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
<span> 1</span> <?<span>php
</span><span> 2</span>
<span> 3</span> <span>/*</span>
<span> 4</span> <span> *---------------------------------------------------------------
</span><span> 5</span> <span> * APPLICATION ENVIRONMENT
</span><span> 6</span> <span> *---------------------------------------------------------------
</span><span> 7</span> <span> *
</span><span> 8</span> <span> * You can load different configurations depending on your
</span><span> 9</span> <span> * current environment. Setting the environment also influences
</span><span> 10</span> <span> * things like logging and error reporting.
</span><span> 11</span> <span> *
</span><span> 12</span> <span> * This can be set to anything, but default usage is:
</span><span> 13</span> <span> *
</span><span> 14</span> <span> * development
</span><span> 15</span> <span> * testing
</span><span> 16</span> <span> * production
</span><span> 17</span> <span> *
</span><span> 18</span> <span> * NOTE: If you change these, also change the error_reporting() code below
</span><span> 19</span> <span> *
</span><span> 20</span> <span>*/</span>
<span> 21</span> <span>define</span>('ENVIRONMENT', 'development'<span>);
</span><span> 22</span> <span>/*</span>
<span> 23</span> <span> *---------------------------------------------------------------
</span><span> 24</span> <span> * ERROR REPORTING
</span><span> 25</span> <span> *---------------------------------------------------------------
</span><span> 26</span> <span> *
</span><span> 27</span> <span> * Different environments will require different levels of error reporting.
</span><span> 28</span> <span> * By default development will show errors but testing and live will hide them.
</span><span> 29</span> <span>*/</span>
<span> 30</span>
<span> 31</span> <span>if</span> (<span>defined</span>('ENVIRONMENT'<span>))
</span><span> 32</span> <span>{
</span><span> 33</span> <span>switch</span><span> (ENVIRONMENT)
</span><span> 34</span> <span> {
</span><span> 35</span> <span>case</span> 'development':
<span> 36</span> <span>error_reporting</span>(<span>E_ALL</span><span>);
</span><span> 37</span> <span>break</span><span>;
</span><span> 38</span>
<span> 39</span> <span>case</span> 'testing':
<span> 40</span> <span>case</span> 'production':
<span> 41</span> <span>error_reporting</span>(0<span>);
</span><span> 42</span> <span>break</span><span>;
</span><span> 43</span>
<span> 44</span> <span>default</span>:
<span> 45</span> <span>exit</span>('The application environment is not set correctly.'<span>);
</span><span> 46</span> <span> }
</span><span> 47</span> <span>}
</span><span> 48</span>
<span> 49</span> <span>/*</span>
<span> 50</span> <span> *---------------------------------------------------------------
</span><span> 51</span> <span> * SYSTEM FOLDER NAME
</span><span> 52</span> <span> *---------------------------------------------------------------
</span><span> 53</span> <span> *
</span><span> 54</span> <span> * This variable must contain the name of your "system" folder.
</span><span> 55</span> <span> * Include the path if the folder is not in the same directory
</span><span> 56</span> <span> * as this file.
</span><span> 57</span> <span> *
</span><span> 58</span> <span>*/</span>
<span> 59</span> <span>$system_path</span> = 'system'<span>;
</span><span> 60</span>
<span> 61</span> <span>/*</span>
<span> 62</span> <span> *---------------------------------------------------------------
</span><span> 63</span> <span> * APPLICATION FOLDER NAME
</span><span> 64</span> <span> *---------------------------------------------------------------
</span><span> 65</span> <span> *
</span><span> 66</span> <span> * If you want this front controller to use a different "application"
</span><span> 67</span> <span> * folder then the default one you can set its name here. The folder
</span><span> 68</span> <span> * can also be renamed or relocated anywhere on your server. If
</span><span> 69</span> <span> * you do, use a full server path. For more info please see the user guide:
</span><span> 70</span> <span> * http://codeigniter.com/user_guide/general/managing_apps.html
</span><span> 71</span> <span> *
</span><span> 72</span> <span> * NO TRAILING SLASH!
</span><span> 73</span> <span> *
</span><span> 74</span> <span>*/</span>
<span> 75</span> <span>$application_folder</span> = 'application'<span>;
</span><span> 76</span>
<span> 77</span> <span>/*</span>
<span> 78</span> <span> * --------------------------------------------------------------------
</span><span> 79</span> <span> * DEFAULT CONTROLLER
</span><span> 80</span> <span> * --------------------------------------------------------------------
</span><span> 81</span> <span> *
</span><span> 82</span> <span> * Normally you will set your default controller in the routes.php file.
</span><span> 83</span> <span> * You can, however, force a custom routing by hard-coding a
</span><span> 84</span> <span> * specific controller class/function here. For most applications, you
</span><span> 85</span> <span> * WILL NOT set your routing here, but it's an option for those
</span><span> 86</span> <span> * special instances where you might want to override the standard
</span><span> 87</span> <span> * routing in a specific front controller that shares a common CI installation.
</span><span> 88</span> <span> *
</span><span> 89</span> <span> * IMPORTANT: If you set the routing here, NO OTHER controller will be
</span><span> 90</span> <span> * callable. In essence, this preference limits your application to ONE
</span><span> 91</span> <span> * specific controller. Leave the function name blank if you need
</span><span> 92</span> <span> * to call functions dynamically via the URI.
</span><span> 93</span> <span> *
</span><span> 94</span> <span> * Un-comment the $routing array below to use this feature
</span><span> 95</span> <span> *
</span><span> 96</span> <span>*/</span>
<span> 97</span> <span>//</span><span> The directory name, relative to the "controllers" folder. Leave blank
</span><span> 98</span> <span> // if your controller is not in a sub-folder within the "controllers" folder
</span><span> 99</span> <span> // $routing['directory'] = '';
</span><span>100</span>
<span>101</span> <span> // The controller class file name. Example: Mycontroller
</span><span>102</span> <span> // $routing['controller'] = '';
</span><span>103</span>
<span>104</span> <span> // The controller function you wish to be called.
</span><span>105</span> <span> // $routing['function'] = '';</span>
<span>106</span>
<span>107</span>
<span>108</span> <span>/*</span>
<span>109</span> <span> * -------------------------------------------------------------------
</span><span>110</span> <span> * CUSTOM CONFIG VALUES
</span><span>111</span> <span> * -------------------------------------------------------------------
</span><span>112</span> <span> *
</span><span>113</span> <span> * The $assign_to_config array below will be passed dynamically to the
</span><span>114</span> <span> * config class when initialized. This allows you to set custom config
</span><span>115</span> <span> * items or override any default config values found in the config.php file.
</span><span>116</span> <span> * This can be handy as it permits you to share one application between
</span><span>117</span> <span> * multiple front controller files, with each file containing different
</span><span>118</span> <span> * config values.
