require_once Explanation of the difference between include and require in PHP

require is used like <font face="NSimsun">require("MyRequireFile.php");</font> . This function is usually placed at the front of the PHP program. Before the PHP program is executed, it will first read in the file specified by require and make it a part of the PHP program web page. Commonly used functions can also be introduced into web pages in this way.

include Usage method such as <font face="NSimsun">include("MyIncludeFile.php");</font>. This function is generally placed in the processing part of flow control. The PHP program webpage only reads the include file when it reads it. In this way, the process of program execution can be simplified.
The two of them have exactly the same purpose, and it doesn’t necessarily have to be which one is placed at the front and which one is placed in the middle. The most fundamental difference between them is the way they handle errors.
If there is an error in a require file, the program will interrupt execution and display a fatal error.
If there is an error in include a file, the program will not terminate but will continue to execute and display a warning error.
The following are supplements:
1. include has a return value, but require does not.
2. include() includes and runs the specified file. When the processing fails, include() generates a warning. The imported program code will be executed, and these programs will have the include() statement called in the source file when executed. position in the same variable scope. You can import static pages from the same server.
3. The function of include_once() is almost the same as include(). The only difference is that include_once() will first check whether the file to be imported has been imported elsewhere in the program. If so, (This function is sometimes very important. For example, if the file you want to import declares some functions that you have defined yourself, then if you import this file repeatedly in the same program, the file will be imported for the second time. The error message will occur because PHP does not allow functions with the same name to be declared a second time).
4. require() will read the contents of the target file and replace itself with the read contents. If the processing fails, require() will cause a fatal error.
This reading and substitution action occurs when the PHP engine compiles your program code, not when the PHP engine starts executing the compiled program code (the way the PHP 3.0 engine works is to compile and execute one line at a time , but things have changed since PHP 4.0. PHP 4.0 first compiles the entire program code, and then executes the compiled program code at once. No program code will be executed during the compilation process). require() is usually used to import static content, while include() is suitable for importing dynamic program code.
5. Like include_once(), require_once() will first check whether the content of the target file has been imported before. If so, the same content will not be imported again.
5. require is an unconditional inclusion, that is, if require is added to a process, require will be executed first regardless of whether the condition is true or not.
7. require is usually placed at the front of the PHP program. Before the PHP program is executed, it will first read in the file specified by require and make it a part of the PHP program web page. Commonly used functions can also be introduced into web pages in this way.
8. Include is generally placed in the processing part of the process control. The PHP program webpage only reads the included file when it reads it. This method can simplify the process of program execution.
The difference between require(), include(), require_once() and include_once()

The above has introduced require_once the difference between include and require in PHP, including the content of require_once. I hope it will be helpful to friends who are interested in PHP tutorials.