我們開始分析Codeigniter的第一支檔案：index.php。
一個Codeigniter網站，全部的http request都會經過index.php這支檔案，所以網址總是類似 /index.php?controller/method 這樣。
（實務上通常會用.htaccess之類的設定檔將index.php從網址內移除 。）
幾乎所有的web framework都有類似的實作，此為
Front Controller Pattern。
/*
*---------------------------------------------------------------
* APPLICATION ENVIRONMENT
*---------------------------------------------------------------
*
* You can load different configurations depending on your
* current environment. Setting the environment also influences
* things like logging and error reporting.
*
* This can be set to anything, but default usage is:
*
* development
* testing
* production
*
* NOTE: If you change these, also change the error_reporting() code below
*/
define('ENVIRONMENT', 'development');
/*
*---------------------------------------------------------------
* ERROR REPORTING
*---------------------------------------------------------------
*
* Different environments will require different levels of error reporting.
* By default development will show errors but testing and live will hide them.
*/
switch (ENVIRONMENT)
{
case 'development':
// error_reporting(-1);
error_reporting();
ini_set('display_errors', 1);
break;
case 'testing':
case 'production':
error_reporting(-1);
ini_set('display_errors', 0);
break;
default:
header('HTTP/1.1 503 Service Unavailable.', TRUE, 503);
exit('The application environment is not set correctly.');
}
首先定義ENVIRONMENT常數。利用它辨認目前網站處於開發、測試、還是正式上線狀態。
系統在這裡利用它決定顯示多少錯誤訊息，在之後也會利用它決定要連哪個資料庫。
你可以在任何地方使用這個常數。
初學者常會覺得CI預設的報錯訊息不夠多。上網找到PHP相關函數之後，可以將它們寫在這裡。
/*
*---------------------------------------------------------------
* SYSTEM FOLDER NAME
*---------------------------------------------------------------
*
* This variable must contain the name of your "system" folder.
* Include the path if the folder is not in the same directory
* as this file.
*/
$system_path = 'system';
/*
*---------------------------------------------------------------
* APPLICATION FOLDER NAME
*---------------------------------------------------------------
*
* If you want this front controller to use a different "application"
* folder then the default one you can set its name here. The folder
* can also be renamed or relocated anywhere on your server. If
* you do, use a full server path. For more info please see the user guide:
* http://codeigniter.com/user_guide/general/managing_apps.html
*
* NO TRAILING SLASH!
*/
$application_folder = 'application';
/*
*---------------------------------------------------------------
* VIEW FOLDER NAME
*---------------------------------------------------------------
*
* If you want to move the view folder out of the application
* folder set the path to the folder here. The folder can be renamed
* and relocated anywhere on your server. If blank, it will default
* to the standard location inside your application folder. If you
* do move this, use the full server path to this folder.
*
* NO TRAILING SLASH!
*/
$view_folder = '';
/*
* --------------------------------------------------------------------
* DEFAULT CONTROLLER
* --------------------------------------------------------------------
*
* Normally you will set your default controller in the routes.php file.
* You can, however, force a custom routing by hard-coding a
* specific controller class/function here. For most applications, you
* WILL NOT set your routing here, but it's an option for those
* special instances where you might want to override the standard
* routing in a specific front controller that shares a common CI installation.
*
* IMPORTANT: If you set the routing here, NO OTHER controller will be
* callable. In essence, this preference limits your application to ONE
* specific controller. Leave the function name blank if you need
* to call functions dynamically via the URI.
*
* Un-comment the $routing array below to use this feature
*/
// The directory name, relative to the "controllers" folder. Leave blank
// if your controller is not in a sub-folder within the "controllers" folder
// $routing['directory'] = '';
// The controller class file name. Example: Mycontroller
// $routing['controller'] = '';
// The controller function you wish to be called.
// $routing['function'] = '';
/*
* -------------------------------------------------------------------
* CUSTOM CONFIG VALUES
* -------------------------------------------------------------------
*
* The $assign_to_config array below will be passed dynamically to the
* config class when initialized. This allows you to set custom config
* items or override any default config values found in the config.php file.
