list

(PHP 4, PHP 5, PHP 7, PHP 8)

listAssegna valori a delle variabili come se fossero un array

Descrizione

list(mixed $var1, mixed ...$... = ?): array

Come array(), questa non è in realtà una funzione, bensì un costrutto del linguaggio. list() è usata per assegnare valori ad una lista di variabili in una sola operazione.

Nota:

list() funziona solo su array numerici e si aspetta che gli indici numerici partano da 0.

Avviso

In PHP 5, list() assegna i valori partendo dal parametro più a destra. In PHP 7, list() comincia dal parametro più a sinistra.

Se si stanno usando variabili semplici, non ci si deve preoccupare di questo comportamento. Ma se si stanno usando array con indici ci si aspetta che l'ordine degli indici nell'array sia lo stesso scritto nella funzione list() da sinitra a destra; non è il caso in PHP 5, dal momento che sono assegnati in ordine inverso.

In generale, è sconsigliato fare affidamento su uno specifico ordine di operazioni, dal momento che questo può cambiare in futuro.

Avviso

La modifica dell'array durante l'esecuzione di list() (es. usando list($a, $b) = $b ha un comportamento indefinito.

Elenco dei parametri

var1

Una variabile.

Valori restituiti

Restituisce l'array assegnato.

Esempi

Example #1 esempio di list()

<?php

$info 
= array('caffè''scuro''caffeina');

// assegna a tutte le variabili
list($bevanda$colore$componente) = $info;
echo 
"Il $bevanda è $colore e la $componente lo rende speciale.\n";

// assegna solo in parte
list($bevanda, , $componente) = $info;
echo 
"Il $bevanda ha la $componente.\n";

// oppure assegnamo solo l'ultima variabile
list( , , $componente) = $info;
echo
"Ho voglia di $componente!\n";

// list() non funziona con le stringhe
list($bar) = "abcde";
var_dump($bar); // NULL
?>

Example #2 Esempio di uso di list()

<table>
 <tr>
  <th>Nome dell'impiegato</th>
  <th>Stipendio</th>
 </tr>

<?php
$risultato 
$pdo_query("SELECT id, nome, stipendio FROM impiegati");
while (list(
$id$nome$stipendio) = $result->fetch(PDO::FETCH_NUM)) {
    echo (
" <tr>\n".
          
"  <td><a href=\"info.php?id=$id\">$nome</a></td>\n".
          
"  <td>$stipendio</td>\n".
          
" </tr>\n");
}

?>

</table>

Example #3 Utilizzare list() annidate

<?php

list($a, list($b$c)) = array(1, array(23));

var_dump($a$b$c);

?>
int(1)
int(2)
int(3)

Example #4 Utilizzo di list() con gli indici

<?php

$info 
= array('caffè''nero''caffeina');

list(
$a[0], $a[1], $a[2]) = $info;

var_dump($a);

?>

Restituisce il seguente risultato (si noti l'ordine degli elementi rispetto all'ordine con cui sono stati scritti nella sintassi di list()).

Output of the above example in PHP 7:

array(3) {
  [2]=>
  string(8) "caffeina"
  [1]=>
  string(4) "nero"
  [0]=>
  string(5) "caffè"
}

Output of the above example in PHP 5:

array(3) {
  [2]=>
  string(8) "caffeine"
  [1]=>
  string(5) "brown"
  [0]=>
  string(6) "coffee"
}

Example #5 list() e ordine delle definizioni dell'indice

L'ordine con il quale sono definiti gli indici dell'array da consumare da parte di list() è irrilevante.

