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CI加载流程小结，ci加载小结
无聊，决定水一把。
CI（CodeIgniter）是我最早接触的一个框架，到现在也只是用了其中一点零碎的方法。一直想对其流程做个小结，却总是因各种各样的“理由”挨着。看见别人图表齐上阵，没那耐心，就从代码说起吧，权当做个笔记，纪念一下。
看在线的用户手册，也知道，将CI下载下来（最新版本2.2.1），解压到机子上，比如www目录，可改个根目录名（原名CodeIgniter-2.2-stable太长），初步目录文件如下，当然这在是windows下面。
访问下，如localhost/ci/index.php，就进入CI默认的Welcome页面
如何一步步加载这个页面的？首先访问的是index.php脚本
1 php
2
3 /*
4 *---------------------------------------------------------------
5 * APPLICATION ENVIRONMENT
6 *---------------------------------------------------------------
7 *
8 * You can load different configurations depending on your
9 * current environment. Setting the environment also influences
10 * things like logging and error reporting.
11 *
12 * This can be set to anything, but default usage is:
13 *
14 * development
15 * testing
16 * production
17 *
18 * NOTE: If you change these, also change the error_reporting() code below
19 *
20 */
21 define('ENVIRONMENT', 'development'
);
22 /*
23 *---------------------------------------------------------------
24 * ERROR REPORTING
25 *---------------------------------------------------------------
26 *
27 * Different environments will require different levels of error reporting.
28 * By default development will show errors but testing and live will hide them.
29 */
30
31 if (
defined('ENVIRONMENT'
))
32 {
33 switch (ENVIRONMENT)
34 {
35 case 'development':
36 error_reporting(
E_ALL);
37 break;
38
39 case 'testing':
40 case 'production':
41 error_reporting(0
);
42 break;
43
44 default:
45 exit('The application environment is not set correctly.'
);
46 }
47 }
48
49 /*
50 *---------------------------------------------------------------
51 * SYSTEM FOLDER NAME
52 *---------------------------------------------------------------
53 *
54 * This variable must contain the name of your "system" folder.
55 * Include the path if the folder is not in the same directory
56 * as this file.
57 *
58 */
59 $system_path = 'system'
;
60
61 /*
62 *---------------------------------------------------------------
63 * APPLICATION FOLDER NAME
64 *---------------------------------------------------------------
65 *
66 * If you want this front controller to use a different "application"
67 * folder then the default one you can set its name here. The folder
68 * can also be renamed or relocated anywhere on your server. If
69 * you do, use a full server path. For more info please see the user guide:
70 * http://codeigniter.com/user_guide/general/managing_apps.html
71 *
72 * NO TRAILING SLASH!
73 *
74 */
75 $application_folder = 'application'
;
76
77 /*
78 * --------------------------------------------------------------------
79 * DEFAULT CONTROLLER
80 * --------------------------------------------------------------------
81 *
82 * Normally you will set your default controller in the routes.php file.
83 * You can, however, force a custom routing by hard-coding a
84 * specific controller class/function here. For most applications, you
85 * WILL NOT set your routing here, but it's an option for those
86 * special instances where you might want to override the standard
87 * routing in a specific front controller that shares a common CI installation.
88 *
89 * IMPORTANT: If you set the routing here, NO OTHER controller will be
90 * callable. In essence, this preference limits your application to ONE
91 * specific controller. Leave the function name blank if you need
92 * to call functions dynamically via the URI.
93 *
94 * Un-comment the $routing array below to use this feature
95 *
96 */
97 // The directory name, relative to the "controllers" folder. Leave blank
98 // if your controller is not in a sub-folder within the "controllers" folder
99 // $routing['directory'] = '';
100
101 // The controller class file name. Example: Mycontroller
102 // $routing['controller'] = '';
103
104 // The controller function you wish to be called.
105 // $routing['function'] = '';
106
107
108 /*
109 * -------------------------------------------------------------------
110 * CUSTOM CONFIG VALUES
111 * -------------------------------------------------------------------
112 *
113 * The $assign_to_config array below will be passed dynamically to the
114 * config class when initialized. This allows you to set custom config
115 * items or override any default config values found in the config.php file.
116 * This can be handy as it permits you to share one application between
117 * multiple front controller files, with each file containing different
118 * config values.
119 *
120 * Un-comment the $assign_to_config array below to use this feature
121 *
122 */
123 // $assign_to_config['name_of_config_item'] = 'value of config item';
124
125
126
127 // --------------------------------------------------------------------
128 // END OF USER CONFIGURABLE SETTINGS. DO NOT EDIT BELOW THIS LINE
129 // --------------------------------------------------------------------
130
131 /*
132 * ---------------------------------------------------------------
133 * Resolve the system path for increased reliability
134 * ---------------------------------------------------------------
135 */
136
137 // Set the current directory correctly for CLI requests
138 if (
defined('STDIN'
))
139 {
140 chdir(
dirname(
__FILE__));
141 }
142
143 if (
realpath(
$system_path) !==
FALSE)
144 {
145 $system_path =
realpath(
$system_path).'/'
;
146 }
147
148 // ensure there's a trailing slash
149 $system_path =
rtrim(
$system_path, '/').'/'
;
150
151 // Is the system path correct?
