Code examples of require and include path problems in php

This article mainly introduces the detailed explanation of require and include path issues in PHP. It is very detailed. Friends who need it can refer to

1 Absolute path, relative path and unspecified path. Determine the path

Relative path

The relative path refers to the path starting with ., for example

The code is as follows:

./a/a.php (相对当前目录)    
../common.inc.php (相对上级目录)，

Absolute path

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

code is as follows:

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

Undetermined path

Anything that does not start with . or /, nor does it start with the Windows drive letter:/ Path, for example

The code is as follows:

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 processed the same as the relative path starting with . is completely different. 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 Execute the directory where entry file is located.

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

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

As defined in Example 3

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

Example 4:

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

Example 5

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

Example 6

A defines require '../inc/b.php'; // Then B=[SITE]/app/inc/b.php
B defines 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 less likely to cause confusion and error. 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 php that writes this statement at any time. The absolute path where the file is located, so dirname(FILE) always points to the absolute path of the php file where this statement is written, and has nothing to do with whether the file is included and used by other files.

Example 1

Define in A require '../b.php'; // Then B=[SITE]/app/b.php
Define in B require dirname( FILE).'/c.php'; // Then B=[SITE]/app/c.php

Example 2

A defines require '../inc/b. php'; // Then B=[SITE]/app/inc/b.php
is defined in B require dirname(FILE).'/c.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

B如果 require dirname(FILE).'/c.php';    // 则始终引用到跟B在同一个目录中的 c.php文件;
B如果 require dirname(FILE).'/../c.php'; // 则始终引用到B文件所在目录的父目录中的 c.php文件;
B如果 require dirname(FILE).'/c/c.php';  // 则始终引用到B文件所在目录的c子目录中的 c.php文件;

4. 未确定路径

首先在逐一用include_path中定义的包含目录来拼接[未确定路径]，找到存在的文件则包含成功退出，如果没有找到，则用执行require语句的php文件所在目录来拼接[未确定路径]组成的全路径去查找该文件，如果文件存在则包含成功退出，否则表示包含文件不存在，出错。 未确定路径比较容易搞混不建议使用。

5. 解决方案

由于“相对路径”中的“参照目录”是执行入口文件所在目录，“未确定”路径也比较容易混淆，因此最好的解决方法是使用“绝对路径”; 例如b.php的内容如下，无论在哪里require b.php都是以b.php的路径为参照来require c.php的

$dir = dirname(FILE);
require($dir . '../c.php');
或者定义一个通用函数 import.php，将其设置为“自动提前引入文件”，在php.ini做如下配置

更改配置项（必须）auto_prepend_file = "C:\xampp\htdocs\auto_prepend_file.php"
更改配置项（可选）allow_url_include = On

import.php内容如下

代码如下:

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”
}

这样就可以使用import()函数来require文件了，无论包含多少级“参照目录”都是当前文件

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