或者 boolean。 也能够定义常量值的类型为 resource ，但并不推荐这么做，可能会导致未知状况的发生。

require函数替换参数指向的文件，__FILE__取得当前文件的绝对路径，dirname返回路径中的目录部分。比如这个文件返回的就是根目录/。'.'这个符号是字符串连接运算符，将dirname(__FILE__)返回的字符串与'/wp-blog-header.php'相连接然后require进去。

而/wp-blog-header.php这个文件被包含了，如下：

 <?php

 /**
  * Loads the WordPress environment and template.
  载入WordPress的环境和模板*
  * @package WordPress
  */

 if ( !isset($wp_did_header) ) #变量是否定义，定义返回true
 {

     $wp_did_header = true;

     require_once( dirname(__FILE__) . '/wp-load.php' );

     #用wp-load.php代替此语句
     /*如果定义了就不继续执行，否则执行下面的语句    */

     wp();

     require_once( ABSPATH . WPINC . '/template-loader.php' );

 #同样用
 }

isset函数用来判断这个变量是否已经被定义了，如果定义了就返回true否则返回false。如果没有定义的话就执行下面的语句，$wp_did_header=true;是定义变量，他是一个布尔变量。然后require_once这个文件 ,require_once函数与require的区别是以后再这个文件里不能再包含这个文件了，即仅仅包含这个文件一次。这些的动作是定义一个布尔变量且包含一个文件。下面的wp();函数指行，现在不知道这个函数的作用，一会就会看到。然后继续包含ABSPATH.WPINC.'/template-loader.php'。这个文件了。ABSPATH是绝对路径的意思，这个是WP自定义的常量，还有WPINC这两个，现在我们也不知道它的值是什么。此文件到此没有结束，我们继续跟踪进入wp-load.php.

 <?php

 /**

  * Bootstrap file for setting the ABSPATH constant
  * and loading the wp-config.php file. The wp-config.php
  * file will then load the wp-settings.php file, which
  * will then set up the WordPress environment.
  *
  * If the wp-config.php file is not found then an error
  * will be displayed asking the visitor to set up the
  * wp-config.php file.
  *
  * Will also search for wp-config.php in WordPress' parent
  * directory to allow the WordPress directory to remain
  * untouched.
  *
  * @internal This file must be parsable by PHP4.
  *
  * @package WordPress
  */

 /** Define ABSPATH as this file's directory
 */

 define( 'ABSPATH', dirname(__FILE__) . '/' );

 error_reporting( E_CORE_ERROR | E_CORE_WARNING | E_COMPILE_ERROR | E_ERROR | E_WARNING | E_PARSE | E_USER_ERROR | E_USER_WARNING | E_RECOVERABLE_ERROR );

 /*error_reporting() 函数能够在运行时设置 error_reporting 指令。 PHP 有诸多错误级别，使用该函数可以设置在脚本运行时的级别。 如果没有设置可选参数 level， error_reporting() 仅会返回当前的错误报告级别。 */

 if ( file_exists( ABSPATH . 'wp-config.php') ) #file_exists — 检查文件或目录是否存在，绝对路径+'wp-config.php'检测是否存在，这个文件是设置文件，后来在网站文件上传完成后进行安装时候来创建，所以在没有安装时候是不存在这个文件的。
 {

     /** The config file resides in ABSPATH */

     require_once( ABSPATH . 'wp-config.php' );

 #如果文件存在，require_once把文件拿来
 #如果文件不存在，判断绝对路径取

 } elseif ( file_exists( dirname(ABSPATH) . '/wp-config.php' ) && ! file_exists( dirname(ABSPATH) . '/wp-settings.php' ) )
 {

     /** The config file resides one level above ABSPATH but is not part of another install */

     require_once( dirname(ABSPATH) . '/wp-config.php' );

 } else {

     // A config file doesn't exist

     define( 'WPINC', 'wp-includes' );

     define( 'WP_CONTENT_DIR', ABSPATH . 'wp-content' );

     require_once( ABSPATH . WPINC . '/load.php' );

     require_once( ABSPATH . WPINC . '/version.php' );

     wp_check_php_mysql_versions();

     wp_load_translations_early();

     // Standardize $_SERVER variables across setups.

     wp_fix_server_vars();

     require_once( ABSPATH . WPINC . '/functions.php' );

     $path = wp_guess_url() . '/wp-admin/setup-config.php';

     // Die with an error message

     $die  = __( "There doesn't seem to be a <code>wp-config.php</code> file. I need this before we can get started." ) . '</p>';

