reset

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

reset — Встановлює внутрішній вказівних масиву на його перший елемент

Опис

reset(array|object &$array): mixed

reset() переміщує внутрішній вказівник масиву array до його першого елемента та повертає значення цього елемента.

Параметри

array: Вхідний масив.

Значення, що повертаються

Повертає значення першого елемента масиву або false, якщо масив порожній.

Увага

Ця функція може повертати як логічне false, так і не логічне значення, яке прирівнюється до false. Докладніше про це описано в розділі Логічні типи даних. Для перевірки значення, яке повертає ця функція, використовується оператор ===.

Журнал змін

Версія	Опис
8.1.0	Виклик цієї функції для об'єктів є застарілим. Краще перетворити object в array, застосувавши get_mangled_object_vars(), або використати методи класу, який імплементує Iterator, наприклад ArrayIterator.
7.4.0	Примірники класів SPL тепер розглядаються як порожні об'єкти, які не мають властивостей, замість виклику метода інтерфейсу Iterator з такою ж назвою, як і в цієї функції.

Приклади

Приклад #1 Використання reset()

<?php

$array = array('крок перший', 'крок другий', 'крок третій', 'крок четвертий');

// Початково вказівник знаходиться на першому елементі
echo current($array) . "<br />\n"; // "крок перший"

// Пропустимо два кроки
next($array);
next($array);
echo current($array) . "<br />\n"; // "крок третій"

// Перевстановлення вказівника, починається знову з "крок перший"
reset($array);
echo current($array) . "<br />\n"; // "крок перший"

?>

Примітки

Зауваження: Значення, що повертається для порожнього масиву, таке ж, як для масиву, у якого перший елемент — bool false. Щоб точно визначити, що значення першого елемента масиву може бути false, треба поміряти() масив або перевірити, чи не повертає функція key() null після виклику reset().

Прогляньте також

current() - Return the current element in an array
each() - Return the current key and value pair from an array and advance the array cursor
end() - Set the internal pointer of an array to its last element
next() - Advance the internal pointer of an array
prev() - Rewind the internal array pointer
array_key_first() - Gets the first key of an array

Improve This Page

Learn How To Improve This Page • Submit a Pull Request • Report a Bug

＋add a note

User Contributed Notes 11 notes

down

milo at mdlwebsolutions dot com ¶

12 years ago

GOTCHA: If your first element is false, you don't know whether it was empty or not.

<?php

$a = array();
$b = array(false, true, true);
var_dump(reset($a) === reset($b)); //bool(true)

?>

So don't count on a false return being an empty array.

down

turabgarip at gmail dot com ¶

3 years ago

Since reset() returns the first "value" of the array beside resetting its internal pointer; it will return different results when it is combined with key() or used separately. Like;

<?php

$products = array(
    'biscuits' => array('biscuit1' => 'cobis', 'biscuit2' => 'probis'),
    'chocolates' => array('coco1' => 'cococ', 'coco2' => 'prococ'),
 );

echo key(reset($products['biscuits'])); // Fatal error

reset($products['biscuits']);
echo key($products['biscuits']); // Will print 'biscuit1'

?>

This is perfectly normal because in the first method, reset() returned the first "value" of the 'biscuits' element which is to be "cbosi". So key(string) will cause a fatal error. While in the second method you just reset the array and didn't use a returning value; instead you reset the pointer and than extracted the first key of an array.

If your array has more dimensions, it won't probably cause a fatal error but you will get different results when you combine reset() and key() or use them consecutively.

down

Bartek Ferek ¶

8 years ago

As for taking first key of an array, it's much more efficient to RESET and then KEY, rather then RESET result of ARRAY_KEYS (as sugested by gardnerjohng at gmail dot com).

<?php
reset($someArray);
echo key($someArray);
?>

This will give the same result but is much much faster. Larger arrays, better performance. Tested on 100-elements long array with 16 times faster results.

down

arne dot ludwig at posteo dot de ¶

9 years ago

In response to gardnerjohng's note to retrieve the first _key_ of an array:

To retrieve the first _key_ of an array you can use the combination of reset() and key().

<?php
    $properties = array(
        'colour'   => 'grey',
        'flavour'  => 'rubber',
        'name'     => 'Mouse Ball',
        'texture'  => 'rubbery'
    );

    reset($properties);
    echo key($properties); // => 'colour'
?>

I prefer this solution as you don't have to create the keys array. This should (not measured) improve performance on large arrays.

down

Mladen Janjetovic ¶

11 years ago

Note that you can't use pointer here. It will reset the iteration counter in this case.
foreach($array as $key=>&$value) {...} 
 

Use standard foreach instead 
foreach($array as $key=>$value) {...}

down

Alexandre Koriakine ¶

19 years ago

Also it's good to reset this way the multidimentional arrays:

reset($voo2['moder']);
while (list($key, $value) = each ($voo2['moder'])) {

reset($voo2['moder'][$key]);
while (list($key1, $value1) = each ($voo2['moder'][$key])) {
#do what u want
}

}

down

leaetherstrip at inbox dot NOSPAMru ¶

20 years ago

Note that reset() will not affect sub-arrays of multidimensional array.

