使用__DIR__ 優(yōu)於dirname(__FILE__)，因為__DIR__ 更簡潔、安全且高效。 1. __DIR__ 是PHP 5.3 引入的魔法常量，直接返回當前文件的絕對目錄路徑，無需函數(shù)調(diào)用；2. 相比dirname(__FILE__)，它減少字符串解析，避免潛在路徑拼接錯誤；3. 推薦用__DIR__ 構(gòu)建相對路徑，如__DIR__ . '/config.php'；4. 需要上級目錄時可嵌套使用dirname(__DIR__)；5. 儘管Composer 自動加載減少了手動引入的需求，但在配置文件、常量定義和引導(dǎo)文件中__DIR__ 仍廣泛適用；6. 最佳實踐包括避免__FILE__ 用於目錄解析，優(yōu)先使用自動加載，並考慮更健壯的路徑處理工具。因此，應(yīng)停止使用dirname(__FILE__)，改用__DIR__ 以提升代碼可讀性與維護性。

Using __FILE__ and __DIR__ in PHP might seem like a small detail, but the shift from __FILE__ to __DIR__ reflects a broader move toward cleaner, more maintainable code — a modern PHP best practice.

Back in older PHP projects (especially pre-PHP 5.3 or before PSR standards became widespread), you'd often see code like this:

 require_once dirname(__FILE__) . '/config.php';
include __FILE__ . '/../lib/helpers.php';

This pattern was standard for building file paths relative to the current script. But it's clunky, error-prone, and harder to read.

Why __DIR__ Is Better Than dirname(__FILE__)

Starting with PHP 5.3, __DIR__ was introduced as a magic constant that returns the directory of the current file — no function call needed.

So this:

 dirname(__FILE__)

becomes simply:

 __DIR__

That means:

 require_once dirname(__FILE__) . '/config.php';

can now be written as:

 require_once __DIR__ . '/config.php';

It's shorter, clearer, and slightly more efficient (no function call).

Cleaner, Safer, and More Predictable

Using __DIR__ removes ambiguity. dirname(__FILE__) relies on a function call to parse a string, which, while reliable in most cases, adds an unnecessary layer. __DIR__ is resolved at compile time and always gives you the absolute path to the directory — no string manipulation, no edge cases.

Also, consider this subtle bug:

 __FILE__ . '/../config.php' // Oops! Missing slash? Result: '/file.php../config.php'

But with __DIR__ , you're starting from a known directory path:

 __DIR__ . '/../config.php' // Much clearer and easier to reason about

Even better? Use realpath() or dirname(__DIR__) for parent directories in a cleaner way:

 require_once dirname(__DIR__) . '/vendor/autoload.php';

This is especially common in bootstrapping files or entry points like public/index.php .

Autoloading Made It Less Necessary — But Still Relevant

With modern PHP using Composer and PSR-4 autoloading, direct include or require statements are far less common. You rarely need to manually load class files.

However, there are still valid use cases for __DIR__ :

• Loading configuration files
• Setting up constants for paths
• Registering plugins or modules in a directory
• Building asset paths in CLI or framework bootstraps

Example from a real-world index.php :

 define('APP_ROOT', __DIR__);
require_once __DIR__ . '/../vendor/autoload.php';
$config = require __DIR__ . '/config/app.php';

These patterns are still current — just cleaner with __DIR__ .

Best Practices Summary

• ? Use __DIR__ instead of dirname(__FILE__) — it's shorter and safer
• ? Prefer autoloading over manual require when possible
• ? Use dirname(__DIR__) to reference parent directories (common in public/ subfolders)
• ? Avoid string-concatenated paths when tools like pathinfo() or filesystem components exist
• ? Don't use __FILE__ for directory resolution — it's outdated for that purpose

Basically, if you're still typing dirname(__FILE__) , it's time to switch. __DIR__ has been around for over a decade — it's not "new," but it is part of writing modern, readable PHP.

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