Example | Name | Result |
---|---|---|
$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 . |
The reason for the two different variations of "and" and "or" operators is that they operate at different precedences. (See Operator Precedence.)
Example #1 Logical operators illustrated
<?php
// --------------------
// foo() will never get called as those operators are short-circuit
$a = (false && foo());
$b = (true || foo());
$c = (false and foo());
$d = (true or foo());
// --------------------
// "||" has a greater precedence than "or"
// The result of the expression (false || true) is assigned to $e
// Acts like: ($e = (false || true))
$e = false || true;
// The constant false is assigned to $f and then true is ignored
// Acts like: (($f = false) or true)
$f = false or true;
var_dump($e, $f);
// --------------------
// "&&" has a greater precedence than "and"
// The result of the expression (true && false) is assigned to $g
// Acts like: ($g = (true && false))
$g = true && false;
// The constant true is assigned to $h and then false is ignored
// Acts like: (($h = true) and false)
$h = true and false;
var_dump($g, $h);
?>
The above example will output something similar to:
bool(true) bool(false) bool(false) bool(true)