* This can be handy as it permits you to share one application between
* multiple front controller files, with each file containing different
* config values.
*
* Un-comment the $assign_to_config array below to use this feature
*/
// $assign_to_config['name_of_config_item'] = 'value of config item';
// --------------------------------------------------------------------
// END OF USER CONFIGURABLE SETTINGS. DO NOT EDIT BELOW THIS LINE
// --------------------------------------------------------------------
/*
* ---------------------------------------------------------------
* Resolve the system path for increased reliability
* ---------------------------------------------------------------
*/
// Set the current directory correctly for CLI requests
if (defined('STDIN'))
{
chdir(dirname(__FILE__));
}
if (realpath($system_path) !== FALSE)
{
$system_path = realpath($system_path).'/';
}
// ensure there's a trailing slash
$system_path = rtrim($system_path, '/').'/';
// Is the system path correct?
if ( ! is_dir($system_path))
{
exit('Your system folder path does not appear to be set correctly. Please open the following file and correct this: '.pathinfo(__FILE__, PATHINFO_BASENAME));
}
這意這邊的幾個PHP內建函式。defined, realpath, is_dir, rtrim都十分好用。
Codeigniter有支援從command line的操作（譬如你可以用CI寫幾支任務，再透過Linux的crontab去定期「戳」它來達到排程效果。），
如果STDIN常數有被定義的話，代表是來自command line而非http request的操作，調整php到當前執行資料夾。
STDIN常數參考這裡
接著注意下面一個coding技巧：為了確保最後有'/'字元，可能要寫幾個if / else。這邊用rtrim函式，一行就完成。
注意這行：chdir(dirname(__FILE__));。
移動到當前檔案所在的資料夾？那不就是移動到原地？
為什麼要針對command line input寫這行？
這行是多餘的？
/*
* -------------------------------------------------------------------
* Now that we know the path, set the main path constants
* -------------------------------------------------------------------
*/
// The name of THIS file
define('SELF', pathinfo(__FILE__, PATHINFO_BASENAME));
// The PHP file extension
// this global constant is deprecated.
define('EXT', '.php');
// Path to the system folder
define('BASEPATH', str_replace('\\', '/', $system_path));
// Path to the front controller (this file)
define('FCPATH', str_replace(SELF, '', __FILE__));
// Name of the "system folder"
define('SYSDIR', trim(strrchr(trim(BASEPATH, '/'), '/'), '/'));
// The path to the "application" folder
if (is_dir($application_folder))
{
define('APPPATH', $application_folder.'/');
}
else
{
if ( ! is_dir(BASEPATH.$application_folder.'/'))
{
header('HTTP/1.1 503 Service Unavailable.', TRUE, '503');
exit('Your application folder path does not appear to be set correctly. Please open the following file and correct this: '.SELF);
}
define('APPPATH', BASEPATH.$application_folder.'/');
}
// The path to the "views" folder
if (is_dir($view_folder))
{
define ('VIEWPATH', $view_folder .'/');
}
else
{
if ( ! is_dir(APPPATH.'views/'))
{
header('HTTP/1.1 503 Service Unavailable.', TRUE, '503');
exit('Your view folder path does not appear to be set correctly. Please open the following file and correct this: '.SELF);
}
define ('VIEWPATH', APPPATH.'views/' );
}
/*
* --------------------------------------------------------------------
* LOAD THE BOOTSTRAP FILE
* --------------------------------------------------------------------
*
* And away we go...
*/
require_once BASEPATH.'core/CodeIgniter.php';
/* End of file index.php */
/* Location: ./index.php */
這邊定義幾個整個framework會用到的常數，並檢查必要的application、system資料夾是否存在。
其實CI的使用者根本不應該讓application、system這種資料夾不見。
這邊相關的錯誤訊息提示是一種defensive programming，可以說是一種貼心的提醒，這也是CI對新手友善的原因之一吧。
最後一行引入core/Codeigniter.php，整個framework的精華正式開始。
分析core/Codeigniter.php