When using the ThinkPHP framework, viewing its source code is useful for the two functions __autoload and apl_autoload_register, and these two functions are used for automatic loading. Its main function is that when your source code file uses a file that has not been loaded, these two functions will be triggered to load the unloaded file.
php's __autoload function is a magic function. Before this function appeared, if 100 objects were referenced in a PHP file, then the file would need to use include or require to introduce 100 class files, which would cause the PHP file to be extremely large. So there is this __autoload function.
When is the __autoload function called?
When the new keyword is used in the PHP file to instantiate an object, if the class is not defined in the PHP file, the __autoload function will be triggered. At this time, the definition of the class can be introduced. php file, and then it can be instantiated successfully. (Note: If the object that needs to be instantiated has been found in this file and the definition of the class has been found, the __autoload function will not be triggered)
#Animal.php<?php class Animal{}?>
#main.php<?php function __autoload($classname){ $classpath = "{$classname}.php"; if(file_exists($classpath)){ require_once($classpath); }else{ echo $classpath." not be found!"; } } $ani = new Animal();?>
Like the above two files, run php main.php
(1) When running to new Animal(), it is found that class Animal is not defined;
(2) The __autoload function is triggered, which introduces the Animal.php file;
(3) The instantiation is successful.
Okay, after understanding the role of the __autoload function, let’s take a look at the role of the spl_autoload_register function.
The role of the spl_autoload_register function is to replace the custom function settings with the __autoload function (note: when __autoload and spl_autoload_register appear in the file at the same time, spl_autoload_register shall prevail)
Then changing main.php to the following will have the same effect Function:
#main.php<?php function myLoad($classname){ $classpath = "{$classname}.php"; if(file_exists($classpath)){ require_once($classpath); }else{ echo $classpath." not be found!"; } } spl_autoload_register("myLoad"); $ani = new Animal();?>
When using the ThinkPHP framework, it is useful to check its source code to use the two functions __autoload and apl_autoload_register, and these two functions are used for automatic loading. Data source https://blog.csdn.net/gavin_new/article/details/52805811
Its main function is that when your source code file uses a file that has not been loaded, these two functions will be triggered to load it. This unloaded file
php's __autoload function is a magic function. Before this function appears, if a php file references 100 objects, then this file needs to use include or require to introduce 100 objects. class file, which will cause the php file to be extremely large. So there is this __autoload function.
When is the __autoload function called?
When the new keyword is used in the PHP file to instantiate an object, if the class is not defined in the PHP file, the __autoload function will be triggered. At this time, the definition of the class can be introduced. php file, and then it can be instantiated successfully. (Note: If the object that needs to be instantiated has been found in this file and the definition of the class has been found, the __autoload function will not be triggered)
#Animal.php<?php class Animal{}?>
#main.php<?php function __autoload($classname){ $classpath = "{$classname}.php"; if(file_exists($classpath)){ require_once($classpath); }else{ echo $classpath." not be found!"; } } $ani = new Animal();?>
Like the above two files, run php main.php
(1) When running to new Animal(), it is found that class Animal is not defined;
(2) The __autoload function is triggered, which introduces the Animal.php file;
(3) The instantiation is successful.
Okay, after understanding the role of the __autoload function, let’s take a look at the role of the spl_autoload_register function.
The role of the spl_autoload_register function is to replace the custom function settings with the __autoload function (note: when __autoload and spl_autoload_register appear in the file at the same time, spl_autoload_register shall prevail)
Then changing main.php to the following will have the same effect Role:
#main.php<?php function myLoad($classname){ $classpath = "{$classname}.php"; if(file_exists($classpath)){ require_once($classpath); }else{ echo $classpath." not be found!"; } } spl_autoload_register("myLoad"); $ani = new Animal();?>
The above is the detailed content of Detailed explanation of two PHP automatic loading functions. For more information, please follow other related articles on the PHP Chinese website!

php把负数转为正整数的方法:1、使用abs()函数将负数转为正数,使用intval()函数对正数取整,转为正整数,语法“intval(abs($number))”;2、利用“~”位运算符将负数取反加一,语法“~$number + 1”。

实现方法:1、使用“sleep(延迟秒数)”语句,可延迟执行函数若干秒;2、使用“time_nanosleep(延迟秒数,延迟纳秒数)”语句,可延迟执行函数若干秒和纳秒;3、使用“time_sleep_until(time()+7)”语句。

php除以100保留两位小数的方法:1、利用“/”运算符进行除法运算,语法“数值 / 100”;2、使用“number_format(除法结果, 2)”或“sprintf("%.2f",除法结果)”语句进行四舍五入的处理值,并保留两位小数。

判断方法:1、使用“strtotime("年-月-日")”语句将给定的年月日转换为时间戳格式;2、用“date("z",时间戳)+1”语句计算指定时间戳是一年的第几天。date()返回的天数是从0开始计算的,因此真实天数需要在此基础上加1。

php判断有没有小数点的方法:1、使用“strpos(数字字符串,'.')”语法,如果返回小数点在字符串中第一次出现的位置,则有小数点;2、使用“strrpos(数字字符串,'.')”语句,如果返回小数点在字符串中最后一次出现的位置,则有。

php字符串有下标。在PHP中,下标不仅可以应用于数组和对象,还可应用于字符串,利用字符串的下标和中括号“[]”可以访问指定索引位置的字符,并对该字符进行读写,语法“字符串名[下标值]”;字符串的下标值(索引值)只能是整数类型,起始值为0。

方法:1、用“str_replace(" ","其他字符",$str)”语句,可将nbsp符替换为其他字符;2、用“preg_replace("/(\s|\ \;||\xc2\xa0)/","其他字符",$str)”语句。

在php中,可以使用substr()函数来读取字符串后几个字符,只需要将该函数的第二个参数设置为负值,第三个参数省略即可;语法为“substr(字符串,-n)”,表示读取从字符串结尾处向前数第n个字符开始,直到字符串结尾的全部字符。


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