常量-PHP Tutorial-php.cn

Home

Backend Development

PHP Tutorial

常量

WBOYWBOYWBOYWBOYWBOYWBOYWBOYWBOYWBOYWBOYWBOYWBOYWB

Jun 23, 2016 pm 01:39 PM

常量语法

常量在脚本执行期间其值不能改变。常量大小写敏感，传统上常量标识符总是大写。常量一旦定义就不能被重新定义或取消定义，常量的值只能是标量。

可以用define()函数来定义常量，也可以使用const关键字在类定义之外定义常量。自定义常量不要以双下划线开头，可能会与魔术常量冲突。

define('FOO', 'something');const FOO = 'something';

使用const关键字定义常量必须处于最顶端的作用区域，因为用此方法是在编译时定义的。常量的范围是全局的，不用管作用区域，就可以在脚本的任何地方访问常量。

魔术常量

魔术常量值能变，但它其实不是常量。

PHP向它运行的任何脚本提供了大量的预定义常量，有8个魔术常量的值随着它们在代码中的位置改变而改变。

__LINE__  // 文件中的当前行号__FILE__  // 文件的完整路径和文件名，绝对路径__DIR__  // 文件所在的目录，除非根目录，否则不包括末尾斜杠，等价于dirname(__FILE__)__FUNCTION__  // 函数名称，区分大小写__CLASS__  // 类的名称，包括其被声明的作用区域__TRAIT__  // Trait的名字，包括其被声明的作用区域__METHOD__  // 类的方法名__NAMESPACE__  // 当前命名空间的名称

这几个魔术常量也不知什么作用，就先放在这里吧。

（全文完）

Statement

The content of this article is voluntarily contributed by netizens, and the copyright belongs to the original author. This site does not assume corresponding legal responsibility. If you find any content suspected of plagiarism or infringement, please contact admin@php.cn

Working with Flash Session Data in LaravelMar 12, 2025 pm 05:08 PM

Laravel simplifies handling temporary session data using its intuitive flash methods. This is perfect for displaying brief messages, alerts, or notifications within your application. Data persists only for the subsequent request by default: $request-

cURL in PHP: How to Use the PHP cURL Extension in REST APIsMar 14, 2025 am 11:42 AM

The PHP Client URL (cURL) extension is a powerful tool for developers, enabling seamless interaction with remote servers and REST APIs. By leveraging libcurl, a well-respected multi-protocol file transfer library, PHP cURL facilitates efficient execution of various network protocols, including HTTP, HTTPS, and FTP. This extension offers granular control over HTTP requests, supports multiple concurrent operations, and provides built-in security features.

Simplified HTTP Response Mocking in Laravel TestsMar 12, 2025 pm 05:09 PM

Laravel provides concise HTTP response simulation syntax, simplifying HTTP interaction testing. This approach significantly reduces code redundancy while making your test simulation more intuitive. The basic implementation provides a variety of response type shortcuts: use Illuminate\Support\Facades\Http; Http::fake([ 'google.com' => 'Hello World', 'github.com' => ['foo' => 'bar'], 'forge.laravel.com' =>

Discover File Downloads in Laravel with Storage::downloadMar 06, 2025 am 02:22 AM

The Storage::download method of the Laravel framework provides a concise API for safely handling file downloads while managing abstractions of file storage. Here is an example of using Storage::download() in the example controller:

12 Best PHP Chat Scripts on CodeCanyonMar 13, 2025 pm 12:08 PM

Do you want to provide real-time, instant solutions to your customers' most pressing problems? Live chat lets you have real-time conversations with customers and resolve their problems instantly. It allows you to provide faster service to your custom

Explain the concept of late static binding in PHP.Mar 21, 2025 pm 01:33 PM

Article discusses late static binding (LSB) in PHP, introduced in PHP 5.3, allowing runtime resolution of static method calls for more flexible inheritance.Main issue: LSB vs. traditional polymorphism; LSB's practical applications and potential perfo

PHP Logging: Best Practices for PHP Log AnalysisMar 10, 2025 pm 02:32 PM

PHP logging is essential for monitoring and debugging web applications, as well as capturing critical events, errors, and runtime behavior. It provides valuable insights into system performance, helps identify issues, and supports faster troubleshoot

How to Register and Use Laravel Service ProvidersMar 07, 2025 am 01:18 AM

Laravel's service container and service providers are fundamental to its architecture. This article explores service containers, details service provider creation, registration, and demonstrates practical usage with examples. We'll begin with an ove

See all articles