</span><span>119</span> <span> *
</span><span>120</span> <span> * Un-comment the $assign_to_config array below to use this feature
</span><span>121</span> <span> *
</span><span>122</span> <span>*/</span>
<span>123</span> <span>//</span><span> $assign_to_config['name_of_config_item'] = 'value of config item';
</span><span>124</span>
<span>125</span>
<span>126</span>
<span>127</span> <span>// --------------------------------------------------------------------
</span><span>128</span> <span>// END OF USER CONFIGURABLE SETTINGS. DO NOT EDIT BELOW THIS LINE
</span><span>129</span> <span>// --------------------------------------------------------------------</span>
<span>130</span>
<span>131</span> <span>/*</span>
<span>132</span> <span> * ---------------------------------------------------------------
</span><span>133</span> <span> * Resolve the system path for increased reliability
</span><span>134</span> <span> * ---------------------------------------------------------------
</span><span>135</span> <span>*/</span>
<span>136</span>
<span>137</span> <span>//</span><span> Set the current directory correctly for CLI requests</span>
<span>138</span> <span>if</span> (<span>defined</span>('STDIN'<span>))
</span><span>139</span> <span> {
</span><span>140</span> <span>chdir</span>(<span>dirname</span>(<span>__FILE__</span><span>));
</span><span>141</span> <span> }
</span><span>142</span>
<span>143</span> <span>if</span> (<span>realpath</span>(<span>$system_path</span>) !== <span>FALSE</span><span>)
</span><span>144</span> <span> {
</span><span>145</span> <span>$system_path</span> = <span>realpath</span>(<span>$system_path</span>).'/'<span>;
</span><span>146</span> <span> }
</span><span>147</span>
<span>148</span> <span>//</span><span> ensure there's a trailing slash</span>
<span>149</span> <span>$system_path</span> = <span>rtrim</span>(<span>$system_path</span>, '/').'/'<span>;
</span><span>150</span>
<span>151</span> <span>//</span><span> Is the system path correct?</span>
<span>152</span> <span>if</span> ( ! <span>is_dir</span>(<span>$system_path</span><span>))
</span><span>153</span> <span> {
</span><span>154</span> <span>exit</span>("Your system folder path does not appear to be set correctly. Please open the following file and correct this: ".<span>pathinfo</span>(<span>__FILE__</span>,<span> PATHINFO_BASENAME));
</span><span>155</span> <span> }
</span><span>156</span>
<span>157</span> <span>/*</span>
<span>158</span> <span> * -------------------------------------------------------------------
</span><span>159</span> <span> * Now that we know the path, set the main path constants
</span><span>160</span> <span> * -------------------------------------------------------------------
</span><span>161</span> <span>*/</span>
<span>162</span> <span>//</span><span> The name of THIS file</span>
<span>163</span> <span>define</span>('SELF', <span>pathinfo</span>(<span>__FILE__</span>,<span> PATHINFO_BASENAME));
</span><span>164</span>
<span>165</span> <span>//</span><span> The PHP file extension
</span><span>166</span> <span> // this global constant is deprecated.</span>
<span>167</span> <span>define</span>('EXT', '.php'<span>);
</span><span>168</span>
<span>169</span> <span>//</span><span> Path to the system folder</span>
<span>170</span> <span>define</span>('BASEPATH', <span>str_replace</span>("\\", "/", <span>$system_path</span><span>));
</span><span>171</span>
<span>172</span> <span>//</span><span> Path to the front controller (this file)</span>
<span>173</span> <span>define</span>('FCPATH', <span>str_replace</span>(SELF, '', <span>__FILE__</span><span>));
</span><span>174</span>
<span>175</span> <span>//</span><span> Name of the "system folder"</span>
<span>176</span> <span>define</span>('SYSDIR', <span>trim</span>(<span>strrchr</span>(<span>trim</span>(BASEPATH, '/'), '/'), '/'<span>));
</span><span>177</span>
<span>178</span>
<span>179</span> <span>//</span><span> The path to the "application" folder</span>
<span>180</span> <span>if</span> (<span>is_dir</span>(<span>$application_folder</span><span>))
</span><span>181</span> <span> {
</span><span>182</span> <span>define</span>('APPPATH', <span>$application_folder</span>.'/'<span>);
</span><span>183</span> <span> }
</span><span>184</span> <span>else</span>
<span>185</span> <span> {
</span><span>186</span> <span>if</span> ( ! <span>is_dir</span>(BASEPATH.<span>$application_folder</span>.'/'<span>))
</span><span>187</span> <span> {
</span><span>188</span> <span>exit</span>("Your application folder path does not appear to be set correctly. Please open the following file and correct this: ".<span>SELF);
</span><span>189</span> <span> }
</span><span>190</span>
<span>191</span> <span>define</span>('APPPATH', BASEPATH.<span>$application_folder</span>.'/'<span>);
</span><span>192</span> <span> }
</span><span>193</span>
<span>194</span> <span>/*</span>
<span>195</span> <span> * --------------------------------------------------------------------
</span><span>196</span> <span> * LOAD THE BOOTSTRAP FILE
</span><span>197</span> <span> * --------------------------------------------------------------------
</span><span>198</span> <span> *
</span><span>199</span> <span> * And away we go...
</span><span>200</span> <span> *
</span><span>201</span> <span>*/</span>
<span>202</span> <span>require_once</span> BASEPATH.'core/CodeIgniter.php'<span>;
</span><span>203</span>
<span>204</span> <span>/*</span><span> End of file index.php </span><span>*/</span>
<span>205</span> <span>/*</span><span> Location: ./index.php </span><span>*/</span>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。
=====================================================================================================
<span> 1</span> <?php <span>if</span> ( ! <span>defined</span>('BASEPATH')) <span>exit</span>('No direct script access allowed'<span>);
</span><span> 2</span> <span>/*</span><span>*
</span><span> 3</span> <span> * CodeIgniter
</span><span> 4</span> <span> *
</span><span> 5</span> <span> * An open source application development framework for PHP 5.1.6 or newer
</span><span> 6</span> <span> *
</span><span> 7</span> <span> * @package CodeIgniter
</span><span> 8</span> <span> * @author EllisLab Dev Team
</span><span> 9</span> <span> * @copyright Copyright (c) 2008 - 2014, EllisLab, Inc.
</span><span> 10</span> <span> * @copyright Copyright (c) 2014 - 2015, British Columbia Institute of Technology (http://bcit.ca/)
</span><span> 11</span> <span> * @license http://codeigniter.com/user_guide/license.html
</span><span> 12</span> <span> * @link http://codeigniter.com
</span><span> 13</span> <span> * @since Version 1.0
</span><span> 14</span> <span> * @filesource
</span><span> 15</span> <span>*/</span>
<span> 16</span>
<span> 17</span> <span>//</span><span> ------------------------------------------------------------------------</span>
<span> 18</span>
<span> 19</span> <span>/*</span><span>*
</span><span> 20</span> <span> * System Initialization File
</span><span> 21</span> <span> *
</span><span> 22</span> <span> * Loads the base classes and executes the request.