152 if ( !
is_dir(
$system_path))
153 {
154 exit("Your system folder path does not appear to be set correctly. Please open the following file and correct this: ".
pathinfo(
__FILE__,
PATHINFO_BASENAME));
155 }
156
157 /*
158 * -------------------------------------------------------------------
159 * Now that we know the path, set the main path constants
160 * -------------------------------------------------------------------
161 */
162 // The name of THIS file
163 define('SELF',
pathinfo(
__FILE__,
PATHINFO_BASENAME));
164
165 // The PHP file extension
166 // this global constant is deprecated.
167 define('EXT', '.php'
);
168
169 // Path to the system folder
170 define('BASEPATH',
str_replace("\\", "/",
$system_path));
171
172 // Path to the front controller (this file)
173 define('FCPATH',
str_replace(SELF, '',
__FILE__));
174
175 // Name of the "system folder"
176 define('SYSDIR',
trim(
strrchr(
trim(BASEPATH, '/'), '/'), '/'
));
177
178
179 // The path to the "application" folder
180 if (
is_dir(
$application_folder))
181 {
182 define('APPPATH',
$application_folder.'/'
);
183 }
184 else
185 {
186 if ( !
is_dir(BASEPATH.
$application_folder.'/'
))
187 {
188 exit("Your application folder path does not appear to be set correctly. Please open the following file and correct this: ".
SELF);
189 }
190
191 define('APPPATH', BASEPATH.
$application_folder.'/'
);
192 }
193
194 /*
195 * --------------------------------------------------------------------
196 * LOAD THE BOOTSTRAP FILE
197 * --------------------------------------------------------------------
198 *
199 * And away we go...
200 *
201 */
202 require_once BASEPATH.'core/CodeIgniter.php'
;
203
204 /* End of file index.php */
205 /* Location: ./index.php */
View Code
21行：首先定义一个ENVIRONMENT常量为development，即开发环境。
31-47行：switch语句，由于当前环境是development，所以是设置报告所有级别的错误。
49-59行：$system_path变量定义CI的默认的系统脚本目录是 system，61-75行定义当前默认的供我们主要开发用的目录为 application。
77-105行：全部注释掉了，这里是我们可以强制设置系统加载时默认的目录名（$routing['directory']）、控制器名（$routing['directory']）和方法名（$routing['directory']），虽然一般这些是设置在application\config\routes.php中（下图），访问的Welcome页面也是通过这个默认控制器Welcome类进行的，这里只是作为一个选择性的方式，其实没必要弄
108-129行：全部注释掉，用于自定义配置变量（CUSTOM CONFIG VALUES），前一篇说过，任何后端project中，总有些配置信息，只是各个项目或框架加载方式不同，这个$assign_to_config数组就存放我们的自定义配置信息，如$assign_to_config['home'] = 'localhost'; ，之所以注释掉，又是因为这只是一个可选的操作，CI的用户自定义配置信息，一般放在application\config目录下边，以自动加载信息（autoload.php），普通配置信息（config.php）、常量（constants.php）、数据库（database.php）等分开文件存储，所以一般不会在这里的去配置一个要用到的变量，$assign_to_config默认是没有定义的。
从131行到index.php文件末尾主要是对一些路径变量的定义。
137-141行：是为CLI（Command-Interface Line）的调用方式准备的，是直接在Mac/Linux系统上通过终端命令运行脚本，这个在CI中文官网（http://codeigniter.org.cn/user_guide/general/cli.html）也有介绍，如果定义了名为STDIN的常量，则将执行目录改为当前文件所在目录，当然前面没有出现过STDIN这个常量的定义，这里就不会执行了。
143-155行：确定框架存放系统脚本的目录变量$system_path，也就是前面图中的system目录，这里会检测它的有效性，无效的话程序就挂在这里了。
157-192行：定义若干主要目录常量，分别是SELF：当前脚本的文件名、EXT：脚本扩展名、BASEPATH：system目录的路径、FCPATH：当前脚本所在的目录、SYSDIR：system目录的目录名，不改动的话就是system。
179-194行：定义APPPATH常量，确定application所在的目录，就是以后我们主要开发的地方，使用is_dir检测，稍微注意的是is_dir可以检测相对目录，所以实际运行的是if里边的代码，APPPATH得到的是相对路径。
最后打印看看这些变（常）量的值都是啥，有的与存放目录相关：
202行：加载BASEPATH.'core/CodeIgniter.php'脚本，就是system目录下的核心类文件目录下的文件，进入到CI的核心类目录下的文件了。
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1 if