For example,

<?php
    $arr = array(
        1 => array(2,3,4,5,6),
        2 => array(6,7,8,9,10)
    );
    
    while(list($i,) = each($arr))
    {
        echo "IN \$arr[$i]<br>";
        
        while(list($sub_i,$entry) = each($arr[$i]))
        {
            echo "\$arr[$i][$sub_i] = $entry<br>";
        }
    }
    
    reset($arr);

    // Do the same again
    while(list($i,) = each($arr))
    {
        echo "IN \$arr[$i]<br>";
        
        while(list($sub_i,$entry) = each($arr[$i]))
        {
            echo "\$arr[$i][$sub_i] = $entry<br>";
        }
    }
?>

will print

IN $arr[1]
$arr[1][0] = 2
$arr[1][1] = 3
$arr[1][2] = 4
$arr[1][3] = 5
$arr[1][4] = 6
IN $arr[2]
$arr[2][0] = 6
$arr[2][1] = 7
$arr[2][2] = 8
$arr[2][3] = 9
$arr[2][4] = 10
IN $arr[1]
IN $arr[2]

down

arne dot slabbinck at duo dot be ¶

9 years ago

Info:

Following code gives a strict warning in 5.4.45

      return reset(array_keys($result['node']));

"Strict warning: Only variables should be passed by reference"

So should be:

      $keys = array_keys($result['node']);
      return reset($keys);

down

kendsnyder at gmail dot com ¶

14 years ago

Don't use `reset()` to get the first value of an associative array. It works great for true arrays but works unexpectedly on Iterator objects. http://bugs.php.net/bug.php?id=38478

down

m dot lebkowski+php at gmail dot com ¶

18 years ago

Colin, there`s a better (IMO) way to solve your problem.
<?  
  // ...
  foreach($a as $k => &$d){}   // notice the "&"
  // ...
?>
It`s a new feature in PHP5 to use references in foreach loop. This way PHP isn`t making a copy of the array, so the internal pointer won`t be reset.

down

-1

Colin ¶

18 years ago

I had a problem with PHP 5.0.5 somehow resetting a sub-array of an array with no apparent reason.  The problem was in doing a foreach() on the parent array PHP was making a copy of the subarrays and in doing so it was resetting the internal pointers of the original array.

The following code demonstrates the resetting of a subarray:

<?
$a = array(
    'a' => array(
        'A', 'B', 'C', 'D',
    ),
    'b' => array(
        'AA', 'BB', 'CC', 'DD',
    ),
);

// Set the pointer of $a to 'b' and the pointer of 'b' to 'CC'
reset($a);
next($a);
next($a['b']);
next($a['b']);
next($a['b']);

var_dump(key($a['b']));
foreach($a as $k => $d)
{
}
var_dump(key($a['b']));
?>

The result of the two var dumps are 3 and 0, respectively.  Clearly the internal pointer of $a['b'] was reset by doing the foreach loop over $a.

Each time the foreach loop iterated over the 'a' and 'b' keys of $a it made a copy of $a['a'] and $a['b'] into $d which resetted the internal pointers of $a['a'] and $a['b'] despite making no obvious changes.

The solution is instead to iterate over the keys of $a.

<?
foreach(array_keys($a) as $k)
{
}
?>

and using $a[$k] (or creating an alias of $a[$k] as $d and dealing with the consequences of using aliases).

For the curious, I was implementing the Iterator interface on a dummy object and calling a global object to do the actual iteration (also to cope with PHP's lack of C-style pointers which when doing a $a = $b on objects would cause the data in $a to be inconsistent with the data in $b when modified).  Being that I had many dummy objects representing different data sets I chose to store each data set as a subarray contained within the global object.  To make this work each dummy object has to store a key (which can freely be duplicated without problems) that it passes to the global object when rewind, key, current, next, and valid were called on the dummy object.

Unfortunately for me, my key required to be more than just a simple string or number (if it was then it could be used to directly index the subarray of data for that object and problem avoided) but was an array of strings.  Instead, I had to iterate over (with a foreach loop) each subarray and compare the key to a variable stored within the subarray.

So by using a foreach loop in this manner and with PHP resetting the pointer of subarrays it ended up causing an infinite loop.

Really, this could be solved by PHP maintaining internal pointers on arrays even after copying.

＋add a note