Home php教程 php手册 如何正确理解PHP include作用域

如何正确理解PHP include作用域

Jun 13, 2016 am 11:11 AM
include php Scope use exist based on how document Notice programmer

很多程序员在使用

注意:本文档基于include叙述,但也适用于 require。这两种结构除了在如何处理包含失败之外,其他完全一样:在包含失败时,include()产生一个警告并继续执行,而require()则导致一个致命错误。换句话说,如果想在遇到丢失文件时停止处理页面就用require(),否则就用include()。

PHP include作用域1、c

<ol class="dp-xml">
<li class="alt"><span><span class="tag"><span> ?php  </span></span></span></li>
<li>
<span>$</span><span class="attribute">color</span><span> = </span><span class="attribute-value">'green'</span><span>;  </span>
</li>
<li class="alt">
<span>$</span><span class="attribute">fruit</span><span> = </span><span class="attribute-value">'apple'</span><span>;  </span>
</li>
<li>
<span class="tag">?></span><span> </span>
</li>
</ol>
Copy after login
<ol class="dp-xml">
<li class="alt"><span><span class="tag"><span> ?php  </span></span></span></li>
<li><span>function foo()  </span></li>
<li class="alt"><span>{  </span></li>
<li><span>global $color;  </span></li>
<li class="alt"><span>include 'vars.php';  </span></li>
<li><span>echo "A $color $fruit";  </span></li>
<li class="alt"><span>}  </span></li>
<li><span>foo();   </span></li>
<li class="alt"><span>// A green apple  </span></li>
<li><span>echo "A $color $fruit";   </span></li>
<li class="alt"><span>// A green  </span></li>
<li>
<span class="tag">?></span><span>  </span>
</li>
</ol>
Copy after login

由此例可看出:

(1) 被包含文件的变量的PHP include作用域遵从包含文件所在处的作用域。即在函数里使用include将其他文件的变量包含进来,这些变量的作用域为该函数内。

(2) foo()函数外能打印出$color的值,并没有违反(1)的规定。那是因为函数开始已经声明$color为global (尽管foo()函数外并没有$color变量,此时的$color变量并不是vars.php里面的$color变量,而是一个强制声明为“全局”的新变量,这时它还没有被赋值,当下面包含进vars.php后,根据(1)的原则,vars.php中的$color变量自动享有函数内的作用域,所以它的值就是全局变量$color的值)

PHP include作用域2、函数、类的作用域

<ol class="dp-xml">
<li class="alt"><span><span class="tag"><span> ?php  </span></span></span></li>
<li><span>class ClassB {  </span></li>
<li class="alt"><span>/**  </span></li>
<li><span>* constructor  </span></li>
<li class="alt"><span>*/  </span></li>
<li><span>public function __construct(){}  </span></li>
<li class="alt"><span>/**  </span></li>
<li><span>* destructor  </span></li>
<li class="alt"><span>*/  </span></li>
<li><span>public function __destruct() {}  </span></li>
<li class="alt"><span>public function printit() {  </span></li>
<li>
<span>echo 'print it in ClassB.</span><span class="tag"><span class="tag-name">br</span><span> </span><span class="tag">/></span><span>';  </span></span>
</li>
<li class="alt"><span>}   </span></li>
<li><span>}  </span></li>
<li class="alt"><span>function show_func_included() {  </span></li>
<li>
<span>echo 'show_func_included</span><span class="tag"><span class="tag-name">br</span><span class="tag">/></span><span>';  </span></span>
</li>
<li class="alt"><span>}  </span></li>
<li>
<span class="tag">?></span><span> </span>
</li>
</ol>
Copy after login
<ol class="dp-xml">
<li class="alt"><span><span class="tag"><span> ?php  </span></span></span></li>
<li><span>function include_class() {  </span></li>
<li class="alt"><span>include('classb.php');  </span></li>
<li><span>}  </span></li>
<li class="alt"><span>include_class();  </span></li>
<li>
<span>$</span><span class="attribute">objB</span><span> = </span><span class="attribute-value">new</span><span> ClassB();  </span>
</li>
<li class="alt">
<span>$objB-</span><span class="tag">></span><span>printit();   </span>
</li>
<li><span>// print it in ClassB.  </span></li>
<li class="alt"><span>show_func_included()   </span></li>
<li><span>// show_func_included  </span></li>
<li class="alt">
<span class="tag">?></span><span>  </span>
</li>
</ol>
Copy after login

