In-depth understanding of PHP's require/include sequence Recommended_PHP Tutorial

There are also the following questions:

How does include_path work?

What is the order if there are multiple include_paths?

Under what circumstances does include_path not work?

Today, I will give a comprehensive introduction to this issue, starting with an example.

The following directory structure:

<ol>
<li>  root</li>
<li>    ├ <span class="sh_number">1</span><span class="sh_symbol">.</span>php</li>
<li>    ├ <span class="sh_number">3</span><span class="sh_symbol">.</span>php</li>
<li>    └ subdir</li>
<li>         ├ <span class="sh_number">2</span><span class="sh_symbol">.</span>php</li>
<li>          └ <span class="sh_number">3</span><span class="sh_symbol">.</span>php</li>
</ol>

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 code The code is as follows:

require("3.php");
?>

The 3.php in the root directory prints "root", and the 3.php in the subdir directory prints "subdir";

Now, here are my questions:
1. When running 1.php in the root directory, what output will you get?
2. When running 1.php in the upper directory under subdir, there will be What output will be obtained?
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 require(_once)/include(_once) instructions, it will first make the following judgment:

Copy code Code 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, After the macro is expanded, enter _php_stream_fopen_with_path) to look for this file

Next, in _php_stream_fopen_with_path, the following judgment will be made:

Copy 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)

will form a list of directories to be selected based on include_path and the path of the current execution file, such as for articles For the previous example, a candidate list will be formed as follows:

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 After this path, try. If successfully included, return, otherwise continue to the next candidate path.
Up to now, we can answer the 3 questions I raised at the beginning.
1. Because in It is executed in the root directory, so when 2.php is included in 1.php, the second candidate path of include_path works (path_to_subdir), path_to_subdir/2.php is found, and 2.php includes 3.php. When , the current working directory is under root, so when 3.php is included, the matching file is found under the first candidate path of include_path "." (current working directory), so the output obtained 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 running in the root directory 2. When 3.php is included in php, path_to_subdir plays a role, so whether in root or subdir, you will get the output of "subdir".
And if you clear include_path in 2.php,

Copy 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 directory relative path, the base point of the relative path is always the current working directory.
To illustrate the situation under directory relative path, let’s look at it again For example, the directory structure above is still the same, except that 1.php has become:

Copy the code The code is as follows:

ini_set("include_path", "/");
require("./subdir/2.php");
?>

2 .php becomes:

Copy 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 an absolute path when an absolute path can be used.
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 are completed with the help of chdir).
3. In modular system design, it should generally be obtained within the module by obtaining the deployment path of the module (dirname(__FILE__), which is provided after php5.3 __DIR__ constant) to use absolute paths.

http://www.bkjia.com/PHPjc/322704.htmlwww.bkjia.comtruehttp: //www.bkjia.com/PHPjc/322704.htmlTechArticleThere are also the following questions: How does include_path work? What is the order if there are multiple include_paths? ? Under what circumstances does include_path not work? Today, I will give a comprehensive introduction...