Using $GLOBALS[] variable in PHP class function

Question

I'm trying to assign $GLOBALS['a'] variable in function from class, but haven't succeeded.

Here is my code:

<?php

 $GLOBALS['a'] = "alter";

 class db_data 
 {
   public $a;

   function __construct()
   {
     $this->a = $GLOBALS['a']; 
   }

 }

 $db = new db_data;

 echo $db->$a;

?>

And produced this error:

Notice: Undefined property: db_data::$alter.....

I tried to search on SO for this, but all questions were different and it did not resolve my problem.

stop using globals or stop using class, by using one you negate the benefit of the other. — Orangepill
– Orangepill, Commented Jun 14, 2013 at 18:34
((( always same error - syntax/inattention. Thanks a lot! )) — aleXela
– aleXela, Commented Jun 14, 2013 at 18:35

terite · Accepted Answer · 2013-06-14 19:26:08Z

2

Answers are in the question comments, but here's why it's happening

You're accidentally using the variable variables feature of PHP. When you call $thing->$a, you're actually getting the value of $a (which defined by the $GLOBALS['a'] = "alter"; line), and then getting the property of $thing with that value.

As stated in your comments, you should simply echo $db->a, as that's how PHP properties are accessed

Also, Watch out!, if the value of $a is changed elsewhere in the global scope, your db_data class will reflect that change, which you probably don't want.

edited Jun 14, 2013 at 19:26

answered Jun 14, 2013 at 18:46

terite

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3 Comments

aleXela Over a year ago

Thanks, For watch out - thats exactly what i need. if it changes, i want to use it.

aleXela Over a year ago

another thing if i'm asking - what difference between -> and :: ?

terite Over a year ago

The double colon, called the Scope Resolution Operator, is for referencing static properties or methods on a class. Basically, a static method/property is just attached to a class, rather than in instance of that class. In my opinion, the error message should show -> instead of ::, but it's PHP.

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