ThinkPHP cannot read system constants. Solution

ThinkPHP cannot read the system constant editing path Enhance \ Frame-ThinkPHP \ admin \ Lib \ Action \ UserAction. class. phpPHPcodepublicfunctionindex () {echo_ROOT _. '& lt; br/& g ThinkPHP cannot read system constants
Edit path: Enhance \ Frame-ThinkPHP \ admin \ Lib \ Action \ UserAction. class. php

PHP code

  Public function index () {echo _ ROOT _.'
'; Echo _ APP _;}

Access address: http: // localhost/Enhance/Frame-ThinkPHP/admin. php/user
The output content is still:
_ ROOT _
_ APP _

------ Solution --------------------
What people agree on is two Underscores. you only write one.