ThinkPHP template judgment output Defined tag usage detailed explanation_PHP tutorial

The defined tag of the ThinkPHP template engine is used to determine whether the constant has been defined .
ThinkPHP's defined tag is used to determine whether a constant has been defined. Its function is equivalent to the defined() function in PHP. The defined tag is used as follows:

<present name="常量">要输出的内容</present>

First define a constant in the module operation (such as: Index/display) and output the template:

define("SITE_NAME", "脚本之家");
$this->display();

Use the defined tag in template/Tpl/default/Index/display.html as follows:

<defined name="SITE_NAME">网站名称：{*SITE_NAME}</defined>

Running this example will output:

网站名称：脚本之家

The equivalent PHP code for this example is as follows:

<?php
if(defined("SITE_NAME")){
  echo '网站名称：',constant("SITE_NAME");
}
?>

If the judgment is not defined, you can use:

<notdefined name="SITE_NAME">{*SITE_NAME}不存在活未定义</notdefined>

The above two examples are combined as follows:

<defined name="SITE_NAME">网站名称：{*SITE_NAME}<else/>{*SITE_NAME}不存在活未定义</defined>

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