⌂ Home ▲ Previous: Arithmetic operators ▼ Next: Bitwise 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: Logical operators
<?php
$a = true; $b = false;
// Logical conjunction (with high precedence)
$c = $a && $b;
print("{$a} && {$b} = {$c}\n");
$c = $a && $a;
print("{$a} && {$a} = {$c}\n");
$c = $b && $b;
print("{$b} && {$b} = {$c}\n\n");
// Logical disjunction (alternation) (with high precedence)
$c = $a || $b;
print("{$a} || {$b} = {$c}\n");
$c = $a || $a;
print("{$a} || {$a} = {$c}\n");
$c = $b || $b;
print("{$b} || {$b} = {$c}\n\n");
// Logical negation (with high precedence)
$c = !$a;
print("!{$a} = {$c}\n");
$c = !$b;
print("!{$b} = {$c}\n\n");
// Logical conjunction (with low precedence)
$c = ($a and $b);
print("({$a} and {$b}) = {$c}\n");
$c = ($a and $a);
print("({$a} and {$a}) = {$c}\n");
$c = ($b and $b);
print("({$b} and {$b}) = {$c}\n\n");
// Logical disjunction (alternation) (with low precedence)
$c = ($a or $b);
print("({$a} or {$b}) = {$c}\n");
$c = ($a or $a);
print("({$a} or {$a}) = {$c}\n");
$c = ($b or $b);
print("({$b} or {$b}) = {$c}\n\n");
// Exclusive disjunction (alternation) (with low precedence)
$c = ($a xor $b);
print("({$a} xor {$b}) = {$c}\n");
$c = ($a xor $a);
print("({$a} xor {$a}) = {$c}\n");
$c = ($b xor $b);
print("({$b} xor {$b}) = {$c}\n\n");
View: Example
Execute:
Result:
1 && =
1 && 1 = 1
&& =
1 || = 1
1 || 1 = 1
|| =
!1 =
! = 1
(1 and ) =
(1 and 1) = 1
( and ) =
(1 or ) = 1
(1 or 1) = 1
( or ) =
(1 xor ) = 1
(1 xor 1) =
( xor ) =
Example: 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)
▵ Up ⌂ Home ▲ Previous: Arithmetic operators ▼ Next: Bitwise operators