Table of Contents
PHP之autoload运行机制实例分析,autoload实例分析
php中__autoload()加载问题
急,各位高人解释一下PHP中的__autoload函数以及spl_autoload_register()函数,我到网上找资料都没看懂
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PHP之autoload运行机制实例分析,autoload实例分析

Jun 13, 2016 am 09:26 AM
autoload php spl

PHP之autoload运行机制实例分析,autoload实例分析

本文较为深入的分析了PHP的autoload运行机制。对于深入理解PHP运行原理有一定的帮助作用。具体分析如下:

php实现autoload有两种方法:

1、拦截器__autoload()

2、设置全局变量函数指针autoload_func为指定函数。通常在c扩展中使用

本质上前者还是通过后者实现的。

分析过程,PHP5.3.6源码:

=>Zend/zend_vm_def.h  1894行
ZEND_VM_HANDLER(109,ZEND_FETCH_CLASS,...
=>zend_execute_API.c 1526行
zend_class_entry *zend_fetch_class(const char *class_name,...
=>zend_execute_API.c 1564行
if(zend_lookup_class_ex(class_name,class_name_len,...
=>zend_execute_API.c 1039行
ZEND_API int zend_lookup_class_ex(const char *na...
=>zend_execute_API.c 1121行
retval = zend_call_function(&fcall_info, &fcall_cache TSRMLS_CC);
=>zend_execute_API.c 758行
       zend_call_function

顾名思义,zend_call_function的主要功能是调用PHP函数。其参数fcall_info, fcall_cache,分别指向两个重要的结构,zend_fcall_info和zend_fcall_info_cache

zend_call_function主要工作流程如下:

如果fcall_cache.function_handler不为NULL,则直接执行 fcall_cache.function_handler指向的函数。
如果 fcall_cache.function_handler为NULL,则尝试查找函数名为fcall_info.function_name的函 数,如果存在的话,则执行之;
 
现总结如下,autoload机制的主要执行过程为:

(1) 检查执行器全局变量函数指针autoload_func是否为NULL。
(2) 如果autoload_func不为NULL,则直接执行autoload_func指针指向的函数用来加载类,并不检查__autoload()函数是否定义。
(3) 如果autoload_func为NULL,则查找系统中是否定义有__autoload()函数。如果没有定义,则报告错误并退出;如果定义了__autoload()函数,则执行__autoload()尝试加载类,并返回加载结果。

自动加载方便了面向对象和代码复用,但是多个类库不同的__autoload又会导致混乱。可以用spl_autoload解决,将不同开发者的拦截器函数都注册到自动加载函数的hashtable中。spl实现自动加载的机制是维护一个hashtable,里面存储有具有自动加载功能的各个函数。

当触发自动加载机制时,zend会在遍历执行这个hashtable里面的函数,直到成功加载类或加载失败后返回。
当需要使用自动加载功能时,使用函数spl_autoload_register()或spl_autoload_register('autoloadfuncitonname')
无参的spl_autoload_register()会默认加载spl_autoload()函数,该函数功能有限,只能在inlcude_path中搜索指定扩展名的类库。

有参的spl_autoload_register()默认不再加载spl_autoload()函数。
可以通过spl_autoload_functions()查看当前自动加载hashtable中的函数,该函数返回一个数组

注意:使用spl_autoload时,系统会忽略拦截器__autoload,除非显式地使用spl_autoload_register('__autoload')将其加入hashtable

希望本文所述对大家的PHP程序设计有所帮助

php中__autoload()加载问题

给你分享个我在用的吧
//自动挂载类function AutoLoad($classname){ // class类 $filepath = BASE_CLASS . $classname . '.class.php'; if (file_exists($filepath)) { return include $filepath; } //lib库文件 $filepath = BASE_LIB . $classname . '.lib.php'; if (file_exists($filepath)) { return include $filepath; }}spl_autoload_register('AutoLoad');用法:
//检查登录User::is_loginin();//自动实例化User,并执行is_loginin
 

急,各位高人解释一下PHP中的__autoload函数以及spl_autoload_register()函数,我到网上找资料都没看懂

__autoload 常用在自动加载类库处理
也就是网上说的 这种方法,根据类名,找出类文件,然后require_one
spl_autoload_register()

__autoload的最大缺陷是无法有多个autoload方法

好了, 想下下面的这个情景,你的项目引用了别人的一个项目,你的项目中有一个__autoload,别人的项目也有一个__autoload,这样两个__autoload就冲突了。解决的办法就是修改__autoload成为一个,这无疑是非常繁琐的。

因此我们急需使用一个autoload调用堆栈,这样spl的autoload系列函数就出现了。你可以使用spl_autoload_register注册多个自定义的autoload函数

如果你的PHP版本大于5.1的话,你就可以使用spl_autoload
 

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