array_walk
(PHP 4, PHP 5, PHP 7, PHP 8)
array_walk — Apply a user supplied function to every member of an array
Description
Applies the user-defined callback function to each
element of the array array.
array_walk() is not affected by the internal array
pointer of array. array_walk()
will walk through the entire array regardless of pointer position.
Parameters
-
array -
The input array.
-
callback -
Typically,
callbacktakes on two parameters. Thearrayparameter's value being the first, and the key/index second.Note:
If
callbackneeds to be working with the actual values of the array, specify the first parameter ofcallbackas a reference. Then, any changes made to those elements will be made in the original array itself.Note:
Many internal functions (for example strtolower()) will throw a warning if more than the expected number of argument are passed in and are not usable directly as a
callback.Only the values of the
arraymay potentially be changed; its structure cannot be altered, i.e., the programmer cannot add, unset or reorder elements. If the callback does not respect this requirement, the behavior of this function is undefined, and unpredictable. -
arg -
If the optional
argparameter is supplied, it will be passed as the third parameter to thecallback.
Return Values
Returns true.
Errors/Exceptions
As of PHP 7.1.0, an ArgumentCountError will be thrown if the callback function
requires more than 2 parameters (the value and key of the array member),
or more than 3 parameters if the arg is also passed.
Previously, in this case
an error of level E_WARNING would be generated each time
array_walk() calls callback.
Changelog
| Version | Description |
|---|---|
| 8.0.0 |
If callback expects the second or third parameter to be passed
by reference, this function will now emit an E_WARNING.
|
Examples
Example #1 array_walk() example
<?php
$fruits = array("d" => "lemon", "a" => "orange", "b" => "banana", "c" => "apple");
function test_alter(&$item1, $key, $prefix)
{
$item1 = "$prefix: $item1";
}
function test_print($item2, $key)
{
echo "$key. $item2\n";
}
echo "Before ...:\n";
array_walk($fruits, 'test_print');
array_walk($fruits, 'test_alter', 'fruit');
echo "... and after:\n";
array_walk($fruits, 'test_print');
?>
The above example will output:
Before ...: d. lemon a. orange b. banana c. apple ... and after: d. fruit: lemon a. fruit: orange b. fruit: banana c. fruit: apple
Example #2 array_walk() example using anonymous function
<?php
$elements = ['a', 'b', 'c'];
array_walk($elements, function ($value, $key) {
echo "{$key} => {$value}\n";
});
?>
The above example will output:
0 => a 1 => b 2 => c
See Also
- array_walk_recursive() - Apply a user function recursively to every member of an array
- iterator_apply() - Call a function for every element in an iterator
- list() - Assign variables as if they were an array
- each() - Return the current key and value pair from an array and advance the array cursor
- call_user_func_array() - Call a callback with an array of parameters
- array_map() - Applies the callback to the elements of the given arrays
- foreach