<?php
$foo 
= array(=> 'a''foo' => 'b'=> 'c');
$foo[1] = 'd';
list(
$x$y$z) = $foo;
var_dump($foo$x$y$z);

Restituisce il seguente risultato (si noti l'ordine degli elementi in rapporto a quello con cui sono scritti nella sintassi di list()):

array(4) {
  [2]=>
  string(1) "a"
  ["foo"]=>
  string(1) "b"
  [0]=>
  string(1) "c"
  [1]=>
  string(1) "d"
}
string(1) "c"
string(1) "d"
string(1) "a"

Vedere anche:

  • each() - Restituisce la corrente coppia chiave/valore di un array e incrementa il puntatore dell'array
  • array() - Crea un array
  • extract() - Importa le variabili nella tabella dei simboli corrente da un array

add a note add a note

User Contributed Notes 24 notes

up
119
Rhamnia Mohamed
5 years ago
Since PHP 7.1, keys can be specified

exemple :
<?php
$array
= ['locality' => 'Tunis', 'postal_code' => '1110'];

list(
'postal_code' => $zipCode, 'locality' => $locality) = $array;

print
$zipCode; // will output 1110
print $locality; // will output Tunis
?>
up
87
carlosv775 at gmail dot com
5 years ago
In PHP 7.1 we can do the following:

<?php
   
[$a, $b, $c] = ['a', 'b', 'c'];
?>

Before, we had to do:

<?php
   
list($a, $b, $c) = ['a', 'b''c'];
?>
up
80
grzeniufication
8 years ago
The example showing that:

$info = array('kawa', 'brązowa', 'kofeina');
list($a[0], $a[1], $a[2]) = $info;
var_dump($a);

outputs:
array(3) {
[2]=>
string(8) "kofeina"
[1]=>
string(5) "brązowa"
[0]=>
string(6) "kawa"
}

One thing to note here is that if you define the array earlier, e.g.:
$a = [0, 0, 0];

the indexes will be kept in the correct order:

array(3) {
  [0]=>
  string(4) "kawa"
  [1]=>
  string(8) "brązowa"
  [2]=>
  string(7) "kofeina"
}

Thought that it was worth mentioning.
up
58
grzeniufication
5 years ago
<?php
/**
* It seems you can skip listed values.
* Here's an example to show what I mean.
*
* FYI works just as well with PHP 7.1 shorthand list syntax.
* Tested against PHP 5.6.30, 7.1.5
*/
$a = [ 1, 2, 3, 4 ];

// this is quite normal use case for list
echo "Unpack all values\n";
list(
$v1, $v2, $v3, $v4) = $a;
echo
"$v1, $v2, $v3, $v4\n";
unset(
$v1, $v2, $v3, $v4);

// this is what I mean:
echo "Skip middle\n";
list(
$v1, , , $v4) = $a;
echo
"$v1, $v2, $v3, $v4\n";
unset(
$v1, $v2, $v3, $v4);

echo
"Skip beginning\n";
list( , ,
$v3, $v4) = $a;
echo
"$v1, $v2, $v3, $v4\n";
unset(
$v1, $v2, $v3, $v4);

echo
"Skip end\n";
list(
$v1, $v2, , ) = $a;
echo
"$v1, $v2, $v3, $v4\n";
unset(
$v1, $v2, $v3, $v4);

echo
"Leave middle\n";
list( ,
$v2, $v3, ) = $a;
echo
"$v1, $v2, $v3, $v4\n";
unset(
$v1, $v2, $v3, $v4);
up
66
megan at voices dot com
9 years ago
As noted, list() will give an error if the input array is too short. This can be avoided by array_merge()'ing in some default values. For example:

<?php
$parameter
= 'name';
list(
$a, $b ) = array_merge( explode( '=', $parameter ), array( true ) );
?>

However, you will have to array_merge with an array long enough to ensure there are enough elements (if $parameter is empty, the code above would still error).

An alternate approach would be to use array_pad on the array to ensure its length (if all the defaults you need to add are the same).

