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

reset — 配列の内部ポインタを先頭の要素にセットする

説明

reset(array|object &$array): mixed

reset() は、array の内部ポインタの先頭の要素に戻し、配列の最初の要素の値を返します。

パラメータ

array: 入力の配列。

戻り値

配列の最初の要素の値を返します。配列が空の場合 false を返します。

警告

この関数は論理値 false を返す可能性がありますが、false として評価される値を返す可能性もあります。詳細については論理値のセクションを参照してください。この関数の返り値を調べるには ===演算子を使用してください。

変更履歴

バージョン	説明
8.1.0	この関数を object に対してコールすることは、推奨されなくなりました。 object に対して最初に get_mangled_object_vars() を使って配列に変換するか、ArrayIterator のような Iterator を実装したクラスのメソッドを使ってください。
7.4.0	SPL クラスのインスタンスは、プロパティを持たない空のオブジェクトのように扱われるようになりました。これより前のバージョンでは、この関数と同じ名前の Iterator のメソッドをコールしていました。

例

例1 reset() の例

<?php

$array = array('step one', 'step two', 'step three', 'step four');

// デフォルトでは、ポインタは先頭要素を指しています
echo current($array) . "<br />\n"; // "step one"

// 次の２ステップをとばします
next($array);
next($array);
echo current($array) . "<br />\n"; // "step three"

// ポインタをリセットし、再度ステップ１開始します
reset($array);
echo current($array) . "<br />\n"; // "step one"

?>

注意

注意: 空の配列に対してこの関数を実行した場合の戻り値は、配列の先頭要素に bool false がある配列に対して実行した場合の戻り値と区別できません。配列の先頭に false が含まれている可能性がある値を適切にチェックするには、まず最初に配列の count() をチェックするか、 reset() を呼び出した後に、要素の key() が null でないことを確かめるようにしてください。

参考

current() - 配列内の現在の要素を返す
each() - 配列から現在のキーと値のペアを返して、カーソルを進める
end() - 配列の内部ポインタを最終要素にセットする
next() - 配列の内部ポインタを進める
prev() - 内部の配列ポインタをひとつ前に戻す
array_key_first() - 配列の最初のキーを得る

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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.

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reset

説明

パラメータ

戻り値

変更履歴

例

注意

参考

Found A Problem?

User Contributed Notes 11 notes