如何正确理解PHP include作用域_PHP教程

2016-07-15 13:34 910浏览原创

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><span> ?php  </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>

<ol class="dp-xml"><li class="alt"><span><span class="tag"><</span><span> ?php  </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>

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><span> ?php  </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><span class="tag-name">br</span><span> </span><span class="tag">/></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><span class="tag-name">br</span><span class="tag">/></span><span>';  </span></li><li class="alt"><span>}  </span></li><li><span class="tag">?></span><span> </span></li></ol>

<ol class="dp-xml"><li class="alt"><span><span class="tag"><</span><span> ?php  </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>

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