Questions about the ^ symbol.

dr0n3

Can someone please explain to me what ^ means in PHP? I know it has something to do with xor and that it does not mean exponentiation.

Take the following code for example:

error_reporting(E_ALL ^ E_NOTICE);

This code means to display all errors, except E_NOTICE messages. How does it work though? Where else can I use ^ ?

LordShryku

As far as php is concerned, it's Xor.
http://www.php.net/manual/en/language.operators.bitwise.php

dr0n3

Okay, now does anyone mind explaining Xor in layman's terms and more specifically, how it works in error_reporting(E_ALL ^ E_NOTICE);?

tekky

$a and $b And TRUE if both $a and $b are TRUE.
$a or $b Or TRUE if either $a or $b is TRUE.
$a xor $b Xor TRUE if either $a or $b is TRUE, but not both.
! $a Not TRUE if $a is not TRUE.
$a && $b And TRUE if both $a and $b are TRUE.
$a || $b Or TRUE if either $a or $b is TRUE.

from http://www.php.net/manual/en/language.operators.logical.php

as to how it pertains in Error_reporting.... I would assume it would be something like this...

Report all errors UNLESS its in the NOTICE class...
ALL and NOTICE == ignore it
ALL but not NOTICE == show it
(since you cant have a NOT all but NOTICE... well ill skip that one) :p

[edit -- and yes... I do realize how redundant and crappy of an explanation I gave... :evilgrin: I'm tired... --]

dr0n3

TRUE if either $a or $b is TRUE, but not both.

E_ALL stands for all errors and warnings, as supported, except of level E_STRICT.

So, error_reporting(E_ALL ^ E_NOTICE) will return FALSE if E_NOTICE is TRUE, because E_ALL includes all E_NOTICE level messages. So, if E_ALL and E_NOTICE are TRUE, the result is FALSE.

If both E_ALL and E_NOTICE are TRUE, then the result will be FALSE, and no errors will be printed.

Edit: Okay, I added it all up 😃

tekky

Originally posted by dr0n3
Now, what I can’t understand is if both E_ALL and E_NOTICE are TRUE, then the result will be FALSE, and no errors will be printed. So why is this NOT the case? Or am I off the track completely?

thats right... E_ALL and E_NOTICE would be false because you want to display ALL except NOTICE

XOR truths are
a=0 b=0 = 0
a=1 b=0 = 1
a=1 b=1 = 0
a=0 b=1 = 1

(0451 in the mornin so i may have messed the 0 0 one up...)

dr0n3

Great, I understand it now. Appears I wasn't thinking straight 😛