</span><span> 23</span> <span> *
</span><span> 24</span> <span> * @package CodeIgniter
</span><span> 25</span> <span> * @subpackage codeigniter
</span><span> 26</span> <span> * @category Front-controller
</span><span> 27</span> <span> * @author EllisLab Dev Team
</span><span> 28</span> <span> * @link http://codeigniter.com/user_guide/
</span><span> 29</span> <span>*/</span>
<span> 30</span>
<span> 31</span> <span>/*</span><span>*
</span><span> 32</span> <span> * CodeIgniter Version
</span><span> 33</span> <span> *
</span><span> 34</span> <span> * @var string
</span><span> 35</span> <span> *
</span><span> 36</span> <span>*/</span>
<span> 37</span> <span>define</span>('CI_VERSION', '2.2.1'<span>);
</span><span> 38</span>
<span> 39</span> <span>/*</span><span>*
</span><span> 40</span> <span> * CodeIgniter Branch (Core = TRUE, Reactor = FALSE)
</span><span> 41</span> <span> *
</span><span> 42</span> <span> * @var boolean
</span><span> 43</span> <span> *
</span><span> 44</span> <span>*/</span>
<span> 45</span> <span>define</span>('CI_CORE', <span>FALSE</span><span>);
</span><span> 46</span>
<span> 47</span> <span>/*</span>
<span> 48</span> <span> * ------------------------------------------------------
</span><span> 49</span> <span> * Load the global functions
</span><span> 50</span> <span> * ------------------------------------------------------
</span><span> 51</span> <span>*/</span>
<span> 52</span> <span>require</span>(BASEPATH.'core/Common.php'<span>);
</span><span> 53</span>
<span> 54</span> <span>/*</span>
<span> 55</span> <span> * ------------------------------------------------------
</span><span> 56</span> <span> * Load the framework constants
</span><span> 57</span> <span> * ------------------------------------------------------
</span><span> 58</span> <span>*/</span>
<span> 59</span> <span>if</span> (<span>defined</span>('ENVIRONMENT') AND <span>file_exists</span>(APPPATH.'config/'.ENVIRONMENT.'/constants.php'<span>))
</span><span> 60</span> <span> {
</span><span> 61</span> <span>require</span>(APPPATH.'config/'.ENVIRONMENT.'/constants.php'<span>);
</span><span> 62</span> <span> }
</span><span> 63</span> <span>else</span>
<span> 64</span> <span> {
</span><span> 65</span> <span>require</span>(APPPATH.'config/constants.php'<span>);
</span><span> 66</span> <span> }
</span><span> 67</span>
<span> 68</span> <span>/*</span>
<span> 69</span> <span> * ------------------------------------------------------
</span><span> 70</span> <span> * Define a custom error handler so we can log PHP errors
</span><span> 71</span> <span> * ------------------------------------------------------
</span><span> 72</span> <span>*/</span>
<span> 73</span> <span>set_error_handler</span>('_exception_handler'<span>);
</span><span> 74</span>
<span> 75</span> <span>if</span> ( ! is_php('5.3'<span>))
</span><span> 76</span> <span> {
</span><span> 77</span> @<span>set_magic_quotes_runtime</span>(0); <span>//</span><span> Kill magic quotes</span>
<span> 78</span> <span> }
</span><span> 79</span>
<span> 80</span> <span>/*</span>
<span> 81</span> <span> * ------------------------------------------------------
</span><span> 82</span> <span> * Set the subclass_prefix
</span><span> 83</span> <span> * ------------------------------------------------------
</span><span> 84</span> <span> *
</span><span> 85</span> <span> * Normally the "subclass_prefix" is set in the config file.
</span><span> 86</span> <span> * The subclass prefix allows CI to know if a core class is
</span><span> 87</span> <span> * being extended via a library in the local application
</span><span> 88</span> <span> * "libraries" folder. Since CI allows config items to be
</span><span> 89</span> <span> * overriden via data set in the main index. php file,
</span><span> 90</span> <span> * before proceeding we need to know if a subclass_prefix
</span><span> 91</span> <span> * override exists. If so, we will set this value now,
</span><span> 92</span> <span> * before any classes are loaded
</span><span> 93</span> <span> * Note: Since the config file data is cached it doesn't
</span><span> 94</span> <span> * hurt to load it here.
</span><span> 95</span> <span>*/</span>
<span> 96</span> <span>if</span> (<span>isset</span>(<span>$assign_to_config</span>['subclass_prefix']) AND <span>$assign_to_config</span>['subclass_prefix'] != ''<span>)
</span><span> 97</span> <span> {
</span><span> 98</span> get_config(<span>array</span>('subclass_prefix' => <span>$assign_to_config</span>['subclass_prefix'<span>]));
</span><span> 99</span> <span> }
</span><span>100</span>
<span>101</span> <span>/*</span>
<span>102</span> <span> * ------------------------------------------------------
</span><span>103</span> <span> * Set a liberal script execution time limit
</span><span>104</span> <span> * ------------------------------------------------------
</span><span>105</span> <span>*/</span>
<span>106</span> <span>if</span> (<span>function_exists</span>("set_time_limit") == <span>TRUE</span> AND @<span>ini_get</span>("safe_mode") == 0<span>)
</span><span>107</span> <span> {
</span><span>108</span> @<span>set_time_limit</span>(300<span>);
</span><span>109</span> <span> }
</span><span>110</span>
<span>111</span> <span>/*</span>
<span>112</span> <span> * ------------------------------------------------------
</span><span>113</span> <span> * Start the timer... tick tock tick tock...
</span><span>114</span> <span> * ------------------------------------------------------
</span><span>115</span> <span>*/</span>
<span>116</span> <span>$BM</span> =& load_class('Benchmark', 'core'<span>);
</span><span>117</span> <span>$BM</span>->mark('total_execution_time_start'<span>);
</span><span>118</span> <span>$BM</span>->mark('loading_time:_base_classes_start'<span>);
</span><span>119</span>
<span>120</span> <span>/*</span>
<span>121</span> <span> * ------------------------------------------------------
</span><span>122</span> <span> * Instantiate the hooks class
</span><span>123</span> <span> * ------------------------------------------------------
</span><span>124</span> <span>*/</span>
<span>125</span> <span>$EXT</span> =& load_class('Hooks', 'core'<span>);
</span><span>126</span>
<span>127</span> <span>/*</span>
<span>128</span> <span> * ------------------------------------------------------
</span><span>129</span> <span> * Is there a "pre_system" hook?
