Detailed explanation of PHP require/include sequence_PHP tutorial

php tutorial require/include sequence detailed explanation

In large web projects, include_path is the foundation of modular design (of course, there are also many designs based on autoload, which does not affect the discussion of this article), but it is precisely because of include_path that we often I encountered some seemingly "weird" problems caused by not finding the correct file. I also had the following questions: How does include_path work? What is the order if there are multiple include_paths? Under what circumstances include_path Doesn’t work? Today, I will give a comprehensive introduction to this problem, starting with an example. The following directory structure: root 1.php 3.php subdir 2.php                                3.php in 1.php:
Copy the code. The code is as follows:
ini_set("include_path", ".:path_to_subdir");
require("2.php");
?>And in 2.php:
Copy the code. The code is as follows:
require("3.php");
?> And 3.php in the root directory prints "root", and 3.php in the subdir directory prints "subdir"; now, here comes my question:
1. When running 1.php in the root directory, what output will you get?
2. Run 1.php in the upper directory under subdir. What output will you get?
3. When canceling the current directory path in include_path (that is, include_path="path_to_subdir"), what will be the output of the above two questions?
include_path in php
When PHP encounters the require(_once)/include(_once) instruction, it will first make the following judgment:
Copy the code. The code is as follows:
Is the file path to be included an absolute path?
If so, include it directly and end.
If not, enter another logic (after multiple calls, enter _php_stream_fopen_with_path after macro expansion) to find this file. Next, in _php_stream_fopen_with_path, the following judgment will be made:
Copy the code. The code is as follows:
Is the file path to be included a relative path (in the form of ./file, ../dir/file, replaced by "directory relative path" below)?
If so, skip the logic of include_path and directly parse the relative path (introduced separately later). A list of directories to be selected will be formed based on include_path and the path of the currently executed file. For example, for the example in the previous article, a directory list will be formed. The following waiting list
Copy the code. The code is as follows:
".:path_to_subdir:current_script_dir Then, starting from the head of the candidate list, take out a path in the candidate list according to default_dir_separator (the environment of this article is ":"), and then append the file name to be included to the end of this path. Make an attempt. If included successfully, return, otherwise continue with the next candidate path.
So far, we can answer the 3 questions I asked at the beginning.
1. Because it is executed in the root directory, when 2.php is included in 1.php, the second candidate path of include_path works (path_to_subdir), and path_to_subdir/2.php is found, while in 2.php When 3.php is included, the current working directory is under root, so when 3.php is included, the matching file is found in the first candidate path of include_path "." (current working directory), so we get The output is "root".
2. Same as 1, except that the current path is subdir, so the output is "subdir".
3. Because there is no include_path in the current path, when 2.php includes 3.php when running in the root directory, path_to_subdir plays a role, so you will get the output of "subdir" whether in root or subdir.
And if you clear include_path in 2.php,
Copy the code. The code is as follows:
ini_set("include_path", '');
require("3.php");
?>Then current_script_dir will take effect, and at this time current_script_dir is the path of 2.php, so you will still get the output of "subdir".
Directory relative path
When using a directory relative path, the base point of the relative path is always the current working directory.
In order to illustrate the situation under the relative path of the directory, let's look at another example. It is still the above directory structure, but 1.php becomes:
Copy the code. The code is as follows:
ini_set("include_path", "/");
require("./subdir/2.php");
?>2.php becomes:
Copy the code. The code is as follows:
require("./3.php");
?>If executed in the root directory, searching for 3.php in 2.php will be searched in the relative path of the current directory, so the output obtained is "root", and if executed in the subdir of the upper-level directory 1.php(php -f ../1.php), will exit abnormally because "./subdir/2.php" cannot be found under subdir.
Postscript
1. Because when using include_path and relative paths, performance will be related to the number of searches. In the worst case, if you have 10 include_paths, you may have to retry up to 11 times to find the file to be included. Therefore, It is best to use absolute paths when possible.
2. Because the basedir of the directory relative path is always the current working path, if it is to be used, it needs to be related to the actual deployment path, so it is rarely used in practice (of course, there are also modules that use chdir to complete it).
3. In modular system design, the absolute path should generally be used within the module by obtaining the deployment path of the module (dirname(__file__), php5.3 and later provides the __dir__ constant).

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