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HomeBackend DevelopmentPHP TutorialThinkPHP的自定义恒量和系统常量的使用

ThinkPHP的自定义常量和系统常量的使用

常量我们都知道就是定义好一个不变的量,在php中常量的定义规则是define("常量名",“常量值”);

即在所有的页面中就就可以去使用这个常量单纯的定义几个常量没有任何意义,重要的是要去使用常量区优化代码,我所说优化代码就是提高代码的可维护性,有时候还起到简化代码的作用,但这绝对不是主要的目的。

在传统的代码书写中,我们就采用的是直接书写的方式,比如url地址等,这些东西虽然说直接去些可以去实现功能呢但是,在程序的后期维护过程中,就先得非常的困难,虽然说可以取使用替换功能,但是这不是长久之计,而且存在比这个更好的方法,就是定义常量来使用,这样的,在后期的维护中,如果是更改盘符或者变量信息,就直接修改变量就可以,虽然说道理很简单,但是能够灵活的运用却不简单。

另外除了自定义常量以外,还有一些系统常量,如果想看到这些常量信息,可以用以下的代码去实现:

// echo "

";<br>// var_dump(get_defined_constants());<br>// echo "
";

你会卡到一大串东西,里面是所有的系统常量提供你去使用,但是说明一点的是,无论是我们自定义的常量还是系统常量,比较常用的都在后面那一片,这一点是要注意的:

下面是我定义常量的一份实例代码,以think模板为例

	//定义网站域名常量	define("SET_URL","http://shop.com/");	//定义前台HOME模块的css,img。js的常量信息	define("CSS_URL",SET_URL."Public/Home/css/");	define("IMG_URL",SET_URL."Public/Home/img/");	define("JS_URL",SET_URL."Public/Home/js/");	//定义后台Admin模块的css,img。js的常量信息	define("ADMIN_CSS_URL",SET_URL."Public/Admin/css/");	define("ADMIN_IMG_URL",SET_URL."Public/Admin/img/");	define("ADMIN_JS_URL",SET_URL."Public/Admin/js/");

我们可以看到,定义常量也要有一定的技巧,一些标志性的东西要单独定义,如网站域名,还要注意常量的分组设计,做到合理有序,才能提高代码的维护性。
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