</span><span>130</span> <span> * ------------------------------------------------------
</span><span>131</span> <span>*/</span>
<span>132</span> <span>$EXT</span>->_call_hook('pre_system'<span>);
</span><span>133</span>
<span>134</span> <span>/*</span>
<span>135</span> <span> * ------------------------------------------------------
</span><span>136</span> <span> * Instantiate the config class
</span><span>137</span> <span> * ------------------------------------------------------
</span><span>138</span> <span>*/</span>
<span>139</span> <span>$CFG</span> =& load_class('Config', 'core'<span>);
</span><span>140</span>
<span>141</span> <span>//</span><span> Do we have any manually set config items in the index.php file?</span>
<span>142</span> <span>if</span> (<span>isset</span>(<span>$assign_to_config</span><span>))
</span><span>143</span> <span> {
</span><span>144</span> <span>$CFG</span>->_assign_to_config(<span>$assign_to_config</span><span>);
</span><span>145</span> <span> }
</span><span>146</span>
<span>147</span> <span>/*</span>
<span>148</span> <span> * ------------------------------------------------------
</span><span>149</span> <span> * Instantiate the UTF-8 class
</span><span>150</span> <span> * ------------------------------------------------------
</span><span>151</span> <span> *
</span><span>152</span> <span> * Note: Order here is rather important as the UTF-8
</span><span>153</span> <span> * class needs to be used very early on, but it cannot
</span><span>154</span> <span> * properly determine if UTf-8 can be supported until
</span><span>155</span> <span> * after the Config class is instantiated.
</span><span>156</span> <span> *
</span><span>157</span> <span>*/</span>
<span>158</span>
<span>159</span> <span>$UNI</span> =& load_class('Utf8', 'core'<span>);
</span><span>160</span>
<span>161</span> <span>/*</span>
<span>162</span> <span> * ------------------------------------------------------
</span><span>163</span> <span> * Instantiate the URI class
</span><span>164</span> <span> * ------------------------------------------------------
</span><span>165</span> <span>*/</span>
<span>166</span> <span>$URI</span> =& load_class('URI', 'core'<span>);
</span><span>167</span>
<span>168</span> <span>/*</span>
<span>169</span> <span> * ------------------------------------------------------
</span><span>170</span> <span> * Instantiate the routing class and set the routing
</span><span>171</span> <span> * ------------------------------------------------------
</span><span>172</span> <span>*/</span>
<span>173</span> <span>$RTR</span> =& load_class('Router', 'core'<span>);
</span><span>174</span> <span>$RTR</span>-><span>_set_routing();
</span><span>175</span>
<span>176</span> <span>//</span><span> Set any routing overrides that may exist in the main index file</span>
<span>177</span> <span>if</span> (<span>isset</span>(<span>$routing</span><span>))
</span><span>178</span> <span> {
</span><span>179</span> <span>$RTR</span>->_set_overrides(<span>$routing</span><span>);
</span><span>180</span> <span> }
</span><span>181</span>
<span>182</span> <span>/*</span>
<span>183</span> <span> * ------------------------------------------------------
</span><span>184</span> <span> * Instantiate the output class
</span><span>185</span> <span> * ------------------------------------------------------
</span><span>186</span> <span>*/</span>
<span>187</span> <span>$OUT</span> =& load_class('Output', 'core'<span>);
</span><span>188</span>
<span>189</span> <span>/*</span>
<span>190</span> <span> * ------------------------------------------------------
</span><span>191</span> <span> * Is there a valid cache file? If so, we're done...
</span><span>192</span> <span> * ------------------------------------------------------
</span><span>193</span> <span>*/</span>
<span>194</span> <span>if</span> (<span>$EXT</span>->_call_hook('cache_override') === <span>FALSE</span><span>)
</span><span>195</span> <span> {
</span><span>196</span> <span>if</span> (<span>$OUT</span>->_display_cache(<span>$CFG</span>, <span>$URI</span>) == <span>TRUE</span><span>)
</span><span>197</span> <span> {
</span><span>198</span> <span>exit</span><span>;
</span><span>199</span> <span> }
</span><span>200</span> <span> }
</span><span>201</span>
<span>202</span> <span>/*</span>
<span>203</span> <span> * -----------------------------------------------------
</span><span>204</span> <span> * Load the security class for xss and csrf support
</span><span>205</span> <span> * -----------------------------------------------------
</span><span>206</span> <span>*/</span>
<span>207</span> <span>$SEC</span> =& load_class('Security', 'core'<span>);
</span><span>208</span>
<span>209</span> <span>/*</span>
<span>210</span> <span> * ------------------------------------------------------
</span><span>211</span> <span> * Load the Input class and sanitize globals
</span><span>212</span> <span> * ------------------------------------------------------
</span><span>213</span> <span>*/</span>
<span>214</span> <span>$IN</span> =& load_class('Input', 'core'<span>);
</span><span>215</span>
<span>216</span> <span>/*</span>
<span>217</span> <span> * ------------------------------------------------------
</span><span>218</span> <span> * Load the Language class
</span><span>219</span> <span> * ------------------------------------------------------
</span><span>220</span> <span>*/</span>
<span>221</span> <span>$LANG</span> =& load_class('Lang', 'core'<span>);
</span><span>222</span>
<span>223</span> <span>/*</span>
<span>224</span> <span> * ------------------------------------------------------
</span><span>225</span> <span> * Load the app controller and local controller
</span><span>226</span> <span> * ------------------------------------------------------
</span><span>227</span> <span> *
</span><span>228</span> <span>*/</span>
<span>229</span> <span>//</span><span> Load the base controller class</span>
<span>230</span> <span>require</span> BASEPATH.'core/Controller.php'<span>;
</span><span>231</span>
<span>232</span> <span>function</span> &<span>get_instance()
</span><span>233</span> <span> {
</span><span>234</span> <span>return</span> CI_Controller::<span>get_instance();
</span><span>235</span> <span> }
</span><span>236</span>
<span>237</span>
<span>238</span> <span>if</span> (<span>file_exists</span>(APPPATH.'core/'.<span>$CFG</span>->config['subclass_prefix'].'Controller.php'<span>))
</span><span>239</span> <span> {
</span><span>240</span> <span>require</span> APPPATH.'core/'.<span>$CFG</span>->config['subclass_prefix'].'Controller.php'<span>;
</span><span>241</span> <span> }
</span><span>242</span>
<span>243</span> <span>//</span><span> Load the local application controller
</span><span>244</span> <span> // Note: The Router class automatically validates the controller path using the router->_validate_request().
