php automatic loading method-PHP Tutorial-php.cn

The content of this article is about the automatic loading method of php. Now I share it with you. Friends in need can refer to the content of this article.

php loading File method:
1, include, include_once, requice, requice_one regular loading
2, __autoload()

3. spl_autoload_register()

##Conventional loading methodAssume we have a class file A.php, It defines a class named A:


        
         Copy after login

Then we have an index.php that needs to use this class A. The conventional writing method is


        
         Copy after login

But there is a problem, if our index.php needs to contain not only class A, but many classes, in this way, many lines of require must be written Statements can sometimes make people feel uncomfortable.

__autoload() automatically loads
But in versions after php5, we no longer need to do this.In php5, the __autoload function is automatically called when trying to use a class that has not been defined, so we can write the __autoload function to let php automatically load the class without having to write a long list of include files.

For example, in the above example, index.php can be written like this:


        
         Copy after login

Of course the above is just the simplest demonstration, __autoload just goes include_path finds class files and loads them. We can define __autoload rules for loading classes according to our own needs. Note: Since __autoload() is a function, it can only exist once.

spl_autoload_register()自动加载
但现在问题来了，如果在一个系统的实现中，如果需要使用很多其它的类库，这些类库可能是由不同的开发人员编写的，其类名与实际的磁盘文件的映射规则不尽相同。这时如果要实现类库文件的自动加载，就必须在__autoload()函数中将所有的映射规则全部实现，这样的话__autoload()函数有可能会非常复杂，甚至无法实现。最后可能会导致__autoload()函数十分臃肿，这时即便能够实现，也会给将来的维护和系统效率带来很大的负面影响。在这种情况下，难道就没有更简单清晰的解决办法了吧？答案当然是：NO!

spl_autoload_register() 满足了此类需求。它实际上创建了 autoload 函数的队列，按定义时的顺序逐个执行。相比之下， __autoload() 只可以定义一次。

bool spl_autoload_register ([ callable $autoload_function [, bool $throw = true [, bool $prepend = false ]]] )
我们继续改写上面那个例子：