配置系统常量
1、当文件系统工作的时候检查并配置这些首选项
文件系统运行的时候这些默认的值会适当的增加系统的安全性，但是在php或apache的底层单独的为每各用户开一个进程的时候，使用八进制的值永远是正确的
FILE_READ_MODE 读取文件的模式
FILE_WRITE_MODE   写入文件的模式
DIR_READ_MODE   读取目录的模式
DIR_WRITE_MODE 写入目录的模式

 
2、文件流模式
当我们使用fopen()/popen()的时候需要这些模式
define('FOPEN_READ', 'rb');
define('FOPEN_READ_WRITE', 'r+b');
define('FOPEN_WRITE_CREATE_DESTRUCTIVE', 'wb');
define('FOPEN_READ_WRITE_CREATE_DESTRUCTIVE',  'w+b');
define('FOPEN_WRITE_CREATE', 'ab');
define('FOPEN_READ_WRITE_CREATE', 'a+b');
define('FOPEN_WRITE_CREATE_STRICT', 'xb');
define('FOPEN_READ_WRITE_CREATE_STRICT',  'x+b');

文件源码：
复制代码 代码如下:
[php] 
<?php  if ( ! defined('BASEPATH')) exit('No direct script access allowed'); 

/*
|--------------------------------------------------------------------------
| File and Directory Modes
|--------------------------------------------------------------------------

| These prefs 控制台、首选项 are used when checking and setting modes when working
| with the file system.  The defaults are fine 罚款 on servers with proper
| security, but you may wish (or even need) to change the values in
| certain environments (Apache running a separate process for each
| user, PHP under CGI with Apache suEXEC, etc.).  Octal values should
| always be used to set the mode correctly.

*/ 
define('FILE_READ_MODE', 0644); 
define('FILE_WRITE_MODE', 0666); 
define('DIR_READ_MODE', 0755); 
define('DIR_WRITE_MODE', 0777); 

/*
|--------------------------------------------------------------------------
| File Stream Modes 文件流模式
|--------------------------------------------------------------------------

| These modes are used when working with fopen()/popen()

*/ 

define('FOPEN_READ',                            'rb'); 
define('FOPEN_READ_WRITE',                      'r+b'); 
define('FOPEN_WRITE_CREATE_DESTRUCTIVE',        'wb'); // truncates existing file data, use with care 
define('FOPEN_READ_WRITE_CREATE_DESTRUCTIVE',   'w+b'); // truncates existing file data, use with care 
define('FOPEN_WRITE_CREATE',                    'ab'); 
define('FOPEN_READ_WRITE_CREATE',               'a+b'); 
define('FOPEN_WRITE_CREATE_STRICT',             'xb'); 
define('FOPEN_READ_WRITE_CREATE_STRICT',        'x+b'); 

 
/* End of file constants.php */ 
/* Location: ./application/config/constants.php */