</span><span>245</span> <span> // If this include fails it means that the default controller in the Routes.php file is not resolving to something valid.</span>
<span>246</span> <span>if</span> ( ! <span>file_exists</span>(APPPATH.'controllers/'.<span>$RTR</span>->fetch_directory().<span>$RTR</span>->fetch_class().'.php'<span>))
</span><span>247</span> <span> {
</span><span>248</span> show_error('Unable to load your default controller. Please make sure the controller specified in your Routes.php file is valid.'<span>);
</span><span>249</span> <span> }
</span><span>250</span>
<span>251</span> <span>include</span>(APPPATH.'controllers/'.<span>$RTR</span>->fetch_directory().<span>$RTR</span>->fetch_class().'.php'<span>);
</span><span>252</span>
<span>253</span> <span>//</span><span> Set a mark point for benchmarking</span>
<span>254</span> <span>$BM</span>->mark('loading_time:_base_classes_end'<span>);
</span><span>255</span>
<span>256</span> <span>/*</span>
<span>257</span> <span> * ------------------------------------------------------
</span><span>258</span> <span> * Security check
</span><span>259</span> <span> * ------------------------------------------------------
</span><span>260</span> <span> *
</span><span>261</span> <span> * None of the functions in the app controller or the
</span><span>262</span> <span> * loader class can be called via the URI, nor can
</span><span>263</span> <span> * controller functions that begin with an underscore
</span><span>264</span> <span>*/</span>
<span>265</span> <span>$class</span> = <span>$RTR</span>-><span>fetch_class();
</span><span>266</span> <span>$method</span> = <span>$RTR</span>-><span>fetch_method();
</span><span>267</span>
<span>268</span> <span>if</span> ( ! <span>class_exists</span>(<span>$class</span><span>)
</span><span>269</span> OR <span>strncmp</span>(<span>$method</span>, '_', 1) == 0
<span>270</span> OR <span>in_array</span>(<span>strtolower</span>(<span>$method</span>), <span>array_map</span>('strtolower', <span>get_class_methods</span>('CI_Controller'<span>)))
</span><span>271</span> <span> )
</span><span>272</span> <span> {
</span><span>273</span> <span>if</span> ( ! <span>empty</span>(<span>$RTR</span>->routes['404_override'<span>]))
</span><span>274</span> <span> {
</span><span>275</span> <span>$x</span> = <span>explode</span>('/', <span>$RTR</span>->routes['404_override'<span>]);
</span><span>276</span> <span>$class</span> = <span>$x</span>[0<span>];
</span><span>277</span> <span>$method</span> = (<span>isset</span>(<span>$x</span>[1]) ? <span>$x</span>[1] : 'index'<span>);
</span><span>278</span> <span>if</span> ( ! <span>class_exists</span>(<span>$class</span><span>))
</span><span>279</span> <span> {
</span><span>280</span> <span>if</span> ( ! <span>file_exists</span>(APPPATH.'controllers/'.<span>$class</span>.'.php'<span>))
</span><span>281</span> <span> {
</span><span>282</span> show_404("{<span>$class</span>}/{<span>$method</span>}"<span>);
</span><span>283</span> <span> }
</span><span>284</span>
<span>285</span> <span>include_once</span>(APPPATH.'controllers/'.<span>$class</span>.'.php'<span>);
</span><span>286</span> <span> }
</span><span>287</span> <span> }
</span><span>288</span> <span>else</span>
<span>289</span> <span> {
</span><span>290</span> show_404("{<span>$class</span>}/{<span>$method</span>}"<span>);
</span><span>291</span> <span> }
</span><span>292</span> <span> }
</span><span>293</span>
<span>294</span> <span>/*</span>
<span>295</span> <span> * ------------------------------------------------------
</span><span>296</span> <span> * Is there a "pre_controller" hook?
</span><span>297</span> <span> * ------------------------------------------------------
</span><span>298</span> <span>*/</span>
<span>299</span> <span>$EXT</span>->_call_hook('pre_controller'<span>);
</span><span>300</span>
<span>301</span> <span>/*</span>
<span>302</span> <span> * ------------------------------------------------------
</span><span>303</span> <span> * Instantiate the requested controller
</span><span>304</span> <span> * ------------------------------------------------------
</span><span>305</span> <span>*/</span>
<span>306</span> <span>//</span><span> Mark a start point so we can benchmark the controller</span>
<span>307</span> <span>$BM</span>->mark('controller_execution_time_( '.<span>$class</span>.' / '.<span>$method</span>.' )_start'<span>);
</span><span>308</span>
<span>309</span> <span>$CI</span> = <span>new</span> <span>$class</span><span>();
</span><span>310</span>
<span>311</span> <span>/*</span>
<span>312</span> <span> * ------------------------------------------------------
</span><span>313</span> <span> * Is there a "post_controller_constructor" hook?
</span><span>314</span> <span> * ------------------------------------------------------
</span><span>315</span> <span>*/</span>
<span>316</span> <span>$EXT</span>->_call_hook('post_controller_constructor'<span>);
</span><span>317</span>
<span>318</span> <span>/*</span>
<span>319</span> <span> * ------------------------------------------------------
</span><span>320</span> <span> * Call the requested method
</span><span>321</span> <span> * ------------------------------------------------------
</span><span>322</span> <span>*/</span>
<span>323</span> <span>//</span><span> Is there a "remap" function? If so, we call it instead</span>
<span>324</span> <span>if</span> (<span>method_exists</span>(<span>$CI</span>, '_remap'<span>))
</span><span>325</span> <span> {
</span><span>326</span> <span>$CI</span>->_remap(<span>$method</span>, <span>array_slice</span>(<span>$URI</span>->rsegments, 2<span>));
</span><span>327</span> <span> }
</span><span>328</span> <span>else</span>
<span>329</span> <span> {
</span><span>330</span> <span>//</span><span> is_callable() returns TRUE on some versions of PHP 5 for private and protected
</span><span>331</span> <span> // methods, so we'll use this workaround for consistent behavior</span>
<span>332</span> <span>if</span> ( ! <span>in_array</span>(<span>strtolower</span>(<span>$method</span>), <span>array_map</span>('strtolower', <span>get_class_methods</span>(<span>$CI</span><span>))))
</span><span>333</span> <span> {
</span><span>334</span> <span>//</span><span> Check and see if we are using a 404 override and use it.</span>
<span>335</span> <span>if</span> ( ! <span>empty</span>(<span>$RTR</span>->routes['404_override'<span>]))
</span><span>336</span> <span> {
</span><span>337</span> <span>$x</span> = <span>explode</span>('/', <span>$RTR</span>->routes['404_override'<span>]);
</span><span>338</span> <span>$class</span> = <span>$x</span>[0<span>];
</span><span>339</span> <span>$method</span> = (<span>isset</span>(<span>$x</span>[1]) ? <span>$x</span>[1] : 'index'<span>);
</span><span>340</span> <span>if</span> ( ! <span>class_exists</span>(<span>$class</span><span>))
</span><span>341</span> <span> {
</span><span>342</span> <span>if</span> ( ! <span>file_exists</span>(APPPATH.'controllers/'.<span>$class</span>.'.php'<span>))
</span><span>343</span> <span> {
</span><span>344</span> show_404("{<span>$class</span>}/{<span>$method</span>}"<span>);
</span><span>345</span> <span> }
</span><span>346</span>
<span>347</span> <span>include_once</span>(APPPATH.'controllers/'.<span>$class</span>.'.php'<span>);
</span><span>348</span> <span>unset</span>(<span>$CI</span><span>);
</span><span>349</span> <span>$CI</span> = <span>new</span> <span>$class</span><span>();
</span><span>350</span> <span> }
</span><span>351</span> <span> }
</span><span>352</span> <span>else</span>
<span>353</span> <span> {
</span><span>354</span> show_404("{<span>$class</span>}/{<span>$method</span>}"<span>);
</span><span>355</span> <span> }
</span><span>356</span> <span> }
</span><span>357</span>
<span>358</span> <span>//</span><span> Call the requested method.
