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Assign variables as if they were an array
(PHP 4, PHP 5)
Example 312. list() examples<?phpExample 313. An example use of list()<table>Example 314. Using list() with array indices<?phpGives the following output (note the order of the elements compared in which order they were written in the list() syntax): array(3) {Related Examples ( Source code ) » list Examples ( Source code ) » React to Form action Examples ( Source code ) » Build query string based on form input Examples ( Source code ) » File based login Examples ( Source code ) » List all database Examples ( Source code ) » List all tables in a database Examples ( Source code ) » List Database, Table, and Field Examples ( Source code ) » Listing All Rows and Fields in a Table Examples ( Source code ) » Listing the Databases Available in a Connection Examples ( Source code ) » Connect to MySQL Examples ( Source code ) » Print MySQL processes information Examples ( Source code ) » use Column name in select statement as the variable name Examples ( Source code ) » Get all tables in a database Examples ( Source code ) » Listing Tables in a Database Examples ( Source code ) » Total number of fields in a table Examples ( Source code ) » Listing the Contents of a Directory with readdir() Code Examples / Notes » listergalvan
With regard to the note written by dolan at teamsapient dot com: You must take note that list() assigns variables starting from the rightmost one (as stated in the warning). That makes $record having the value "value4" and then $var1, $var2 and $var3 take their values from the "new" $record variable. It's clear that the behavior stated in the warning wasn't followed by version 5.0.4 (and perhaps previous versions?) jennevdmeer
This is a function simulair to that of 'list' it lists an array with the 'key' as variable name and then those variables contain the value of the key in the array. This is a bit easier then list in my opinion since you dont have to list up all variable names and it just names them as the key. <?php function lista($a) { foreach ($a as $k => $v) { $s = "global \$".$k; eval($s.";"); $s = "\$".$k ." = \"". $v."\""; eval($s.";"); } } ?> mortoray
There is no way to do reference assignment using the list function, therefore list assignment is will always be a copy assignment (which is of course not always what you want). By example, and showing the workaround (which is to just not use list): function &pass_refs( &$a ) { return array( &$a ); } $a = 1; list( $b ) = pass_refs( $a ); //* $a = 2; print( "$b" ); //prints 1 $ret = pass_refs( $a ); $b =& $ret[0]; $a = 3; print( "$b" ); //prints 3 *This is where some syntax like the following would be desired: list( &$b ) = pass_refs( $a ); or maybe: list( $b ) =& pass_refs( $a ); hw
The list() construct can be used within other list() constructs (so that it can be used to extract the elements of multidimensional arrays): <?php $matrix = array(array(1,2), array(3,4)); list(list($tl,$tr),list($bl,$br)) = $matrix; echo "$tl $tr $bl $br"; ?> Outputs "1 2 3 4". tobylewis
The list construct assigns elements from a numbered array starting from element zero. It does not assign elements from associative arrays. So $arr = array(); $arr[1] = 'x'; list($a, $b) = $arr; var_dump($a); //outputs NULL because there is no element [0] var_dump($b); //outputs 'x' and $arr = array('red'=>'stop','green'=>'go'); list($a, $b) = $arr; var_dump($a); //outputs NULL var_dump($b); //outputs NULL If there are not enough elements in the array for the variables in the list the excess variables are assigned NULL. If there are more elements in the array than variables in the list, the extra array elements are ignored without error. Also the warning above about order of assignment is confusing until you get used to php arrays. The order in which array elements are stored is the order in which elements are assigned to the array. So even in a numbered array if you assign $may_arr[2] before you assign $my_array[0] then element [2] will be in the array before [0]. This becomes apparent when using commands like, push, shift or foreach which work with the stored order of the elements. So the warning only applies when the variables in the list are themselves array elements which have not already been assigned to their array. tenz699
PhP manual's NOTE says: list() only works on numerical arrays and assumes the numerical indices start at 0. I'm finding it do works for associative arrays too,as below: <? $tenzin = array ("1" => "one", "2" => "two","3"=>"three"); while(list($keys,$values) = each($tenzin)) echo($keys." ".$values." "); ?> gives O/P 1 one 2 two 3 three tsarma webmaster
