CI框架源码学习笔记1——index.php

做php开发一年多了，陆陆续续用过tp/ci/yii框架，一直停留在只会使用的层面上，关于框架内部的结构实际上是不甚了解的。为了深入的学习，决定把CI框架的源码从头到尾的学习一下，

主要因为CI框架工作中用的多，而且比较轻量级，所以选择分析它，用的版本是3.1.3版本，官网可下载。

做php的都知道，项目的源头是index.php这个文件，所有的变化都是从它衍生出来，我们也先来看看这个文件。

define('ENVIRONMENT', isset($_SERVER['CI_ENV']) ? $_SERVER['CI_ENV'] : 'development');

上面的这行代码很简单，定义了ENVIRONMENT这个常量，默认定义为'development'

switch (ENVIRONMENT)
{
    case 'development':
        error_reporting(-1);
        ini_set('display_errors', 1);
    break;

    case 'testing':
    case 'production':
        ini_set('display_errors', 0);
        if (version_compare(PHP_VERSION, '5.3', '>='))
        {
            error_reporting(E_ALL & ~E_NOTICE & ~E_DEPRECATED & ~E_STRICT & ~E_USER_NOTICE & ~E_USER_DEPRECATED);
        }
        else
        {
            error_reporting(E_ALL & ~E_NOTICE & ~E_STRICT & ~E_USER_NOTICE);
        }
    break;

    default:
        header('HTTP/1.1 503 Service Unavailable.', TRUE, 503);
        echo 'The application environment is not set correctly.';
        exit(1); // EXIT_ERROR
}

根据当前的环境来设置php的一些报错信息等级什么的，分别对应开发/测试/生产环境

$system_path = 'system';
$application_folder = 'application';
$view_folder = '';

定义三个变量，没啥可说明的。

// Set the current directory correctly for CLI requests
    if (defined('STDIN'))
    {
        chdir(dirname(__FILE__));
    }

英文注释的意思是为cli设置正确的目录，网上搜了下，说是为了保证命令行模式下，ci框架可以正常运行

    if (($_temp = realpath($system_path)) !== FALSE)
    {
        $system_path = $_temp.DIRECTORY_SEPARATOR;
    }
    else
    {
        // Ensure there's a trailing slash
        $system_path = strtr(
            rtrim($system_path, '/\'),
            '/\',
            DIRECTORY_SEPARATOR.DIRECTORY_SEPARATOR
        ).DIRECTORY_SEPARATOR;
    }

返回system目录的绝对路径，我用的是ubuntu,打印出来的内容是/var/www/html/ci/system

// Is the system path correct?
    if ( ! is_dir($system_path))
    {
        header('HTTP/1.1 503 Service Unavailable.', TRUE, 503);
        echo 'Your system folder path does not appear to be set correctly. Please open the following file and correct this: '.pathinfo(__FILE__, PATHINFO_BASENAME);
        exit(3); // EXIT_CONFIG
    }

判断系统目录是否存在，如果不存在给出提示

// The name of THIS fileindex.php
    define('SELF', pathinfo(__FILE__, PATHINFO_BASENAME));//当前文件名称(index.php)

    // Path to the system directory
    define('BASEPATH', $system_path);//system文件夹路径(/var/www/html/ci/system/)

    // Path to the front controller (this file) directory
    define('FCPATH', dirname(__FILE__).DIRECTORY_SEPARATOR);//当前文件路径(/var/www/html/ci/)

    // Name of the "system" directory
    define('SYSDIR', basename(BASEPATH));//system目录名称(system)

再次定义几个常量，具体内容我写在注释里面

    // The path to the "application" directory
    if (is_dir($application_folder))
    {
        if (($_temp = realpath($application_folder)) !== FALSE)
        {
            $application_folder = $_temp;
        }
        else
        {
            $application_folder = strtr(
                rtrim($application_folder, '/\'),
                '/\',
                DIRECTORY_SEPARATOR.DIRECTORY_SEPARATOR
            );
        }
    }
    elseif (is_dir(BASEPATH.$application_folder.DIRECTORY_SEPARATOR))
    {
        $application_folder = BASEPATH.strtr(
            trim($application_folder, '/\'),
            '/\',
            DIRECTORY_SEPARATOR.DIRECTORY_SEPARATOR
        );
    }
    else
    {
        header('HTTP/1.1 503 Service Unavailable.', TRUE, 503);
        echo 'Your application folder path does not appear to be set correctly. Please open the following file and correct this: '.SELF;
        exit(3); // EXIT_CONFIG
    }

    define('APPPATH', $application_folder.DIRECTORY_SEPARATOR);

定义application目录，打印出来是/var/www/html/ci/application/

// The path to the "views" directory
    if ( ! isset($view_folder[0]) && is_dir(APPPATH.'views'.DIRECTORY_SEPARATOR))
    {
        $view_folder = APPPATH.'views';
    }
    elseif (is_dir($view_folder))
    {
        if (($_temp = realpath($view_folder)) !== FALSE)
        {
            $view_folder = $_temp;
        }
        else
        {
            $view_folder = strtr(
                rtrim($view_folder, '/\'),
                '/\',
                DIRECTORY_SEPARATOR.DIRECTORY_SEPARATOR
            );
        }
    }
    elseif (is_dir(APPPATH.$view_folder.DIRECTORY_SEPARATOR))
    {
        $view_folder = APPPATH.strtr(
            trim($view_folder, '/\'),
            '/\',
            DIRECTORY_SEPARATOR.DIRECTORY_SEPARATOR
        );
    }
    else
    {
        header('HTTP/1.1 503 Service Unavailable.', TRUE, 503);
        echo 'Your view folder path does not appear to be set correctly. Please open the following file and correct this: '.SELF;
        exit(3); // EXIT_CONFIG
    }

    define('VIEWPATH', $view_folder.DIRECTORY_SEPARATOR);

定义views目录，/var/www/html/ci/application/views/

require_once BASEPATH.'core/CodeIgniter.php';

最后，引入新文件CodeIgniter.php

我们可以看到index.php文件其实没有什么太多的内容，它的主要目的是定义一些系统需要用到的常量，以及引入新的文件CodeIgniter.php。