</span><span>359</span> <span> // Any URI segments present (besides the class/function) will be passed to the method for convenience</span>
<span>360</span> <span>call_user_func_array</span>(<span>array</span>(&<span>$CI</span>, <span>$method</span>), <span>array_slice</span>(<span>$URI</span>->rsegments, 2<span>));
</span><span>361</span> <span> }
</span><span>362</span>
<span>363</span>
<span>364</span> <span>//</span><span> Mark a benchmark end point</span>
<span>365</span> <span>$BM</span>->mark('controller_execution_time_( '.<span>$class</span>.' / '.<span>$method</span>.' )_end'<span>);
</span><span>366</span>
<span>367</span> <span>/*</span>
<span>368</span> <span> * ------------------------------------------------------
</span><span>369</span> <span> * Is there a "post_controller" hook?
</span><span>370</span> <span> * ------------------------------------------------------
</span><span>371</span> <span>*/</span>
<span>372</span> <span>$EXT</span>->_call_hook('post_controller'<span>);
</span><span>373</span>
<span>374</span> <span>/*</span>
<span>375</span> <span> * ------------------------------------------------------
</span><span>376</span> <span> * Send the final rendered output to the browser
</span><span>377</span> <span> * ------------------------------------------------------
</span><span>378</span> <span>*/</span>
<span>379</span> <span>if</span> (<span>$EXT</span>->_call_hook('display_override') === <span>FALSE</span><span>)
</span><span>380</span> <span> {
</span><span>381</span> <span>$OUT</span>-><span>_display();
</span><span>382</span> <span> }
</span><span>383</span>
<span>384</span> <span>/*</span>
<span>385</span> <span> * ------------------------------------------------------
</span><span>386</span> <span> * Is there a "post_system" hook?
</span><span>387</span> <span> * ------------------------------------------------------
</span><span>388</span> <span>*/</span>
<span>389</span> <span>$EXT</span>->_call_hook('post_system'<span>);
</span><span>390</span>
<span>391</span> <span>/*</span>
<span>392</span> <span> * ------------------------------------------------------
</span><span>393</span> <span> * Close the DB connection if one exists
</span><span>394</span> <span> * ------------------------------------------------------
</span><span>395</span> <span>*/</span>
<span>396</span> <span>if</span> (<span>class_exists</span>('CI_DB') AND <span>isset</span>(<span>$CI</span>-><span>db))
</span><span>397</span> <span> {
</span><span>398</span> <span>$CI</span>->db-><span>close();
</span><span>399</span> <span> }
</span><span>400</span>
<span>401</span>
<span>402</span> <span>/*</span><span> End of file CodeIgniter.php </span><span>*/</span>
<span>403</span> <span>/*</span><span> Location: ./system/core/CodeIgniter.php </span><span>*/</span>在CodeIgniter中，可以看到开头的英文描述，该脚本时系统初始化文件，主要作用是装载基类和执行请求。
31-45行：定义了CI_VERSION常量，描述当前框架版本，CI_CORE常量，目前我也不清楚没探究过，注释是CI的分支，啥意思？
52行：加载系统核心目录下的Common.php文件，Load the global functions，记得前一篇中说到，一般一个项目会将很多公共方法放在一个脚本中加载进来，通常取名Utilities.php，也可是Common.php，这里的Common.php也是这个意思，如它的解释是“加载全局函数”，即这里的函数都是后边直接拿来用的。在这个脚本中有两个重要的方法（目前来说）一个是get_config，单独拿出来如下
<span> 1</span> <?<span>php
</span><span> 2</span> <span>/*</span><span>*
</span><span> 3</span> <span>* Loads the main config.php file
</span><span> 4</span> <span>*
</span><span> 5</span> <span>* This function lets us grab the config file even if the Config class
</span><span> 6</span> <span>* hasn't been instantiated yet
</span><span> 7</span> <span>*
</span><span> 8</span> <span>* @access private
</span><span> 9</span> <span>* @return array
</span><span>10</span> <span>*/</span>
<span>11</span> <span>if</span> ( ! <span>function_exists</span>('get_config'<span>))
</span><span>12</span> <span>{
</span><span>13</span> <span>function</span> &get_config(<span>$replace</span> = <span>array</span><span>())
</span><span>14</span> <span> {
</span><span>15</span> <span>static</span> <span>$_config</span><span>;
</span><span>16</span>
<span>17</span> <span>if</span> (<span>isset</span>(<span>$_config</span><span>))
</span><span>18</span> <span> {
</span><span>19</span> <span>return</span> <span>$_config</span>[0<span>];
</span><span>20</span> <span> }
</span><span>21</span>
<span>22</span> <span>//</span><span> Is the config file in the environment folder?</span>
<span>23</span> <span>if</span> ( ! <span>defined</span>('ENVIRONMENT') OR ! <span>file_exists</span>(<span>$file_path</span> = APPPATH.'config/'.ENVIRONMENT.'/config.php'<span>))
</span><span>24</span> <span> {
</span><span>25</span> <span>$file_path</span> = APPPATH.'config/config.php'<span>;
</span><span>26</span> <span> }
</span><span>27</span>
<span>28</span> <span>//</span><span> Fetch the config file</span>
<span>29</span> <span>if</span> ( ! <span>file_exists</span>(<span>$file_path</span><span>))
</span><span>30</span> <span> {
</span><span>31</span> <span>exit</span>('The configuration file does not exist.'<span>);
</span><span>32</span> <span> }
</span><span>33</span>