One way to use the list function with non-numerical keys is to use the array_values() function <?php $array = array ("value1" => "one", "value2" => "two"); list ($value1, $value2) = array_values($array); ?> rubein
Note: If you have an array full of arrays, you can't use list() in conjunction to foreach() when traversing said array, e.g. $someArray = array( array(1, "one"), array(2, "two"), array(3, "three") ); foreach($somearray as list($num, $text)) { ... } This, however will work foreach($somearray as $subarray) { list($num, $text) = $subarray; ... } nearsighted
list, coupled with while, makes for a handy way to populate arrays. while (list($repcnt[], $replnk[], $date[]) = mysql_fetch_row($seek0)) { // insert what you want to do here. } PHP will automatically assign numerical values for the array because of the [] signs after the variable. From here, you can access their row values by array numbers. eg. for ($i=0;$i<$rowcount;$i++) { echo "The title number $repcnt[$i] was written on $date[$i]."; } mick
It's worth noting that, as expected, list() does not have to have as many variables (and/or empty skips) as there are elements in the array. PHP will disregard all elements that there are no variables for. So: <?php $Array_Letters = array('A', 'B', 'C', 'D', 'E', 'F'); list($Letter_1, $Letter_2) = $Array_Letters; echo $Letter_1 . $Letter_2; ?> Will output: AB Mick hayley watson
In the code by tenz699 at hotmail dot com, the list() construct is taking values from the result of the each() function, not from the associative array; the example is therefore spurious. each() returns an array of four elements, indexed in the order 1, 'value', 0, 'key'. As noted in the documentation, the associative keys are ignored, and the numerically-indexed values are assigned in key order. <?php $array = array('foo'=>'bar'); $t = each($array); print_r($t); list($a,$b,$c,$d) = $t; var_dump($a); var_dump($b); var_dump($c); var_dump($d); ?> Output: Array ( [1] => bar [value] => bar [0] => foo [key] => foo ) string(3) "foo" string(3) "bar" NULL NULL jeronimo
If you want to swap values between variables without using an intermediary, try using the list() and array() language constructs. For instance: <? // Initial values. $biggest = 1; $smallest = 10; // Instead of using a temporary variable... $temp = $biggest; $biggest = $smallest; $smallest = $temp; // ...Just swap the values. list($biggest, $smallest) = array($smallest, $biggest); ?> This works with any number of variables; you're not limited to just two. Cheers, Jeronimo dolan
I noticed w/ version 5.1.2, the behavior of list() has changed (this occurred at some point between version 5.0.4 and 5.1.2). When re-using a variable name in list() that list() is being assigned to, instead of the values being assigned all at once, the reused variable gets overwritten before all the values are read. Here's an example: ** disclaimer: obviously this is sloppy code, but I want to point out the behavior change (in case anyone else comes across similar code) ** <? $data = array(); $data[] = array("value1", "value2", "value3", "value4"); $data[] = array("value1", "value2", "value3", "value4"); $data[] = array("value1", "value2", "value3", "value4"); $data[] = array("value1", "value2", "value3", "value4"); foreach($data as $record) { list($var1, $var2, $var3, $record) = $record; echo "var 1: $var1, var 2: $var2, var 3: $var3, record: $record\\n"; } ?> OUTPUT on version 5.0.4: var 1: value1, var 2: value2, var 3: value3, record: value4 var 1: value1, var 2: value2, var 3: value3, record: value4 var 1: value1, var 2: value2, var 3: value3, record: value4 var 1: value1, var 2: value2, var 3: value3, record: value4 OUTPUT on version 5.1.2: var 1: v, var 2: a, var 3: l, record: value4 var 1: v, var 2: a, var 3: l, record: value4 var 1: v, var 2: a, var 3: l, record: value4 var 1: v, var 2: a, var 3: l, record: value4 mzizka
Elements on the left-hand side that don't have a corresponding element on the right-hand side will be set to NULL. For example, <?php $y = 0; list($x, $y) = array("x"); var_dump($x); var_dump($y); ?> Results in: string(1) "x" NULL |
Change Language
array_change_key_case array_chunk 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_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 krsort ksort list natcasesort natsort next pos prev range reset rsort shuffle sizeof sort uasort uksort usort |
