list
(PHP 4, PHP 5)
list — Assign variables as if they were an array
Description
Like array(), this is not really a function, but a language construct. list() is used to assign a list of variables in one operation.
Parameters
-
var1 -
A variable.
Return Values
Returns the assigned array.
Examples
Example #1 list() examples
<?php
$info = array('coffee', 'brown', 'caffeine');
// Listing all the variables
list($drink, $color, $power) = $info;
echo "$drink is $color and $power makes it special.\n";
// Listing some of them
list($drink, , $power) = $info;
echo "$drink has $power.\n";
// Or let's skip to only the third one
list( , , $power) = $info;
echo "I need $power!\n";
// list() doesn't work with strings
list($bar) = "abcde";
var_dump($bar); // NULL
?>
Example #2 An example use of list()
<table>
<tr>
<th>Employee name</th>
<th>Salary</th>
</tr>
<?php
$result = $pdo->query("SELECT id, name, salary FROM employees");
while (list($id, $name, $salary) = $result->fetch(PDO::FETCH_NUM)) {
echo " <tr>\n" .
" <td><a href=\"info.php?id=$id\">$name</a></td>\n" .
" <td>$salary</td>\n" .
" </tr>\n";
}
?>
</table>
Example #3 Using nested list()
<?php
list($a, list($b, $c)) = array(1, array(2, 3));
var_dump($a, $b, $c);
?>
int(1) int(2) int(3)
Example #4 Using list() with array indices
<?php
$info = array('coffee', 'brown', 'caffeine');
list($a[0], $a[1], $a[2]) = $info;
var_dump($a);
?>
Gives the following output (note the order of the elements compared in which order they were written in the list() syntax):
array(3) {
[2]=>
string(8) "caffeine"
[1]=>
string(5) "brown"
[0]=>
string(6) "coffee"
}
Notes
list() assigns the values starting with the right-most parameter. If you are using plain variables, you don't have to worry about this. But if you are using arrays with indices you usually expect the order of the indices in the array the same you wrote in the list() from left to right; which it isn't. It's assigned in the reverse order.
Modification of the array during list() execution (e.g. using list($a, $b) = $b) results in undefined behavior.
Note:
list() only works on numerical arrays and assumes the numerical indices start at 0.
- PHP Руководство
- Функции по категориям
- Индекс функций
- Справочник функций
- Расширения, относящиеся к переменным и типам
- Массивы
- array_change_key_case
- array_chunk
- array_column
- array_combine
- array_count_values
- array_diff_assoc
- array_diff_key
- array_diff_uassoc
- array_diff_ukey
- array_diff
- array_fill_keys
- array_fill
- array_filter
- array_flip
- array_intersect_assoc
- array_intersect_key
- array_intersect_uassoc
- array_intersect_ukey
- array_intersect
- array_key_exists
- array_keys
- array_map
- array_merge_recursive
- array_merge
- array_multisort
- array_pad
- array_pop
- array_product
- array_push
- array_rand
- array_reduce
- array_replace_recursive
- array_replace
- array_reverse
- array_search
- array_shift
- array_slice
- array_splice
- array_sum
- array_udiff_assoc
- array_udiff_uassoc
- array_udiff
- array_uintersect_assoc
- array_uintersect_uassoc
- array_uintersect
- array_unique
- array_unshift
- array_values
- array_walk_recursive
- array_walk
- array
- arsort
- asort
- compact
- count
- current
- each
- end
- extract
- in_array
- key_exists
- key
- krsort
- ksort
- list
- natcasesort
- natsort
- next
- pos
- prev
- range
- reset
- rsort
- shuffle
- sizeof
- sort
- uasort
- uksort
- usort
Коментарии
The example states the following:
<?php
// list() doesn't work with strings
list($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"
?>
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
?>
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) ""
*/
?>
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'
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.
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.
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.
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
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, $z);
In PHP 7.1 we can do the following:
<?php
[$a, $b, $c] = ['a', 'b', 'c'];
?>
Before, we had to do:
<?php
list($a, $b, $c) = ['a', 'b', 'c'];
?>
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
?>
<?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);
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 $name
}
Since PHP 7.1 the [] may now be used as an alternative to the existing list() syntax:
<?php
[$number, $message] = explode('|', '123|Hello World!');
?>
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 $x; // displays "a"
?>
Unless you specify keys when using list() it expects the array being fed into it to start at 0.
So having the following code will result in a notice level warning "Undefined offset: 0" and variables not filling as expected
<?php
list($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"
?>
Since 7.1.0, you can use an array directly without list():
<?php
[$test, $test2] = explode(",", "hello, world");
echo $test . $test2; // hello, world
?>
As of PHP 7.3, lists now support array destructuring - see here: https://www.php.net/manual/en/migration73.new-features.phpSetting it like <?php list($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
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;
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]=$data;
?>
list($a, $b, $c) = ["blue", "money", 32];
shortcut:
[$a, $b, $c] = ["blue", "money", 32];
Don't miss simple array pattern matching since php 7
<?php
[$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
?>
It can be convenient to specify a default value in case an element is missing in the list. You can use operator + for this:
<?php
$someArray = ['color' => 'orange'];
['color' => $color, 'size' => $size] = $someArray + ['color' => null, 'size' => null];
?>
This will avoid the warning `Undefined array key "size"` you would encounter otherwise.