php 为什么在 require_once 中包含 __DIR__？
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Why include __DIR__ in the require_once?
提问by Dan Goodspeed
For example, I always see autoloaders called like this:
例如，我总是看到像这样调用自动加载器：
require_once __DIR__ . '/../vendor/autoload.php';
What is the difference between that and the more concise
那和更简洁有什么区别
require_once '../vendor/autoload.php';
?
?
回答by Evert
PHP scripts run relative to the current path (result of getcwd()), not to the path of their own file. Using __DIR__forces the include to happen relative to their own path.
PHP 脚本相对于当前路径（ 的结果getcwd()）运行，而不是相对于它们自己文件的路径。使用__DIR__强制包含相对于它们自己的路径发生。
To demonstrate, create the following files (and directories):
为了演示，创建以下文件（和目录）：
- file1.php
- dir/
- file2.php
- file3.php
If file2.phpincludes file3.phplike this:
如果file2.php包括file3.php这样的：
include `file3.php`.
It will work fine if you call file2.phpdirectly. However, if file1.phpincludesfile2.php, the current directory (getcwd()), will be wrong for file2.php, so file3.phpcannot be included.
如果你file2.php直接打电话，它会工作得很好。但是，如果file1.php包含file2.php，当前目录 ( getcwd()) 将是错误的file2.php，因此file3.php无法包含。
回答by René H?hle
For include its possible to set some folders where PHP search automatically. When you include a file with a relative path you search in all of that folders. Its better to define the real path to prevent some errors in loading wrong files.
对于 include 可以设置一些 PHP 自动搜索的文件夹。当您包含具有相对路径的文件时，您将在所有文件夹中进行搜索。最好定义真实路径，以防止加载错误文件时出现一些错误。
https://secure.php.net/manual/en/function.set-include-path.php
https://secure.php.net/manual/en/function.set-include-path.php
Then you can be sure that you load the correct file.
然后您可以确定您加载了正确的文件。