<span>34</span> <span>require</span>(<span>$file_path</span><span>);
</span><span>35</span>
<span>36</span> <span>//</span><span> Does the $config array exist in the file?</span>
<span>37</span> <span>if</span> ( ! <span>isset</span>(<span>$config</span>) OR ! <span>is_array</span>(<span>$config</span><span>))
</span><span>38</span> <span> {
</span><span>39</span> <span>exit</span>('Your config file does not appear to be formatted correctly.'<span>);
</span><span>40</span> <span> }
</span><span>41</span>
<span>42</span> <span>//</span><span> Are any values being dynamically replaced?</span>
<span>43</span> <span>if</span> (<span>count</span>(<span>$replace</span>) > 0<span>)
</span><span>44</span> <span> {
</span><span>45</span> <span>foreach</span> (<span>$replace</span> <span>as</span> <span>$key</span> => <span>$val</span><span>)
</span><span>46</span> <span> {
</span><span>47</span> <span>if</span> (<span>isset</span>(<span>$config</span>[<span>$key</span><span>]))
</span><span>48</span> <span> {
</span><span>49</span> <span>$config</span>[<span>$key</span>] = <span>$val</span><span>;
</span><span>50</span> <span> }
</span><span>51</span> <span> }
</span><span>52</span> <span> }
</span><span>53</span>
<span>54</span> <span>$_config</span>[0] =& <span>$config</span><span>;
</span><span>55</span> <span>return</span> <span>$_config</span>[0<span>];
</span><span>56</span> <span> }
</span><span>57</span> }注释说它加载主要的config.php文件，它使得我们能抓取到配置文件，即便配置类还未被实例化。在CI中，有专门的核心配置类CI_Config来加载配置信息，而这里的get_config方法也能获得主要配置信息，注意是主要配置信息，在application/config目录下有很多其他的配置信息文件（前面在自定义配置变量时也说过CI将配置信息分为了很多文件），其中有一个config.php文件就是get_config能获取到的，这个文件存放的就是基本信息，如果你还想获取其他的配置信息，貌似就要用配置类了。所以如果想添加节本配置信息就在这个里边。
如果是第一次调用get_config方法，先声明静态变量$_config，如果已定义则直接返回它的索引为0的子数组。然后查看APPPATH/config/ENVIRONMENT/config.php文件是否存在（前面打印已知ENVIRONMENT常量值，未改动就是development，原始的框架中没有这个目录，所以这里加载的是application/config/config.php（只加载了这一个，其他的配置文件没有），可以打开看看config.php中定义了一个$config数组，一些基本定义如基础链接、链接后缀、编码、语言、缓存、日志、钩子等等。如果传入一个关联数组，它会将键-值（临时）加入$_config中。总之，get_config方法主要得到的是config.php中定义的数组变量。
与get_config相关的config_item方法则是得到这个数组变量中的某一项。
另一个比较重要的方法是load_class：
<span> 1</span> <?<span>php
</span><span> 2</span> <span>/*</span><span>*
</span><span> 3</span> <span>* Class registry
</span><span> 4</span> <span>*
</span><span> 5</span> <span>* This function acts as a singleton. If the requested class does not
</span><span> 6</span> <span>* exist it is instantiated and set to a static variable. If it has
</span><span> 7</span> <span>* previously been instantiated the variable is returned.
</span><span> 8</span> <span>*
</span><span> 9</span> <span>* @access public
</span><span>10</span> <span>* @param string the class name being requested
</span><span>11</span> <span>* @param string the directory where the class should be found
</span><span>12</span> <span>* @param string the class name prefix
</span><span>13</span> <span>* @return object
</span><span>14</span> <span>*/</span>
<span>15</span> <span>if</span> ( ! <span>function_exists</span>('load_class'<span>))
</span><span>16</span> <span>{
</span><span>17</span> <span>function</span> &load_class(<span>$class</span>, <span>$directory</span> = 'libraries', <span>$prefix</span> = 'CI_'<span>)
</span><span>18</span> <span> {
</span><span>19</span> <span>static</span> <span>$_classes</span> = <span>array</span><span>();
</span><span>20</span>
<span>21</span> <span>//</span><span> Does the class exist? If so, we're done...</span>
<span>22</span> <span>if</span> (<span>isset</span>(<span>$_classes</span>[<span>$class</span><span>]))
</span><span>23</span> <span> {
</span><span>24</span> <span>return</span> <span>$_classes</span>[<span>$class</span><span>];
</span><span>25</span> <span> }
</span><span>26</span>
<span>27</span> <span>$name</span> = <span>FALSE</span><span>;
</span><span>28</span>
<span>29</span> <span>//</span><span> Look for the class first in the local application/libraries folder
</span><span>30</span> <span> // then in the native system/libraries folder</span>
<span>31</span> <span>foreach</span> (<span>array</span>(APPPATH, BASEPATH) <span>as</span> <span>$path</span><span>)
</span><span>32</span> <span> {
</span><span>33</span> <span>if</span> (<span>file_exists</span>(<span>$path</span>.<span>$directory</span>.'/'.<span>$class</span>.'.php'<span>))
</span><span>34</span> <span> {
</span><span>35</span> <span>$name</span> = <span>$prefix</span>.<span>$class</span><span>;
</span><span>36</span>
<span>37</span> <span>if</span> (<span>class_exists</span>(<span>$name</span>) === <span>FALSE</span><span>)
</span><span>38</span> <span> {
</span><span>39</span> <span>require</span>(<span>$path</span>.<span>$directory</span>.'/'.<span>$class</span>.'.php'<span>);
</span><span>40</span> <span> }
</span><span>41</span>
<span>42</span> <span>break</span><span>;
</span><span>43</span> <span> }
</span><span>44</span> <span> }
</span><span>45</span>
<span>46</span> <span>//</span><span> Is the request a class extension? If so we load it too</span>