     $die .= '<p>' . __( "Need more help? <a href='http://codex.wordpress.org/Editing_wp-config.php'>We got it</a>." ) . '</p>';

     $die .= '<p>' . __( "You can create a <code>wp-config.php</code> file through a web interface, but this doesn't work for all server setups. The safest way is to manually create the file." ) . '</p>';
     $die .= '<p><a href="' . $path . '" class="button button-large">' . __( "Create a Configuration File" ) . '</a>';

     wp_die( $die, __( 'WordPress &rsaquo; Error' ) );
 }

代码稍长，但是以后的代码会更长。这里看到了他的注释说定义ABSPATH为当前文件的目录，而且看到了这个define语句，知道了ABSPATH是dirname(__FILE__).'/'。其实还是这个根目录。error_reporting函数的说明在代码里面注释着意思是定义错误级别，我在书中也没有看到类似的说明这个函数，现在不予理会。
if当前绝对路径下的  /wp-config.php文件存在的话就require这个文件。不存在的话继续判断（/wp-config.php和/wp-settings.php）文件是否不存在，那么判断wp-config.php这个文件的判断是否多余？wp-setting.php这个文件是存在的，而wp-config.php是后来在安装时后生成的，第一次安装使用时候是没有的。否则就定义WPINC为'wp-includes'，define( 'WP_CONTENT_DIR', ABSPATH . 'wp-content' );require_once( ABSPATH . WPINC . '/load.php' );这句是将 /wp-includes/load.php包含进去，require_once( ABSPATH . WPINC . '/version.php' );这句将/wp-includes/version.php包含进去。先跟踪进去/wp-includes/load.php。

 <?php

 /**
  * These functions are needed to load WordPress.
  *
  * @internal This file must be parsable by PHP4.
  *
  * @package WordPress
  */

 /**
  * Turn register globals off.
  *
  * @access private
  * @since 2.1.0
  * @return null Will return null if register_globals PHP directive was disabled
  */

 function wp_unregister_GLOBALS()
 {

     if ( !ini_get( 'register_globals' ) )

         return;

     if ( isset( $_REQUEST['GLOBALS'] ) )

         die( 'GLOBALS overwrite attempt detected' );

     // Variables that shouldn't be unset

     $no_unset = array( 'GLOBALS', '_GET', '_POST', '_COOKIE', '_REQUEST', '_SERVER', '_ENV', '_FILES', 'table_prefix' );

     $input = array_merge( $_GET, $_POST, $_COOKIE, $_SERVER, $_ENV, $_FILES, isset( $_SESSION ) && is_array( $_SESSION ) ? $_SESSION : array() );
     foreach ( $input as $k => $v )

         if ( !in_array( $k, $no_unset ) && isset( $GLOBALS[$k] ) )
         {

             unset( $GLOBALS[$k] );

         }

 }

 /**
  * Fix $_SERVER variables for various setups.
  *
  * @access private
  * @since 3.0.0
  */

 function wp_fix_server_vars()
 {

     global $PHP_SELF;

     $default_server_values = array(

         'SERVER_SOFTWARE' => '',

         'REQUEST_URI' => '',

     );

     $_SERVER = array_merge( $default_server_values, $_SERVER );

     // Fix for IIS when running with PHP ISAPI

     if ( empty( $_SERVER['REQUEST_URI'] ) || ( php_sapi_name() != 'cgi-fcgi' && preg_match( '/^Microsoft-IIS\//', $_SERVER['SERVER_SOFTWARE'] ) ) )
     {

         // IIS Mod-Rewrite

         if ( isset( $_SERVER['HTTP_X_ORIGINAL_URL'] ) )
         {

             $_SERVER['REQUEST_URI'] = $_SERVER['HTTP_X_ORIGINAL_URL'];

         }
         // IIS Isapi_Rewrite

         else if ( isset( $_SERVER['HTTP_X_REWRITE_URL'] ) ) {

             $_SERVER['REQUEST_URI'] = $_SERVER['HTTP_X_REWRITE_URL'];

         } else {
             // Use ORIG_PATH_INFO if there is no PATH_INFO

             if ( !isset( $_SERVER['PATH_INFO'] ) && isset( $_SERVER['ORIG_PATH_INFO'] ) )

                 $_SERVER['PATH_INFO'] = $_SERVER['ORIG_PATH_INFO'];

             // Some IIS + PHP configurations puts the script-name in the path-info (No need to append it twice)

             if ( isset( $_SERVER['PATH_INFO'] ) ) {

                 if ( $_SERVER['PATH_INFO'] == $_SERVER['SCRIPT_NAME'] )

