Posted by Simon Bridgewater on 07/08/05 21:37

& is bitwise

$a= 9;
$b =9;
$c = 6;

$a & $b = 9;
$a & $c = 0;


&& is a logical and

$a && $b =1
$a && $c = 0;



"Tom Thackrey" <use.signature@nospam.com> wrote in message
news:0czze.3199$6%2.1520@newssvr21.news.prodigy.com...
>
> On 8-Jul-2005, "Michael B. Trausch" <fdZEROman+spam@gmail.nospam.com>
> wrote:
>
> > I have a question regarding bitwise operators, I've been trying to
> > figure this out for about two days now, and I just can't seem to get it.
> > What I'm trying to do is use a variable to hold a bitmask of 'flags'
> > for users on a website. The function below is supposed to be a search
> > function for one of those flags in a particular thing.
> >
> > The idea is that when something calls userId(), it should get to see
> > what type of user flags that are supported. Now I've moved things
> > around, and it seems like the only if that ever executes is the first
> > one, the code doesn't ever reach any of the elseif blocks.
> >
> > I want the function to search for the first user that it finds has a bit
> > set in the bitmask and return the userId as supplied by the cookie that
> > represents that bitmask.
> >
> > Optionally, userId() can be called with one of the arguments specifying
> > a particular usertype to look for that particular usertype. The user
> > can be logged into multiple sections of the site at a time, so if
> > they're entering something where they need the USER_ADMIN privilege, I
> > should be able to call userId(USER_ADMIN) and get their UID if they're
> > an admin and E_NOT_LOGGED_IN if they're not logged in as an admin. Same
> > goes for any of the options that are defined. Can anyone else see what
> > is wrong with this?
> >
> > Thanks for the help in advance.
> >
> >
> > Constants defined for USER_*:
> > =============================
> >
> > define('USER_NOBODY', 0x00000000);
> > define('USER_SEEKER', 0x00000001);
> > define('USER_MEMPL', 0x00000002);
> > define('USER_SEMPL', 0x00000004);
> > define('USER_ADMIN', 0x00000008);
> > define('USER_ANYBODY', 0xffffffff);
> >
> > Code that isn't working:
> > ========================
> >
> > function userId($pref = USER_ANYBODY)
> > {
> > /*
> > * If the user is logged in, this will return their user ID.
> > * If they are not, then it won't. If more then one user is
> > * logged in, this function will prefer MEMPL and SEMPL types
> > * over any other, unless specified by $pref.
> > */
> >
> > $uT = userType();
> >
> > if(userAccess($uT, $pref))
> > {
> > /*
> > * The usertype that we're looking for is logged in.
> > */
> >
> > if(($pref & USER_SEEKER) > 0)
> > {
> > $tmpCookie = $_COOKIE['seeker'];
> > list($id, $i, $i, $i, $i, $i, $i) = explode(':',
$tmpCookie);
> >
> > return($id);
> > }
> >
> > elseif(($pref & USER_MEMPL) > 0)
> > {
> > $tmpCookie = $_COOKIE['mEmpl'];
> > list($id, $i, $i, $i, $i, $i, $i) = explode(':',
$tmpCookie);
> >
> > return($id);
> > }
> >
> > elseif(($pref & USER_SEMPL) > 0)
> > {
> > $tmpCookie = $_COOKIE['sEmpl'];
> > list($id, $i, $i, $i, $i, $i, $i) = explode(':',
$tmpCookie);
> >
> > return($id);
> > }
> >
> > elseif(($pref & USER_ADMIN) > 0)
> > {
> > $tmpCookie = $_COOKIE['admin'];
> > list($id, $i, $i, $i, $i, $i, $i) = explode(':',
$tmpCookie);
> >
> > return($id);
> > }
> > }
> >
> > // Oops. We don't have anything to do, return E_NOT_LOGGED_IN.
> >
> > return(E_NOT_LOGGED_IN);
> > }
>
> The problem is you aren't using the bitwise operators. & is not bitwise,
&&
> is
>
> Also, you don't need the >0, if ($pref && USER_ADMIN) will work just fine
> and won't have a problem if you use the high order bit as a flag.
>
> --
> Tom Thackrey
> www.creative-light.com
> tom (at) creative (dash) light (dot) com
> do NOT send email to jamesbutler@willglen.net (it's reserved for spammers)

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