list
Like array() , this is not really a function, but a language construct. list() is used to assign a list of variables in one operation. Strings can not be unpacked and list() expressions can not be completely empty.
Note:
Before PHP 7.1.0, list() only worked on numerical arrays and assumes the numerical indices start at 0.
Parameters
Return Values
Returns the assigned array.
Changelog
| Version | Description |
|---|---|
| 7.3.0 | Support for reference assignments in array destructuring was added. |
| 7.1.0 | It is now possible to specify keys in list() . This enables destructuring of arrays with non-integer or non-sequential keys. |
Examples
Example #1 list() examples
$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()
$result = $pdo -> query ( «SELECT id, name FROM employees» );
while (list( $id , $name ) = $result -> fetch ( PDO :: FETCH_NUM )) echo «id: $id , name: $name \n» ;
>
?>
Example #3 Using nested list()
list( $a , list( $b , $c )) = array( 1 , array( 2 , 3 ));
Example #4 list() and order of index definitions
The order in which the indices of the array to be consumed by list() are defined is irrelevant.
$foo = array( 2 => ‘a’ , ‘foo’ => ‘b’ , 0 => ‘c’ );
$foo [ 1 ] = ‘d’ ;
list( $x , $y , $z ) = $foo ;
var_dump ( $foo , $x , $y , $z );
Gives the following output (note the order of the elements compared in which order they were written in the list() syntax):
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"
Example #5 list() with keys
As of PHP 7.1.0 list() can now also contain explicit keys, which can be given as arbitrary expressions. Mixing of integer and string keys is allowed; however, elements with and without keys cannot be mixed.
$data = [
[ «id» => 1 , «name» => ‘Tom’ ],
[ «id» => 2 , «name» => ‘Fred’ ],
];
foreach ( $data as [ «id» => $id , «name» => $name ]) echo «id: $id , name: $name \n» ;
>
echo PHP_EOL ;
list( 1 => $second , 3 => $fourth ) = [ 1 , 2 , 3 , 4 ];
echo » $second , $fourth \n» ;
The above example will output:
id: 1, name: Tom id: 2, name: Fred 2, 4
See Also
- each() — Return the current key and value pair from an array and advance the array cursor
- array() — Create an array
- extract() — Import variables into the current symbol table from an array
User Contributed Notes 25 notes
Since PHP 7.1, keys can be specified
exemple :
$array = [ ‘locality’ => ‘Tunis’ , ‘postal_code’ => ‘1110’ ];
list( ‘postal_code’ => $zipCode , ‘locality’ => $locality ) = $array ;
print $zipCode ; // will output 1110
print $locality ; // will output Tunis
?>
In PHP 7.1 we can do the following:
[ $a , $b , $c ] = [ ‘a’ , ‘b’ , ‘c’ ];
?>
Before, we had to do:
$info = array(‘kawa’, ‘brązowa’, ‘kofeina’);
list($a[0], $a[1], $a[2]) = $info;
var_dump($a);
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:
Thought that it was worth mentioning.
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:
$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).
$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 example states the following:
// 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:
$string = «abcde» ;
list( $foo ) = $string ;
var_dump ( $foo );
// output: string(1) «a»
?>
/**
* 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 );
list() can be used with foreach
$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
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:
The list() definition won’t throw an error if your array is longer then defined list.
list( $a , $b , $c ) = array( «a» , «b» , «c» , «d» );
var_dump ( $a ); // a
var_dump ( $b ); // b
var_dump ( $c ); // c
?>
Don’t miss simple array pattern matching since php 7
[ $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
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:
$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:
[ 0 => $width , 1 => $height , 2 => $type , 3 => $dimensions , ‘mime’ => $mime ]= $data ;
?>
Setting it like 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,>;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
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:
// 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»
Get a list of all available functions with PHP
PHP has the function get_defined_functions() which allows you to get a list of all the available system and user defined functions in an array. This post looks at how to use the get_defined_functions() function, the output from it and how to sort the list into alphabetical order.
Using get_defined_functions()
get_defined_functions() returns an array containing two keys: ‘internal’ and ‘user’. Each key contains a sub array containing a complete list of the available internal/system functions and the user defined functions respectively.
The following example illustrates this (the examples below assume we have two user defined functions called foo() and bar()):
print_r(get_defined_functions());
and an extract of the result:
Array ( [internal] => Array ( [0] => zend_version [1] => func_num_args [2] => func_get_arg [3] => func_get_args [4] => strlen [5] => strcmp . [1274] => xmlwriter_write_dtd_attlist [1275] => xmlwriter_output_memory [1276] => xmlwriter_flush ) [user] => Array ( [0] => foo [1] => bar ) )
Sorting the result into alphabetical order
If you want to sort the list of functions into alphabetical order, you could do this instead:
$functions = get_defined_functions(); sort($functions['internal']); sort($functions['user']); print_r($functions);
and an extract of the result:
Array ( [internal] => Array ( [0] => _ [1] => abs [2] => acos [3] => acosh [4] => addcslashes [5] => addslashes . [1274] => zend_logo_guid [1275] => zend_version [1276] => zlib_get_coding_type ) [user] => Array ( [0] => bar [1] => foo ) )
Conclusion
The get_defined_functions() function is a great way of getting a complete list of functions that are available on your install of PHP and from your own and 3rd party PHP libraries.