PHP's doubts about class_exists function and Auto-loading Mechanism

1. The default implementation function spl_autoload () of autoload cannot be activated when the spl_autoload_register function is not called. How does the automatic loading mechanism of PHP run if the user does not define the _ _ autoload () function?
2. In the above case, if you use the class_exists function without changing the default parameter to false to call _ _ autoload (), how does php handle it?
3. Does PHP have a default implementation of the _ _ autoload () function in the first case? What is the default implementation mechanism?
4. What is the internal implementation mechanism of spl_autoload ()?

Please ask all the great gods to answer questions and questions. Thank you very much

Php
Jun.02,2022

1 will find
2 in the current command space by default. If the class has been loaded in the same space, it will report an error. If not, loading
3 means that the spl class library implements _ _ autoload, which is compatible with multiple loading methods. http://php.net/manual/zh/func...

MySQL Query : SELECT * FROM `codeshelper`.`v9_news` WHERE status=99 AND catid='6' ORDER BY rand() LIMIT 5
MySQL Error : Disk full (/tmp/#sql-temptable-64f5-1bf854d-320d7.MAI); waiting for someone to free some space... (errno: 28 "No space left on device")
MySQL Errno : 1021
Message : Disk full (/tmp/#sql-temptable-64f5-1bf854d-320d7.MAI); waiting for someone to free some space... (errno: 28 "No space left on device")
Need Help?