Logical Operators

Domains:
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 before the "or" operation occurs
// 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 before the "and" operation occurs
// 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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