Require_once a strange phenomenon, everybody, look.

Require_once a strange phenomenon, everybody look down
I am in the root directory of the file require_once ("test/1.php"); Then in 1.php require_once ("2.php");
Case 1, if my root directory exists 2.php program will go to reference the root directory of 2.php
Case 2, if my root directory does not exist 2.php, the program will also refer to the test directory of 2.php
Do not know why there is a situation of 2, we have encountered it, what is the reason?
Require_once is not the first page in the main path?



------to solve the idea----------------------
Include (include_once, require, require_once) to execute the file as the benchmark
Find files by the path indicated by include_path
Generally include_path = ".:/ Path1:/path2 "(UNIX) or include_path =".; \ Path1;\path2 "(window)
The.,/path1,/path2 .... The Sequential lookup

So the order of the search is: the directory where the program is executed, the directory where the files are contained, and the other directories specified by include_path

The advantage of this design is that you can change some behavior of the original project without having to modify the original project

index.php (require_once ("test/1.php");)
test/1.php (require_once ("2.php");)
test/2.php
2.php (this 2.php will replace test/2.php)

