[Resolved] Understanding OOP

[faux_trot]

Greetings,
I'm currently working on a project to help myslef understand the rules and syntax of PHP (php4 for now) OOP.

To arrive at the point, I've got two files, each containing a class. One class defines my database, and the other defines my session/user functions. It looks something like this:

<?php
/*********************
Session Management 2
**********************/
include("db.php");  

//creating an instance of my db handlng class
$database = new DB;


class Session {

   var $username; 
   var $password;
   var $ctime;

   function Session () {
   		$this->ctime = time();	
		$this->startSession();
		//$database = new DB; -this didn't work
		}

   function isOnline() {
   	  if(isset($_SESSION['username'])){
	   	  $username = $_SESSION['username'];
		  $pre_q = "SELECT * from ".TBL_ACTIVE_USERS." where username = '$username'";
		  $checkOnline = mysql_query($pre_q, $database->connection);
	      if (mysql_num_rows($checkOnline) != 0) {
		      return true;  // is online...
		      } 
	      }

  else {
	  return false;  // is not online... 
	  }
	}	

function startSession() {
	session_start();
	$navigator_user_agent = strtolower( $_SERVER['HTTP_USER_AGENT'] );
	if (stristr($navigator_user_agent, "msie")) header("Cache-control: private");  //ya msie fix 
	$this->setSessionVars();
	}

function setSessionVars() {
	$_SESSION['ip'] = $_SERVER['REMOTE_ADDR'];
	if ($this->isOnline()) {
		$_SESSION['timestamp'] = $this->ctime;
	 	$_SESSION['userip'] = $_SERVER['REMOTE_ADDR'];
	 	$database->updateActiveUser($_SESSION['username'], $_SESSION['timestamp'], $_SERVER['PHP_SELF']);
		}
	else {
		 $_SESSION['timestamp'] = $this->ctime;
	 	 $_SESSION['sessionlevel'] = GUEST_LEVEL; // sets guest level access
	 	 $_SESSION['sessionuser'] = GUEST_NAME; //sets guests level name
	 	 $database->updateActiveGuest($_SESSION['ip'], $_SESSION['timestamp'], SID, $_SERVER['PHP_SELF']);//please**note** this line
	 	 }
	}
//more code after this

I'm getting an error when I call this function from the database. I know I'm probably doing something very wrong, and I'm open to input.

I suppose my main issue is this... I'm getting a Fatal error: Call to a member function on a non-object at about this line. (see "note")

Thank you for your kind consideration of my code
🙂

Edit: I hope I'm posting this in the correct forum. I haven't been using php that long (or any programming language for that matter) and just assumed this is where I should post.

[planetsim]

Ok well $database isnt defined in the scope of the class. Basically if you wish to use the defined $database within your class you will need to either send it as an argument or use

global $database; 

To this class $database firstly doesnt exist in any of the methods as a variable and to PHP isnt defined within the scope of the class as an object.

[faux_trot]

I don't think thats going to help ps. I tried defining it globally, and it didn't help.

Here's a little more info, now that I have a bit more time to type this out

db.php is my database class with an include to con.php. con.php provides constants, making the code a little bit more modular. no classes here though

db.php contains all the query strings and handlers ($this->connection which is my link id and functions to populate / and tidy up my SQL tables based on user sessions.)

sm.php is the session management page. It starts session and assigns various session variables for the particular session.

I almost think of it like this. All my base functionality is built into the db.php file. sm.php decisions on what db.php would do without making a logic check. It breaks the two programs into base functionality and control. however, how is one supposed to call a function from another class. I'm not sure what I should do.

There was one intersting thing that I noticed. the "scope resolution operator" "::" I don't know exactly how this works yet and I'm trying to grasp the concept. However, if I use it, I don't get Fatal error for my class object call, but I don't know if its calling the function in the same way that the -> operator does (or if it is significanly different that it would change the function's functionality 😕 .

Thanks for the input though... Maybe I should take this concept back to the notepad and make it flow differently?

[Shrike]

planetsim is telling you that the instance of the database class ($database) is in the global scope, and not available with in the method setSessionVars(). You would need to use

global $database;

in that method.

Alternatively add the $database as a class variable, and refer to it as $this->database, e.g.

class Session { 
  ...
  var $database;
  ...

  function Session () { 
    ...
    $this->database = new DB;
    ...
  }
  function setSessionVars(){
    ...
    $this->database->updateActiveGuest(...)
    ...
  }
}

The :: operator is used to refer to classes and their methods statically, for example when chaining parent constructors

class A extends B
{
  function a()
  {
    parent::b();
  }
}
class B
{
  function b()
  {
    //do Something Fun
  }
}

[faux_trot]

Thank you, and thanks to planet sim. I'm a little dense, and hearing your explination makes a lot of sense, Shrike.

I wasn't really aware of using it as a class variable. I've only seen that done once or twice, and I didn't really find good documentation.

Thanks for the swift attention to my post ps and shrike. I'll post tomorrow on my progress.

P.S. thanks to site admin for this resource.

[faux_trot]

Ok Current update:

It still throws the same error. I've attached the two files. (Just to make sure its not something that I'm just completely screwing up which is probably the case.
🙁 (its rough being a newbie eh?)

From what you guys have been saying, I have a sinking feeling that it might be the version of php my host is running: suPHP. (they allow for a local config file) Would there be a setting in my php.ini file that would prevent me from being able to call class functions from another class?

[Shrike]

You are calling $this->database->updateActiveUser()/updateActiveGuest() in setSessionVars() and this->database->checkOnlineDB in isOnline() before you have created the database object in the constructor. Try:

function Session () {
  $this->database = new DB;
  $this->ctime = time();	
  $this->startSession();
}

I am curious as to where you are instantiating the Session class. Usually you would call the Session class methods from there rather than in the constructor itself.

[faux_trot]

Its funny when its something that easy, thanks Shrike 🙂

Currently I'm calling it from a test file. I pass some variables to a function using an instance of session called in the same file.

eventually I plan to call it from my header file and a process file. When a user tries to access a page that they don't have proper level for (i.e. if($_SESSION['userlevel'] < $requred_level /defined in page / ) redirect to login page(); else display log out button(); )

again, this is probably more work than my poor server should have to handle, but its mostly for my own education.