Require, require in PHP_ once、include、include_ Detailed explanation of the efficiency of repeated introduction of once class library

include() And require() The same function

The only difference ：require() Whether executed or not , As long as there is a ,php It will be pre introduced before execution ,include() It is not introduced until the statement is executed

include_once() And require_once() Is to detect whether the file is imported , If it is introduced, it will not be introduced

The only difference ： require_once() Unconditionally include , As the name suggests, that is, stop if there is an error after the introduction ,include_once() Then ignore and continue

On efficiency , I want to explain , Please consciously use less include_once()、 require_once()

The principle of this function ： The introduction of the file -> Compare whether the current script statement contains -> Decide whether to introduce , Efficiency is conceivable , You think if you have hundreds of class libraries in the whole project , How terrible is it to compare dozens of times in one execution

Here is a solution to prevent the repeated introduction of files in personal multi class libraries ：

1. In the calling script, use require();

2. Prevent reuse in class libraries class_exists(‘ Class name ’) or include(‘ Absolute path of class library ’);

explain ： The file that calls the script is used once require(), Because the calling script is the general entry of the program , The introduction of public class libraries here rarely results in public class libraries not being used , Use the above statement in the class library , It can prevent the current script from repeatedly introducing the public class library , And only by judging the conditions can the introduction be executed , Pre import will not be repeated , Improve the efficiency of program execution