                     $_SERVER['REQUEST_URI'] = $_SERVER['PATH_INFO'];

                 else

                     $_SERVER['REQUEST_URI'] = $_SERVER['SCRIPT_NAME'] . $_SERVER['PATH_INFO'];
                         }    

             // Append the query string if it exists and isn't null

             if ( ! empty( $_SERVER['QUERY_STRING'] ) ) {

                 $_SERVER['REQUEST_URI'] .= '?' . $_SERVER['QUERY_STRING'];

             }

         }

     }

     // Fix for PHP as CGI hosts that set SCRIPT_FILENAME to something ending in php.cgi for all requests

     if ( isset( $_SERVER['SCRIPT_FILENAME'] ) && ( strpos( $_SERVER['SCRIPT_FILENAME'], 'php.cgi' ) == strlen( $_SERVER['SCRIPT_FILENAME'] ) - 7 ) )

         $_SERVER['SCRIPT_FILENAME'] = $_SERVER['PATH_TRANSLATED'];

     // Fix for Dreamhost and other PHP as CGI hosts

     if ( strpos( $_SERVER['SCRIPT_NAME'], 'php.cgi' ) !== false )

         unset( $_SERVER['PATH_INFO'] );

     // Fix empty PHP_SELF

     $PHP_SELF = $_SERVER['PHP_SELF'];

     if ( empty( $PHP_SELF ) )

         $_SERVER['PHP_SELF'] = $PHP_SELF = preg_replace( '/(\?.*)?$/', '', $_SERVER["REQUEST_URI"] );

 }

 /**
  * Check for the required PHP version, and the MySQL extension or a database drop-in.
  *
  * Dies if requirements are not met.
  *
  * @access private
  * @since 3.0.0
  */

 function wp_check_php_mysql_versions() {

     global $required_php_version, $wp_version;

     $php_version = phpversion();

     if ( version_compare( $required_php_version, $php_version, '>' ) ) {

         wp_load_translations_early();

         header( 'Content-Type: text/html; charset=utf-8' );

         die( sprintf( __( 'Your server is running PHP version %1$s but WordPress %2$s requires at least %3$s.' ), $php_version, $wp_version, $required_php_version ) );

     }

     if ( ! extension_loaded( 'mysql' ) && ! extension_loaded( 'mysqli' ) && ! file_exists( WP_CONTENT_DIR . '/db.php' ) ) {

         wp_load_translations_early();

         header( 'Content-Type: text/html; charset=utf-8' );

         die( __( 'Your PHP installation appears to be missing the MySQL extension which is required by WordPress.' ) );

     }

 }

 /**
  * Don't load all of WordPress when handling a favicon.ico request.
  * Instead, send the headers for a zero-length favicon and bail.
  *
  * @since 3.0.0
  */

 function wp_favicon_request() {

     if ( '/favicon.ico' == $_SERVER['REQUEST_URI'] ) {

         header('Content-Type: image/vnd.microsoft.icon');

         header('Content-Length: 0');

         exit;

     }

 }

 /**
  * Dies with a maintenance message when conditions are met.
  *
  * Checks for a file in the WordPress root directory named ".maintenance".
  * This file will contain the variable $upgrading, set to the time the file
  * was created. If the file was created less than 10 minutes ago, WordPress
  * enters maintenance mode and displays a message.
  *
  * The default message can be replaced by using a drop-in (maintenance.php in
  * the wp-content directory).
  *
  * @access private
  * @since 3.0.0
  */

 function wp_maintenance() {

     if ( !file_exists( ABSPATH . '.maintenance' ) || defined( 'WP_INSTALLING' ) )

         return;

     global $upgrading;

     include( ABSPATH . '.maintenance' );

     // If the $upgrading timestamp is older than 10 minutes, don't die.

     if ( ( time() - $upgrading ) >= 600 )

         return;

     if ( file_exists( WP_CONTENT_DIR . '/maintenance.php' ) ) {

         require_once( WP_CONTENT_DIR . '/maintenance.php' );

         die();

     }

     wp_load_translations_early();

     $protocol = $_SERVER["SERVER_PROTOCOL"];

     if ( 'HTTP/1.1' != $protocol && 'HTTP/1.0' != $protocol )

         $protocol = 'HTTP/1.0';

     header( "$protocol 503 Service Unavailable", true, 503 );

     header( 'Content-Type: text/html; charset=utf-8' );

     header( 'Retry-After: 600' );

 ?>

这是load.php的php部分，下面就基本是html代码了，html先不予分析。ini_get返回配制选项的值