Double Dollar Sign

Keep seeing weird stuff in the OsCommerce code...

What is a double dollar sign variable? A G search doesn't show any relevant results whatsoever and before I go fix these 'typo's' I need to know whether they are just typo's or not.

Example:

<?php
  if (isset($$payment->form_action_url)) {
    $form_action_url = $$payment->form_action_url; //see the $$ ?!  :confused: 
  } else {
    $form_action_url = tep_href_link(FILENAME_CHECKOUT_PROCESS, '', 'SSL');
  }

  echo tep_draw_form('checkout_confirmation', $form_action_url, 'post');

  if (is_array($payment_modules->modules)) {
    echo $payment_modules->process_button();
  }

  echo tep_image_submit('button_confirm_order.gif', IMAGE_BUTTON_CONFIRM_ORDER) . '</form>' . "\n";
?>

PHP:

I need to get into this OO stuff and advanced 'beyond the Bible' coding.

-> and => is all new to me as well. Any one know a good intro to this type of coding?

 

php.net has all the best information. Read the comments as well as the documentation.

 

Sarah, exactly what my problem was.

I'm on php.net all day every day just for reference. I'd consider myself a medium to advanced PHP nerd, well... at least 3 years ago. Now I picked up on it again it seems to have moved on a LOT!

I searched on Google for all obvious combo's like 'double dollar sign variable php' etc. Google doesn't really like searches with characters like $ so that didn't get me far either.

The PHP Bible and another few books got me where I am now but it seems I could do with a next millennium programming style PHP book. If anyone can recommend a good one that covers stuff like the variable variables and -> and => etc. I'd be glad to hear about it.

Have to do some serious OsCommerce hacking so would be handy to get up to spec so I'll be able to contribute standardized re-usable code as well.

 

heh nice... variable variable.... never have had to use it yet myself but you never know... .... what kind of module are you making for oscommerce? i have been modifying & hacking oscommerce for 2 years now and zen cart since its release. the hardest part for me is going from structural to object oriented programming... i still have some problem with it other than the easy stuff...

on my things to do list:
-code an application base
-get working on my librairy of php classes

good luck...

 

I just released my first contribution (ePDQ Barclays UK Payment Module) and this rewarding feeling I have must be what Opens Source is all about. Even when I realize it's ugly code (mainly because of previous code already there). I didn;t have the time to make it as good as I would have wanted bu people were desparate so I sort of prematurely released it nonetheless.

The OO stuff is still bugging me too. I'm getting the hang of reading it now but writing it is a different story. Things like Variable Variables might be handy but certainly don't make it easier to read.

I've written 10K+ lines of PHP before but all old school 'structural' if that's what you call it.

I have to say, turning OsC is such a relief when you've been bound to limited 3d party stuff. Loads and tonnes and piles of stuff I still ahve in the back of my mind, ready to start coding on to make it even better.

 

Variable variables are great for assigning key=value in an associative array. i.e.:

for(reset($_POST); $key = key($_POST); next($_POST)) {
  $$key = $_POST[$key];
}

Code (markup):

 

Wow... it is as if you were speaking Chinese to me... I really need to learn PHP

BUt, believe it or not, there aren't any schools to learn that here! All you can get are some crappy lessons of very basic html, and after that they give you a diploma with "webmaster" on it

 

There wasn't any such thing as HTML when I was going to school. Aa a matter of fact, even BASIC was still just a gleam in Bill Gates' eye when I graduated from H.S.

 

He he... I remember learning basic when I was a kid...

I am now reading a book about PHP. Of course, it takes me half an hour to understand one page... and I still have another 880 to go

 

I think just about everybody "cut their teeth" with BASIC..

As far as learning PHP, I think your best bet would be to practice the code as you read the book. If you're anything like me, reading techie stuff puts me right to sleep. Plus, I never really get what is being said until I use it and play with it.

And not to overwhelm you, but if you're using PHP to create websites, look into Smarty Templates. They will help you to develop good programming practices, i.e. keeping your PHP functions seperate from your HTML.

 

i.e. evaluate from left to right
there is no operator called $$ in php

simple way is rewrite $$$var to ${${$var}} and you will be able to understand better.

you can have $$$var or $$$$$var etc...

as long as evaluation of each $ from left to right results in a defined variable.

So there is no reference etc, its just a plain left to right token evaluation in php grammar.

Some guy had asked my friend the same question in interview and then explained him that it is reference to reference, which is completely wrong. It has nothing to do with reference.
It's simple php grammar:
evaluate anything after $ (with in same side of another operator) and treat $(evaluated value) as variable, and look up the symbol table.

for e.g.
$var1 = 'dog';
$$$var1 = 'bark';
would give you:
PHP Notice: Undefined variable: dog
(i.e. it didn't find $dog)
$$$var is evaluated as ${${$var1}} and in each step php will try to find the variable in symbol table or will create one if there is an assignment operation immediately.

another example is:

${'hello' . 'world'} = 'monkeyman';
echo $helloworld

other example is this:
$var1 = 'dog cat';
$$var1 = 'bark';
echo $dog; //undefined
echo ${'dog cat'}; //prints bark