PHP 7.4.0 alpha 3 Released

Operadores

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Um operador é algo que recebe um ou mais valores (ou expressões, no jargão de programação) e que devolve outro valor (e por isso os próprios construtores se tormam expressões).

Operadores podem ser agrupados segundo o número de valores que aceitam. Operadores unários recebem um único valor, por exemplo ! (o operador lógico de negação) ou ++ (o operador de incremento). Operadores binários aceitam dois valores, como os operadores aritméticos + (soma) e - (subtração), além da maioria dos operadores PHP dessa categoria. Finalmente há um único operador ternário, ? :, que aceita três valores; normalmente conhecido simplesmente como "o operador ternário" (embora um nome melhor fosse operador condicional).

A lista completa dos operadores no PHP está na seção sobre Precedência de Operadores. Essa seção também explica precedência e combinações, que governam exatamente como expressões contendo vários operadores são avaliados.

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User Contributed Notes 8 notes

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208
Anonymous
15 years ago
of course this should be clear, but i think it has to be mentioned espacially:

AND is not the same like &&

for example:

<?php $a && $b || $c; ?>
is not the same like
<?php $a AND $b || $c; ?>

the first thing is
(a and b) or c

the second
a and (b or c)

'cause || has got a higher priority than and, but less than &&

of course, using always [ && and || ] or [ AND and OR ] would be okay, but than you should at least respect the following:

<?php $a = $b && $c; ?>
<?php $a
= $b AND $c; ?>

the first code will set $a to the result of the comparison $b with $c, both have to be true, while the second code line will set $a like $b and THAN - after that - compare the success of this with the value of $c

maybe usefull for some tricky coding and helpfull to prevent bugs :D

greetz, Warhog
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25
yasuo_ohgaki at hotmail dot com
18 years ago
Other Language books' operator precedence section usually include "(" and ")" - with exception of a Perl book that I have. (In PHP "{" and "}" should also be considered also). However, PHP Manual is not listed "(" and ")" in precedence list. It looks like "(" and ")" has higher precedence as it should be.

Note: If you write following code, you would need "()" to get expected value.

<?php
$bar
= true;
$str = "TEST". ($bar ? 'true' : 'false') ."TEST";
?>

Without "(" and ")" you will get only "true" in $str.
(PHP4.0.4pl1/Apache DSO/Linux, PHP4.0.5RC1/Apache DSO/W2K Server)
It's due to precedence, probably.
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1
ivijan dot stefan at gmail dot com
4 days ago
If you use "AND" and "OR", you'll eventually get tripped up by something like this:

<?php
$this_one
= true;
$that = false;
$truthiness = $this_one and $that;
?>

Want to guess what $truthiness equals?

If you said "false"  ...it's wrong!

"$truthiness" above has the value "true". Why?  "=" has a higher precedence than "and". The addition of parentheses to show the implicit order makes this clearer:

<?php
($truthiness = $this_one) and $that;
?>

If you used "&&" instead of and in the first code example, it would work as expected and be "false".

This also works to get the correct value, as parentheses have higher precedence than "=":

<?php
$truthiness
= ($this_one and $that);
?>
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3
figroc at gmail dot com
10 years ago
The variable symbol '$' should be considered as the highest-precedence operator, so that the variable variables such as $$a[0] won't confuse the parser.  [http://www.php.net/manual/en/language.variables.variable.php]
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-6
phpnet dot 20 dot dpnsubs at xoxy dot net
11 years ago
Note that in php the ternary operator ?: has a left associativity unlike in C and C++ where it has right associativity.

You cannot write code like this (as you may have accustomed to in C/C++):

<?php
$a
= 2;
echo (
   
$a == 1 ? 'one' :
   
$a == 2 ? 'two' :
   
$a == 3 ? 'three' :
   
$a == 4 ? 'four' : 'other');
echo
"\n";
// prints 'four'
?>

You need to add brackets to get the results you want:

<?php
$a
= 2;

echo (
$a == 1 ? 'one' :
        (
$a == 2 ? 'two' :
        (
$a == 3 ? 'three' :
        (
$a == 4 ? 'four' : 'other') ) ) );
echo
"\n";
//prints 'two'
?>
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-34
me at robrosenbaum dot com
12 years ago
The scope resolution operator ::, which is missing from the list above, has higher precedence than [], and lower precedence than 'new'. This means that self::$array[$var] works as expected.
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-37
rick at nomorespam dot fourfront dot ltd dot uk
13 years ago
A quick note to any C developers out there, assignment expressions are not interpreted as you may expect - take the following code ;-

<?php
$a
=array(1,2,3);
$b=array(4,5,6);
$c=1;

$a[$c++]=$b[$c++];

print_r( $a ) ;
?>

This will output;-
Array ( [0] => 1 [1] => 6 [2] => 3 )
as if the code said;-
$a[1]=$b[2];

Under a C compiler the result is;-
Array ( [0] => 1 [1] => 5 [2] => 3 )
as if the code said;-
$a[1]=$b[1];

It would appear that in php the increment in the left side of the assignment is processed prior to processing the right side of the assignment, whereas in C, neither increment occurs until after the assignment.
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-41
golotyuk at gmail dot com
13 years ago
Simple POST and PRE incremnt sample:

<?php

$b
= 5;
$a = ( ( ++$b ) > 5 ); // Pre-increment test
echo (int)$a;

$b = 5;
$a = ( ( $b++ ) > 5 ); // Post-increment test
echo (int)$a;

?>

This will output 10, because of the difference in post- and pre-increment operations
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