DEFINED标签用于判断某个常量是否有定义，用法如下： <defined name="NAME"> NAME常量已经定义 </defined> <defined name="NAME"> NAME常量已经定义 </defined> name属性的值要注意严格大小写如果判断没有被定义，可以使用： <notdefined name="NAME"> NAME常量未定义 </notdefined> <notdefined name="NAME"> NAME常量未定义 </notdefined> 可以把上面两个标签合并成为： <defined name="NAME"> NAME常量已经定义 <else /> NAME常量未定义 </defined> <defined name="NAME"> NAME常量已经定义 <else /> NAME常量未定义 </defined> <div class="view-foot"> <div class="article-jump"> <span style="display: block;" class="jump-up">上一篇：<a href="/manual/thinkphp /1813" data-articleid="1813">Empty标签</a></span> <span class="jump-down">下一篇：<a href="/manual/thinkphp/1815" data-articlei d="1815">Assign标签</a></span> </div> <a class="view-backtop"><i class="icon-arrow-up2"></i></a> </div> </div> <div class="view-foot"> <div class="article-jump"> <span style="display: block;" class="jump-up">上一篇：<a href="/manual/thinkphp /1813" data-articleid="1813">Empty标签</a></span> <span class="jump-down">下一篇：<a href="/manual/thinkphp/1815" data-articlei d="1815">Assign标签</a></span> </div> <a class="view-backtop"><i class="icon-arrow-up2"></i></a> </div> </div>