<?php
    $parameter
= 'bob-12345';
    list(
$name, $id, $fav_color, $age ) = array_pad( explode( '-', $parameter ), 4, '' );
   
var_dump($name, $id, $fav_color, $age);
/* outputs
string(3) "bob"
string(5) "12345"
string(0) ""
string(0) ""
*/
?>
up
72
chris at chlab dot ch
10 years ago
The example states the following:
<?php
// list() doesn't work with strings
list($bar) = "abcde";
var_dump($bar);
// output: NULL
?>

If the string is in a variable however, it seems using list() will treat the string as an array:
<?php
$string
= "abcde";
list(
$foo) = $string;
var_dump($foo);
// output: string(1) "a"
?>
up
49
svennd
9 years ago
The list() definition won't throw an error if your array is longer then defined list.
<?php

list($a, $b, $c) = array("a", "b", "c", "d");

var_dump($a); // a
var_dump($b); // b
var_dump($c); // c
?>
up
30
pemapmodder1970 at gmail dot com
6 years ago
list() can be used with foreach

<?php
$array
= [[1, 2], [3, 4], [5, 6]];

foreach(
$array as list($odd, $even)){
    echo
"$odd is odd; $even is even", PHP_EOL;
}
?>

The output:
===
1 is odd; 2 is even
3 is odd; 4 is even
5 is odd; 6 is even
up
2
mark at manngo dot net
1 year ago
For PHP 7.1 on, the documentation states that integer and string keys can be mixed, but that elements with and without keys cannot. Here is an example, using data from getimagesize() with mixed keys:

<?php
    $data
=[
       
0=> 160,
       
1 => 120,
       
2 => 2,
       
3 => 'width="160" height="120"',
       
'mime' => 'image/jpeg'
   
];
    list(
0=>$width,1=>$height,2=>$type,3=>$dimensions,'mime'=>$mime)=$data;
?>

Here, the numeric keys also need to be specified, as if the whole array is treated as an associative array.

As noted elsewhere, the list() operator can be written in array format:

<?php
   
[0=>$width,1=>$height,2=>$type,3=>$dimensions,'mime'=>$mime]=$data;
?>
up
21
john at jbwalker dot com
8 years ago
The list construct seems to look for a sequential list of indexes rather taking elements in sequence. What that obscure statement means is that if you unset an element, list will not simply jump to the next element and assign that to the variable but will treat the missing element as a null or empty variable:

    $test = array("a","b","c","d");
    unset($test[1]);
    list($a,$b,$c)=$test;
    print "\$a='$a' \$b='$b' \$c='$c'<BR>";

results in:
$a='a' $b='' $c='c'

not:
$a='a' $b='c' $c='d'
up
5
Paul Marti
3 years ago
Since 7.1.0, you can use an array directly without list():

<?php
[$test, $test2] = explode(",", "hello, world");
echo
$test . $test2; // hello, world
?>
up
1
fredsaavedra at hotmail dot com
2 years ago
Easy way to get actual date and time values in variables.

list($day,$month,$year,$hour,$minute,$second) = explode('-',date('d-m-Y-G-i-s'));
echo "$day-$month-$year $hour".":".$minute.":".$second;
up
1
vike2000 at gmail dot com
2 years ago
Setting it like <?php list($var1,$varN) = null ?> does _not_ raise an E_NOTICE (or other error) and afaics effectively equals an https://php.net/function.unset of $var1,$varN.

I note this as contrasting with the fact that PHP triggers an E_NOTICE about "Undefined offset" "if there aren't enough array elements to fill the list()", as attow documented for https://php.net/control-structures.foreach#control-structures.foreach.list and here only noted in https://php.net/function.list#122951 by Mardaneus.

For completeness, a bash(1) (v5.0 or 4.3 on macos10.13) cli test producing the same result for all my PHP-versions (installed via macports.org) follows. It's also tested with php7.3 using bash5.0 on Debian10:
bash --noprofile --norc -c 'for php in php{{53..56},{70..73}};do for literal in "array()" null;do echo -n $php …=$literal:&&$php -n -d error_reporting=E_ALL -r "var_dump(list(\$var)=$literal);";done;done'

# Above produces the same result pairs per version from:
php53 …=array():
Notice: Undefined offset: 0 in Command line code on line 1
array(0) {
}
# ... to:
php73 …=null:NULL
up
5
blazej
5 years ago
From PHP Version 7.1 you can specify keys in list(), or its new shorthand [] syntax. This enables destructuring of arrays with non-integer or non-sequential keys.

