PHP: require and include path issues

FILE is a preprocessed variable, processed before running, and has been replaced before the file is included.
The content of the file required include is processed at runtime, and its code is run in the space of the included file, a relative path, relative to the included file.

1 Absolute path, relative path and undetermined path

Relative path

Relative path refers to the path starting with ., such as

./a/ a.php (relative to the current directory)
../common.inc.php (relative to the upper-level directory),

absolute path

The absolute path starts with / or windows C:/ similar to the path starting with the drive letter, the full path can uniquely determine the final address of the file without any reference path. For example

/apache/wwwroot/site/a/a.php
c:/wwwroot/site/a/a.php

Undetermined path

Any path that does not start with . or /, nor does it start with the Windows drive letter:/, such as

a/a.php
common.inc.php,

At first I thought this was also a relative path, but in PHP's include/require inclusion mechanism, this type of path is handled completely differently from relative paths starting with . require './a.php' and require 'a.php' are different!

Let’s analyze the processing methods of these three types of include paths: First, remember a conclusion: if the include path is a relative path or an absolute path, it will not go to include_path (the include_path environment variable defined in php.ini, Or use set_include_path(...) to find the file in the program.

Test environment description

Note: The following discussion and conclusion are based on this environment: Assume A=http://www.xxx.com/app/test/a.php, emphasize again The following discussion is for the case of direct access to A.

2. Relative path:

The relative path requires a reference directory to determine the final path of the file. In include parsing, no matter how many levels of nesting are included, this reference directory is the program execution Entry file directory.

Example 1

A defines require './b/b.php'; // then B=[SITE]/app/test/b/b.php
B Definition require './c.php'; // Then C=[SITE]/app/test/c.php is not [SITE]/app/test/b/c.php

Example 2

A defines require './b/b.php'; // Then B=[SITE]/app/test/b/b.php
B defines require '.. /c.php'; // Then C=[SITE]/app/c.php is not [SITE]/app/test/c.php

Example 3

A defines require '../b.php'; //then B=[SITE]/app/b.php
B defines require '../c.php'; //then C= [SITE]/app/c.php is not [SITE]/c.php

Example 4:

A defines require '../b.php' ; // Then B=[SITE]/app/b.php
Define require './c/c.php' in B; // Then C=[SITE]/app/test/c/c.php Not [SITE]/app/c/c.php

As defined in Example 5

A require '../inc/b.php'; // then B=[SITE]/app/inc/b.php
B requires require './c/c.php'; // Then C still =[SITE]/app/test/c/c.php No [SITE]/app/inc/c/c.php

Example 6

A defines require '../inc/b.php'; // Then B=[SITE]/app/inc/b.php
B requires require './c.php'; // Then C=[SITE]/app/test/c.php is not [SITE]/ app/inc/c.php

3. Absolute path

The absolute path is relatively simple and not easy to cause confusion and errors. require|inclue corresponds to the file on the disk. .

require '/wwwroot/xxx.com/app/test/b.php'; // In Linux
require 'c:/wwwroot/xxx.com/app/test/b.php' ; // In windows,

dirname(FILE) is also calculated as a directory in the form of an absolute path, but please note that FILE is a Magic constants, which is equal to The absolute path of the PHP file where this statement is written. Therefore, dirname(FILE) always points to the absolute path of the PHP file where this statement is written. It has nothing to do with whether this file is included and used by other files.

Example 1

A defines require '../b.php'; FILE).'/c.php'; // Then B=[SITE]/app/c.php

Example 2

Define require '../inc/b.php'; in A php'; // Then B=[SITE]/app/inc/c.php is always in the same directory as B

Conclusion: No matter whether B is included and used by A, or directly accessed

Bif require dirname(FILE).'/c.php'; // always refers to the c.php file in the same directory as B;

Bif require dirname(FILE). '/../c.php'; // Always reference the c.php file in the parent directory of the directory where the B file is located;
BIf require dirname(FILE).'/c/c.php'; // Then always refer to the c.php file in the c subdirectory of the directory where the B file is located;

4. Undetermined path

First use the includes defined in include_path one by one Directory to splice [undetermined path]. If an existing file is found, it will include successful exit. If it is not found, use the directory where the php file that executes the require statement is located to splice the full path composed of [undetermined path] to find the file. If the file If it exists, it means successful exit, otherwise it means the included file does not exist and an error occurs. Undetermined paths are easy to confuse and are not recommended.

5. Solution

Since the "reference directory" in "relative path" is the directory where the execution entry file is located, the "undetermined" path is also easier to confuse, so the best solution is It is to use the "absolute path"; for example, the content of b.php is as follows. No matter where b.php is required, the path of b.php is used as a reference to require c.php

$dir = dirname(FILE );

require($dir . '../c.php');

Or define a general function import.php, set it to "automatically import files in advance", in Make the following configuration in php.ini

Change the configuration item (required) auto_prepend_file = "C:\xampp\htdocs\auto_prepend_file.php"

Change the configuration item (optional) allow_url_include = On

The content of import.php is as follows

function import($path) {    
    $old_dir = getcwd();        // 保存原“参照目录”
    chdir(dirname(FILE));    // 将“参照目录”更改为当前脚本的绝对路径
    require_once($path);
    chdir($old_dir);            // 改回原“参照目录”
}

In this way, you can use the import() function to require the file. No matter how many levels of "reference directories" it contains, it is the current file

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