2——PHP defined函数 ill defined be defined by already defined

The

*/
 * Copyright (c) 2016，烟台大学计算机与控制工程学院
 * All rights reserved.
 * 文件名：text.cpp
 * 作者：常轩
 * 微信公众号：Worldhello
 * 完成日期：2016年5月18日
 * 版本号：V1.0
 * 问题描述：PHP
 * 程序输入：无
 * 程序输出：无
 */
<?php 
define("PI1",3.14);
$p = "PI1";
$is1 = defined($p);
$is2 = defined("PI2");
var_dump($is1);
var_dump($is2);
?>

defined() function can help us determine whether a constant has been defined. Its syntax format is:

bool defined(string constants_name

If it exists, it returns Boolean type true, otherwise it returns Boolean type false; (Note :bool indicates that the function return value type is Boolean)

The above has introduced 2-PHP defined function, including the defined content. I hope it will be helpful to friends who are interested in PHP tutorials.