php logical operators

Logical Operator

Example                                                                                                                      b And (logical AND) TRUE if $a and $b are both TRUE. $a or $b Or (logical OR) TRUE, if either $a or $b is TRUE. $a xor $b Xor (logical exclusive OR) TRUE, if either $a or $b is TRUE, but not both at the same time.

! $a Not (logical not) TRUE, if $a is not TRUE.

$a && $b And (logical AND) TRUE, if $a and $b are both TRUE.

$a || $b Or (logical OR) TRUE, if either $a or $b is TRUE. ​

The reason why "AND" and "OR" have two different forms of operators is that the priorities of their operations are different (see Operator Priority).

Example #1 Logical Operator Example

<?php
// --------------------
// foo() 根本没机会被调用，被运算符“短路”了
$a = (false && foo());
$b = (true  || foo());
$c = (false and foo());
$d = (true  or  foo());
// --------------------
// "||" 比 "or" 的优先级高
// 表达式 (false || true) 的结果被赋给 $e
// 等同于：($e = (false || true))
$e = false || true;
// 常量 false 被赋给 $f，true 被忽略
// 等同于：(($f = false) or true)
$f = false or true;
var_dump($e, $f);
// --------------------
// "&&" 比 "and" 的优先级高
// 表达式 (true && false) 的结果被赋给 $g
// 等同于：($g = (true && false))
$g = true && false;
// 常量 true 被赋给 $h，false 被忽略
// 等同于：(($h = true) and false)
$h = true and false;
var_dump($g, $h);
?>

The output of the above routine is similar to:

bool(true)
bool(false)
bool(false)
bool(true)