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Logical Operators

Logical Operators
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)

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