International PHP Conference 2019 - Spring Edition

Operatori

Indice dei contenuti

Un operatore è un qualcosa che si posiziona tra uno o più valori (od espressioni, in gergo tecnico) e produce un'altro valore (in modo tale che la costruzione stessa diventi a sua volta un'espressione). i

Gli operatori possono essere raggruppati a seconda del numero di valori che trattano. Gli operatori unari quali richiedono un solo valore, ad esempio !i (l'operatore logico noti) oppure ++ (l'operatore di autoincremento). Gli operatori binari accettano due valor, come i familiari operatori aritmetici + (più) e - (meno), e la maggior parte degli operatori disponibili in PHP ricadono in questa categoria. Infine, esiste un solo operatore ternario, ? :, che accetta tre valori; viene normalmente chiamato "l'operatore ternario" (anche se potrebbe forse essere chiamato più precisamente operatore condizionale).

Una lista completa degli operatore è fornita nella sezione Precedenza degli operatori. Questa sezione spiega anche la precedenza degli operatori e l'associatività, che stabiliscono esattamente come le espressioni contenenti differenti operatori sono valutate ed eseguite.

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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 $str.
(PHP4.0.4pl1/Apache DSO/Linux, PHP4.0.5RC1/Apache DSO/W2K Server)
It's due to precedence, probably.
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-1
figroc at gmail dot com
10 years ago
The variable symbol '$' 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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-1
phpnet dot 20 dot dpnsubs at xoxy dot net
10 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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-31
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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-38
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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