由此例可以看出

所有在被包含文件中定义的函数和类在被包含后,在包含文件里都具有全局作用域

结论:

1、被包含文件的变量的PHP include作用域遵从(不改变)包含文件所在处的作用域。
2、所有在被包含文件中定义的函数和类在被包含后,在包含文件里都具有全局作用域


Statement of this Website
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

Hot AI Tools

Undresser.AI Undress

Undresser.AI Undress

AI-powered app for creating realistic nude photos

AI Clothes Remover

AI Clothes Remover

Online AI tool for removing clothes from photos.

Undress AI Tool

Undress AI Tool

Undress images for free

Clothoff.io

Clothoff.io

AI clothes remover

AI Hentai Generator

AI Hentai Generator

Generate AI Hentai for free.

Hot Article

R.E.P.O. Energy Crystals Explained and What They Do (Yellow Crystal)
2 weeks ago By 尊渡假赌尊渡假赌尊渡假赌
Repo: How To Revive Teammates
4 weeks ago By 尊渡假赌尊渡假赌尊渡假赌
Hello Kitty Island Adventure: How To Get Giant Seeds
3 weeks ago By 尊渡假赌尊渡假赌尊渡假赌

Hot Tools

Notepad++7.3.1

Notepad++7.3.1

Easy-to-use and free code editor

SublimeText3 Chinese version

SublimeText3 Chinese version

Chinese version, very easy to use

Zend Studio 13.0.1

Zend Studio 13.0.1

Powerful PHP integrated development environment

Dreamweaver CS6

Dreamweaver CS6

Visual web development tools

SublimeText3 Mac version

SublimeText3 Mac version

God-level code editing software (SublimeText3)

CakePHP Project Configuration CakePHP Project Configuration Sep 10, 2024 pm 05:25 PM

In this chapter, we will understand the Environment Variables, General Configuration, Database Configuration and Email Configuration in CakePHP.

PHP 8.4 Installation and Upgrade guide for Ubuntu and Debian PHP 8.4 Installation and Upgrade guide for Ubuntu and Debian Dec 24, 2024 pm 04:42 PM

PHP 8.4 brings several new features, security improvements, and performance improvements with healthy amounts of feature deprecations and removals. This guide explains how to install PHP 8.4 or upgrade to PHP 8.4 on Ubuntu, Debian, or their derivati

CakePHP Date and Time CakePHP Date and Time Sep 10, 2024 pm 05:27 PM

To work with date and time in cakephp4, we are going to make use of the available FrozenTime class.

CakePHP File upload CakePHP File upload Sep 10, 2024 pm 05:27 PM

To work on file upload we are going to use the form helper. Here, is an example for file upload.

CakePHP Routing CakePHP Routing Sep 10, 2024 pm 05:25 PM

In this chapter, we are going to learn the following topics related to routing ?

Discuss CakePHP Discuss CakePHP Sep 10, 2024 pm 05:28 PM

CakePHP is an open-source framework for PHP. It is intended to make developing, deploying and maintaining applications much easier. CakePHP is based on a MVC-like architecture that is both powerful and easy to grasp. Models, Views, and Controllers gu

How To Set Up Visual Studio Code (VS Code) for PHP Development How To Set Up Visual Studio Code (VS Code) for PHP Development Dec 20, 2024 am 11:31 AM

Visual Studio Code, also known as VS Code, is a free source code editor — or integrated development environment (IDE) — available for all major operating systems. With a large collection of extensions for many programming languages, VS Code can be c

CakePHP Creating Validators CakePHP Creating Validators Sep 10, 2024 pm 05:26 PM

Validator can be created by adding the following two lines in the controller.

See all articles