Logical Operators, || or OR?

I remember reading a while back in regards to logical operators that in the case of OR, using || was better than or (or vice versa).

I just had to use this in my project when it came back to me but I can't remember which operator was recommended or if it was even true.

Which is better and why?

标签： php operators logical-operators or-operator

8条回答

Anthone

2楼-- · 2019-01-02 23:43

The difference between respectively || and OR and && and AND is operator precedence :

`$bool = FALSE || TRUE;`

interpreted as ($bool = (FALSE || TRUE))
value of $bool is TRUE

`$bool = FALSE OR TRUE;`

interpreted as (($bool = FALSE) OR TRUE)
value of $bool is FALSE

`$bool = TRUE && FALSE;`

interpreted as ($bool = (TRUE && FALSE))
value of $bool is FALSE

`$bool = TRUE AND FALSE;`

interpreted as (($bool = TRUE) AND FALSE)
value of $bool is TRUE

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Melony?

3楼-- · 2019-01-02 23:49

There is no "better" but the more common one is ||. They have different precedence and || would work like one would expect normally.

See also: Logical operators (the following example is taken from there):

// 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;

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\"骚年 ilove

4楼-- · 2019-01-02 23:52

I know it's an old topic but still. I've just met the problem in the code I am debugging at work and maybe somebody may have similar issue...

Let's say the code looks like this:

$positions = $this->positions() || [];

You would expect (as you are used to from e.g. javascript) that when $this->positions() returns false or null, $positions is empty array. But it isn't. The value is TRUE or FALSE depends on what $this->positions() returns.

If you need to get value of $this->positions() or empty array, you have to use:

$positions = $this->positions() or [];

EDIT:

The above example doesn't work as intended but the truth is that || and or is not the same... Try this:

<?php

function returnEmpty()
{
  //return "string";
  //return [1];
  return null;
}

$first = returnEmpty() || [];
$second = returnEmpty() or [];
$third = returnEmpty() ?: [];

var_dump($first);
var_dump($second);
var_dump($third);
echo "\n";

This is the result:

bool(false)
NULL
array(0) {
}

So, actually the third option ?: is the correct solution when you want to set returned value or empty array.

$positions = $this->positions() ?: [];

Tested with PHP 7.2.1

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Bombasti

5楼-- · 2019-01-02 23:55

They are used for different purposes and in fact have different operator precedences. The && and || operators are intended for Boolean conditions, whereas and and or are intended for control flow.

For example, the following is a Boolean condition:

if ($foo == $bar && $baz != $quxx) {

This differs from control flow:

doSomething() or die();

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Deceive 欺骗

6楼-- · 2019-01-02 23:57

Source : http://bit.ly/1hxDmVR

Here is sample code for working with logical operators:

<html>

<head>
<title>Logical</title>
</head>
<body>
<?php
$a=10;
$b=20;
if($a>$b)
{
    echo " A is Greater";
}
elseif($a<$b)
{
    echo " A is lesser";
}
else
{
     echo "A and B are equal";
}
?>
<?php
    $c=30;
    $d=40;
   //if(($a<$c)AND($b<$d))
   if(($a<$c)&&($b<$d))
   {
       echo "A and B are larger";
   }
   if(isset($d))
       $d=100;
   echo $d;
   unset($d);
?>
<?php
    $var1=2;
    switch($var1)
    {
        case 1:echo "var1 is 1";
               break;
        case 2:echo "var1 is 2";
               break;
        case 3:echo "var1 is 3";
               break;
        default:echo "var1 is unknown";
    }
?>
</body>
</html>

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SAY GOODBYE

7楼-- · 2019-01-02 23:59

There is nothing bad or better, It just depends on the precedence of operators. Since || has higher precedence than or, so || is mostly used.

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