note 18879 deleted from language.oop by vincent
| From: | vincent@php.net | Date: | Thu, 11 Sep 2003 19:58:48 +0000 |
| Subject: | note 18879 deleted from language.oop by vincent | ||
| References: | 1 | Groups: | php.notes |
| Request: | Send a blank email to php-notes+get-56200@lists.php.net to get a copy of this message | ||
Note Submitter: php@priorwebsites.com
----
If your new to PHP classes, beware of the scope of variables.
In particular, if a variable is defined as an implicitly static variable for the class as a whole,
make sure you use the $this->my_var syntax, not just $my_var.
First, using the scope WRONGLY:
class my_wrong_class
{
/* A general class variable */
$db_link;
/* A constructor function for the class */
function my_class()
{
/* this will give the $db_link variable a value */
/* but only as a local variable in this function. */
$db_link = mysql_connect('localhost','root','');
}
function do_something()
{
$query = "SELECT * FROM my_table";
/* Again, the $db_link reference is wrong! Won't work */
$result = mysql_query( $query, $db_link );
}
}
Now doing the scope CORRECTLY:
class my_right_class
{
/* A general class variable */
$db_link;
/* A constructor function for the class */
function my_class()
{
/* Ah! Correctly references the class variable */
$this->db_link = mysql_connect('localhost','root','');
}
function do_something()
{
$query = "SELECT * FROM my_table";
/* Ah! Correctly uses the class variable */
$result = mysql_query( $query, $this->db_link );
}
}
If you are a seasonsed PHP programmer you may say nobody would do that. I as a seasoned non-PHP
programmer did, couldn't understand why my code didn't work, and fudged it, till now...