[prev in list] [next in list] [prev in thread] [next in thread] 

List:       php-general
Subject:    Re: [PHP] Re: tutorial on global variables
From:       Philip Olson <philip () cornado ! com>
Date:       2002-05-02 19:44:59
[Download RAW message or body]

An issue/confusion of register_globals, global, and
variable scope exists out there; here are some thoughts:

 a) As of PHP 4.2.0, register_globals defaults to off.

    This is a major change to consider.
    register_globals is a PHP directive that lives in
    php.ini, the configuration file that controls PHP.

    http://www.php.net/release_4_2_0.php
    http://uk.php.net/manual/en/security.registerglobals.php

    Different server setups have different settings,
    so not relying on register_globals = on will make
    your scripts more portable.

 b) register_globals looks/sounds like global when
    really they are very different topics.

    http://us.php.net/manual/en/configuration.php#ini.register-globals
    http://www.php.net/manual/en/language.variables.scope.php

    register_globals will create $a from example.com/foo.php?a=apple
    while when register_globals = off, $a will NOT exist.
    One can always use $HTTP_GET_VARS or $_GET for this like so:

      print $_GET['a'];

    Use of import_request_variables() or extract() to act in a
    similar fashion as register_globals is possible too.

    http://fr2.php.net/import_request_variables
    http://ca.php.net/extract

 c) As of PHP 4.1.0, super/auto global arrays became available.

    The new predefined PHP variables such as $_POST, $_GET,
    $_SERVER are identical to their existing counterparts of
    $HTTP_POST_VARS, $HTTP_GET_VARS, etc. except that:

    1) The new autoglobal arrays are automagically global
       while their sibling arrays ($HTTP_*_VARS) are not.
         http://www.php.net/manual/en/reserved.variables.php
    2) Shorter is better :)
    3) They are different variables, $_GET is not a reference
       to $HTTP_GET_VARS but rather they are two seperate
       copies, same information.
         http://fr2.php.net/release_4_1_0.php

    The manual discusses all the superglobals, others are 
    $_REQUEST, $_FILES and $_SESSION.

Being that this is all relativly new, PHP is in sort
of a mild transitional state.  The above announcements
explain why.  People just starting out with PHP have
slightly more homework to do than before.  But, these
same people have less chance for security mistakes now.

And it's worth noting, register_globals does affect
predefined SERVER variables too.  So when off the
variables $DOCUMENT_ROOT, $PHP_SELF, etc. will NOT
exist.  Go through $_SERVER or $HTTP_SERVER_VARS instead.
This is something to consider when writing "portable"
scripts (or hacking non-portable scripts to work).  A 
possible usage is:

  // if register_globals is off, create server vars
  if (!ini_get('register_globals')) {
    extract($HTTP_SERVER_VARS);
    print 'we just created $REMOTE_ADDR because register_globals is off';
    print "\nREMOTE_ADDR: $REMOTE_ADDR";
  } else {
    print 'register_globals is on so $DOCUMENT_ROOT et al already exists';
    print "\nDOCUMENT_ROOT: $DOCUMENT_ROOT";
  }

Phew, hope that helps :)

Regards,
Philip Olson


-- 
PHP General Mailing List (http://www.php.net/)
To unsubscribe, visit: http://www.php.net/unsub.php

[prev in list] [next in list] [prev in thread] [next in thread]