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Operadores

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Un operador es algo que toma uno más valores (o expresiones, en la jerga de programación) y produce otro valor (de modo que la construcción en si misma se convierte en una expresión).

Los operadores se pueden agrupar de acuerdo con el número de valores que toman. Los operadores unarios toman sólo un valor, por ejemplo ! (el operador lógico de negación) o ++ (el operador de incremento). Los operadores binarios toman dos valores, como los familiares operadores aritméticos + (suma) y - (resta), y la mayoría de los operadores de PHP entran en esta categoría. Finalmente, hay sólo un operador ternario, ? :, el cual toma tres valores; usualmente a este se le refiere simplemente como "el operador ternario" (aunque podría tal vez llamarse más correctamente como el operador condicional).

Una lista completa de operadores de PHP sigue en la sección Precedencia de Operadores. La sección también explica la precedencia y asociatividad de los operadores, las cuales gobiernan exactamente cómo son evaluadas expresiones que contienen varios diferentes operadores.

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User Contributed Notes 7 notes

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209
Anonymous
14 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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20
yasuo_ohgaki at hotmail dot com
17 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 $str.
(PHP4.0.4pl1/Apache DSO/Linux, PHP4.0.5RC1/Apache DSO/W2K Server)
It's due to precedence, probably.
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0
figroc at gmail dot com
10 years ago
The variable symbol '$' 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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0
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' :
        (
$a == 4 ? 'four' : 'other') ) ) );
echo
"\n";
//prints 'two'
?>
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-26
me at robrosenbaum dot com
11 years ago
The scope resolution operator ::, which is missing from the list above, has higher precedence than [], and lower precedence than 'new'. This means that self::$array[$var] works as expected.
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-30
golotyuk at gmail dot com
12 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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-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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