OOP variable scope

pspeakman

i have this file:

<?php

include_once("config.php");


echo $configvar;

  class tester{

__construct(){

   }

   public function test(){
        return $configvar ;
   }

}
?>

I need to access $configvar in test() but it isn't available, but it is in the echo, can someone explain why and what I should be doing?

Phil

niroshan

Hi pspeakman,

It failed because of the variable scope. you can over come this by simply declaring it as global inside test() function. But THIS IS HIGHLY NOT RECOMMENDED AND ITS DEPRECATED. i have mentioned it purely for your understanding..

instead what you can do is create a private property and assign the value to it and return the property.

$configvar = 'niroshan';

class tester{

private $conf;

function __construct($config){
	$this->conf = $config;
}

public function test(){	  
	return $this->conf;
}
} 

$obj = new tester($configvar);

print $obj->test();

Hope this clear for you.

Regards,
niroshan

pspeakman

Thank, that's great.

halojoy

This is how it works.
I have added some comments.

<?php

/// Setup one Class Definition
class tester{

//one class variable
public $cnf_var;

//run when 'new tester($x);'
public function __construct($submit){
	//set class variable to what was submitted
	$this->cnf_var = $submit;
}

public function test(){
	//send the class variable
    return $this->cnf_var;;
}
}
////////////////////


// test run
include_once("config.php");

// Construct a NEW objeect $obj of Class 'tester' and submit $configvar
$obj = new tester($configvar);

//echo what was returned from function test() in $obj class
echo $obj->test();


?>

If you want to learn more about Class and Object
and OOP (objeect orieented programing):
php+beginners+oop+class+tutorial
🙂

TheoGB

Of course the point to remember here is that the class member retains a copy of the variable when you pass it to the constructor and that's what you're printing out.

If you change the value of $configvar subsequent to instantiating the class, the value returned by the class method will not reflect this change.

If you need genuine 'global' variables for configuration purposes, to be read at any point in your PHP you could either use
$_SESSION['variablename']
remembering to use session_start() first, or use a database table specifically for this purpose and retrieve a value when you need it.

bradgrafelman

TheoGB;10949255 wrote:
If you need genuine 'global' variables for configuration purposes, to be read at any point in your PHP you could either use
$_SESSION['variablename']
remembering to use session_start() first, or use a database table specifically for this purpose and retrieve a value when you need it.

Stealing the $_SESSION array just to use a global variable seems like a kludge at best - why not just use the $GLOBALS array?

Then again, since global variables are deprecated, that wouldn't be too good either. Assuming that you really needed this functionality, you should either a) find some OOP tutorials, because it doesn't sound like you're fully grasping the topics, or b) use pass-by-reference instead of pass-by-value. Example:

class tester { 
  private $configvar;

  public function __construct(&$configvar) { 
    $this->configvar = &$configvar;
   } 

  public function test() { 
    echo $this->configvar . "\n"; 
  } 
}

$configvar = "Hello world!";

$obj = new tester($configvar);
$obj->test(); // outputs: Hello world!

$configvar = "Bye world!";
$obj->test(); // outputs: Bye world!

TheoGB

Global variables are only deprecated to prevent people using them all the time and promoting code that is hard to read and follow.

Passing by references in that way is reversing the point of them in my view, given the nature of PHP is to have code generated on a 'per page' basis, rather than as a single app, as you would in a standalone executable in C/C++/C#/Java. Normally you would use it to affect a complex type like another class that exists outside of a second class from within that class. The only real-world use I've found for it is in passing my Smarty class into another class' method so I can assign variables in a reusable code block.

As to the use of $SESSION vs. $GLOBALS well the $GLOBALS variables are only global in the scope of the current page (that I know of). By using $SESSION you can retain your value as a cookie while the user's viewing each page, which is really what most global variable use would tend to be about in the world of websites and PHP, surely?

bradgrafelman

TheoGB wrote:
By using $SESSION you can retain your value as a cookie while the user's viewing each page, which is really what most global variable use would tend to be about in the world of websites and PHP, surely?

Using $SESSION vs. $GLOBALS has nothing to do with variable scope and everything to do with variable persistence. Since the variable given in the example was $configvar, I assumed that the data it contained was static (e.g. what you would find in a config.php script).

TheoGB

bradgrafelman;10949394 wrote:
Using $_SESSION vs. $GLOBALS has nothing to do with variable scope and everything to do with variable persistence. Since the variable given in the example was $configvar, I assumed that the data it contained was static (e.g. what you would find in a config.php script).

Well in that case probably a DEFINE would make more sense. I just presumed there was a database read in there...

Global variables and persistence are strongly linked in PHP in my view, because we aren't using a single application with multiple views as we would in a standalone app or in a Silverlight type experience. It's one of the reasons OOP is a bit dodgy in PHP and while I use it, I don't find it helpful to adhere to the sort of strict rules I would apply to C-based languages.