<?php
$data
= [
    [
"id" => 1, "name" => 'Tom'],
    [
"id" => 2, "name" => 'Fred'],
];

// list() style
list("id" => $id1, "name" => $name1) = $data[0];

// [] style
["id" => $id1, "name" => $name1] = $data[0];

// list() style
foreach ($data as list("id" => $id, "name" => $name)) {
   
// logic here with $id and $name
}

// [] style
foreach ($data as ["id" => $id, "name" => $name]) {
   
// logic here with $id and $name
}
up
4
contato at tobias dot ws
4 years ago
Since PHP 7.1 the [] may now be used as an alternative to the existing list() syntax:

<?php
[$number, $message] = explode('|', '123|Hello World!');
?>
up
2
petru at fuxspam dot xtremeweb dot ro
4 years ago
This is something I haven't seen in documentation.

Since PHP 7.1, you can use short-hand list unpacking using square brackets, just like short-hand array declaration:

<?php

$foo
= ['a', 'b', 'c'];

// short-hand array definition
[$a, $b, $c] = $foo;
echo
$a; // displays "a"

// it's same like:
list($x, $y, $z) = $foo;
echo
$x; // displays "a"

?>
up
3
anthony dot ossent at live dot fr
6 years ago
a simple example of use to swap two variables :

$a = 'hello';
$b = 'world';

list($a, $b) = [$b, $a];

echo $a . ' ' . $b; //display "world hello"

another example :

function getPosition($x, $y, $z)
{
   // ... some operations like $x++...
   return [$x, $y, $z];
}

list($x, $y, $z) = getPosition($x ,$y, $z);
up
2
Mardaneus
4 years ago
Unless you specify keys when using list() it expects the array being fed into it to start at 0.

So having the following code will result in a notice level warning "Undefined offset: 0" and variables not filling as expected

<?php
list($c1, $c2, $c3) = array [1 =>'a', 2 => 'b', 3 => 'c'];

var_dump($c1); // NULL
var_dump($c2); // string(1) "a"
var_dump($c3); // string(1) "b"

?>
up
2
Dean
6 years ago
UNDOCUMENTED BEHAVIOR:

    list($a,$b,$c) = null;

in fact works like:

    $a = null; $b = null; $c = null;

...So correspondingly:

    list($rows[]) = null;

Will increment count($rows), just as if you had executed $rows[] = null;

Watch out for this (for example) when retrieving entire tables from a database, e.g.

    while (list($rows[]) = $mysqlresult->fetch_row());

This will leave an extra 'null' entry as the last element of $rows.
up
0
diyor024 at gmail dot com
1 year ago
Don't miss simple array pattern matching since php 7

<?php

[$a] = ['hello!'];
var_dump($a); // 'hello!'

$arr = [4 => 50];
[
4 => $fifty] = $arr;
var_dump($fifty); // 50

$multidimensionalArray = [['id' => 15, 'email' => 'diyor024@gmail.com']];
[[
'id'  => $id, 'email' => $email]] = $multidimensionalArray;
var_dump($id, $email); // 15 diyor024@gmail.com

?>
up
0
samraskul at gmail dot com
1 year ago
list($a, $b, $c) = ["blue", "money", 32];

shortcut:

[$a, $b, $c] = ["blue", "money", 32];
up
-1
sergey dot leonidovich dot shevchenko at gmail dot com
1 year ago
['a' => $x, 'b' => $y] = ['a' => 1, 'b' => 2];

echo $x . '-' . $y; // 1-2
up
0
Colin Guthrie
7 years ago
If you want use the undefined behaviour as you might expect it e.g. if you want:

  $b = ['a','b']; list($a, $b) = $b;

to result in $a=='a' and $b=='b', then you can just cast $b to an array (even although it already is) to create a copy. e.g.

  $b = ['a','b']; list($a, $b) = (array)$b;

and get the expected results.
up
-3
JD
3 years ago
As of PHP 7.3, lists now support array destructuring - see here: https://www.php.net/manual/en/migration73.new-features.php
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