<span>47</span> <span>if</span> (<span>file_exists</span>(APPPATH.<span>$directory</span>.'/'.config_item('subclass_prefix').<span>$class</span>.'.php'<span>))
</span><span>48</span> <span> {
</span><span>49</span> <span>$name</span> = config_item('subclass_prefix').<span>$class</span><span>;
</span><span>50</span>
<span>51</span> <span>if</span> (<span>class_exists</span>(<span>$name</span>) === <span>FALSE</span><span>)
</span><span>52</span> <span> {
</span><span>53</span> <span>require</span>(APPPATH.<span>$directory</span>.'/'.config_item('subclass_prefix').<span>$class</span>.'.php'<span>);
</span><span>54</span> <span> }
</span><span>55</span> <span> }
</span><span>56</span>
<span>57</span> <span>//</span><span> Did we find the class?</span>
<span>58</span> <span>if</span> (<span>$name</span> === <span>FALSE</span><span>)
</span><span>59</span> <span> {
</span><span>60</span> <span>//</span><span> Note: We use exit() rather then show_error() in order to avoid a
</span><span>61</span> <span> // self-referencing loop with the Excptions class</span>
<span>62</span> <span>exit</span>('Unable to locate the specified class: '.<span>$class</span>.'.php'<span>);
</span><span>63</span> <span> }
</span><span>64</span>
<span>65</span> <span>//</span><span> Keep track of what we just loaded</span>
<span>66</span> is_loaded(<span>$class</span><span>);
</span><span>67</span>
<span>68</span> <span>$_classes</span>[<span>$class</span>] = <span>new</span> <span>$name</span><span>();
</span><span>69</span> <span>return</span> <span>$_classes</span>[<span>$class</span><span>];
</span><span>70</span> <span> }
</span><span>71</span> }先看它的注释：这个方法作为一个单例，如果被请求的类没有出现过，则该类会被实例化为一个static variable，如果先前被实例化过则直接返回它。它的三个参数分别是请求的类名、所在目录，类名前缀。可以看到，目录默认是libraries，在application和system中均有它，它就是存放我们自定义的类库或者CI自带的类库的地方，就是自定义工具和CI提供的工具，如日历类、加密类、Ftp类、日志类、Session会话类、Email邮件收发类、JavaScript类、ZIP压缩类等等。或许你已经注意到这里返回的是引用而非值，就像它将加载的类作为静态变量一样，这些细节地方最终提高了整个系统的访问速度。
大致流程：先定義一個靜態數組，若數組中已有該類別直接回傳。先後掃描APPPATH和BASEPATH（前面已知這兩個常數值）資料夾下的$directory（預設值是libraries）目錄下的$class.php檔案是否存在，存在則加上CI的標準類別前綴CI_（第三個參數的預設值），在檢查類別存在與否，存在則require該檔案（從這裡可知，class_exists()在判斷類別是否存在時並不需要先載入該類別檔案），一旦檔案出現則載入它，並break跳出。注意掃描順序，先APPPATH後BASEPATH，假如只傳第一個參數類名，則優先在我們自己開發的application目錄libraries中尋找，然後才去system目錄的libraries下邊。
由於我們可以將CI的核心類別擴展（繼承它們），所以在掃描APPPATH和BASEPATH的核心類別（名稱以CI_為前綴）目錄後，還要掃描APPPATH的libraries下邊是否有自訂的擴充類別（預設以MY_為前綴），有的話也要載入它們，然後實例化一個對應物件（有擴充類別是擴充類別）存入$_classes靜態陣列並傳回該物件。
對Common.php有大致了解後回到CodeIgniter.php腳本。
54-66行：載入APPPATH.'config/constants.php'腳本，constants.php如同名字一樣放的是framework constants，集中定義了一些常數，所以我們在加入常數時就可以放到這裡邊來定義。
68-78行：首先定義了一個自訂錯誤處理方法_exception_handler。判斷php版本，非5.3關閉magic_quotes引用，這個配置在5.3版本已棄用，提高安全性。
80-99行：這裡就是將前面說過的$assign_to_config自訂設定資訊數組暫時加到$_config數組中，透過get_config方法實現，前面說過$assign_to_config預設是沒有定義的，這裡的if語句也不會運行。
101-109行：設定自訂腳本最大執行時間為300秒（略長，跑日誌的話得更長）
111-118行：載入核心類別Benchmark，設定兩個標記點。 Benchmark基準測試類，就是測試某個開始標記到結束標記之間佔用的內存大小、執行時間等信息，測試嘛，當然它要結合CI中一個叫分析器的東西使用。
120-132行：載入核心類別Hooks，鉤子，設定了一個系統開始執行的鉤子（實際上未執行，因為application/config/config.php關於它的設定資訊預設為false，即不啟用鉤子）。它就相當於一個觸發器，在某個東西要執行前開始執行某些程式碼，例如控制器載入前、載入後等，一旦控制器載入就執行指定的程式碼。在這裡，它嘗試呼叫一個pre_system（系統執行前）的擴展，預設不執行。
134-145行：加載核心類Config，配置類，它用來加載其他需需要的配置信息，並且它再次加載$assign_to_config數組中配置信息如果該數組定義了的話。
147-159行：載入核心類別Utf8，編碼類別。
161-166行：載入核心類別URI，路由。
168-180行：載入核心類Router，路徑處理類，_set_routing方法設定好存取路徑。如果路徑配置數組$routing（前面提到預設是註解掉的）定義了的話，將覆蓋預設的路由配置。如果你輸入了不存在的腳本路徑，在這一步就停住，開始報404了，當然還得Router裡邊的方法處理。
Router類別裡面，URI作為它的一個成員存在，實際處理方法在URI類中，熟悉點的都知道CI的訪問方式默認是段（segment）的形式，據說更有利於搜尋引擎。一個簡單的存取方式是這樣的localhost/ci/index.php/Controller/Function/Arguments，它們將訪問的形式解析為需要的控制器，調用的方法，以及提供的參數列表，當然也可啟用傳統的查詢字串形式。具體方法略複雜。
187行：載入核心類別Output。
189-200行：透過Hooks類別和Output類別偵測有無緩存，有的話直接輸出快取頁面，跳出腳本了。這也是在CI的介紹中應用程式流程圖部分，當路徑處理完後，若有快取直接輸出的原因。
207行：載入核心類別Security。
214行：載入核心類別Input。
221行：載入核心類別Lang，語言處理。
229-235行：載入核心類別Controller，它是所有控制器的基類，而get_instance全域方法也能得到它的實例，Controller的牛逼之處在於，它將前面所有透過load_calss載入的libraries（預設）目錄（APPPATH和BASEPATH）中的工具庫全部實例化為對象，並作為它的屬性成員。所以這裡的get_instance方法得到的實例也被CI稱為超物件（好像是這個名字），因為透過這個物件就可以取得所有透過前面載入的物件實例。
238-242行：載入自訂的，對上一步的核心類別CI_Controller的擴充類別的文件，預設就是MY_Controller，當然前提是如果你擴充了的的話。
243-251行：透過核心類別Router的實例，擷取目前存取的控制器所在的目錄和類別名，不存在則報錯，存在則載入它，這裡就載入了預設的welcome控制器檔案。當然如果你自己定義了控制器類別檔案並訪問，也是在這裡被include進來的（透過Router類別提取子目錄$RTR->fetch_directory()，若存在，提取類別名稱$RTR->fetch_class()來找），大概在246行的if語句塊，就是檢查這個類別檔案是否存在。
252行：設定一個基準測試結束標記，標記載入基本核心類別結束（這些測試預設不會執行）。
256-292行：安全檢查。先透過Router類別取得類別名稱和要執行的方法名，if條件檢查3項內容。 1. 上面的243-251行是找到了控制器對應的腳本，並且加載了它，但是假如這只是一個名字匹配的空腳本呢？裡邊什麼都沒寫就不行了，於是要檢查類別的定義是否存在（class_exists），2. 以下劃線_開頭的方法名稱不能執行，直接報錯，當然這是CI自己的規則，也就是說無論你的類別定義的以_開頭的方法即使是公有存取屬性也不行（除了一個_remap），3. 當類別中的方法根控制器核心類別中的方法同名時也不行。定義方法名時有個印象就行了。進入if中就很可能會404了。
298行：Hooks類別嘗試呼叫一個pre_controller（控制器執行前）的擴展，預設沒有。
301-309行：基準測試類設定一個起點標記，目的在於測試控制器執行的時長（預設不顯示測試資訊），並且實例化前面載入的控制器類，預設的就是Welcome。
315行：Hooks嘗試執行post_controller_constructor（所呼叫的控制器類別建構完成後）的擴展，預設沒有。
317-364行：開始呼叫指定的控制器類別的指定方法（當然這裡是預設控制器Welcome的預設方法index）。看看這個流程，首先一個if判斷，如果你的控制器類別中有方法_remap，只呼叫它了，所以前面說以下劃線開頭的方法除了_remap，這也是CI的一個類別的方法的規則，有了這個重映射方法，只調它。預設的Welcome
