数组 函数
在线手册：中文 英文
PHP手册

reset

(PHP 4, PHP 5)

reset — 将数组的内部指针指向第一个单元

说明

mixed reset ( array &$array )

reset() 将 array 的内部指针倒回到第一个单元并返回第一个数组单元的值，如果数组为空则返回 FALSE。

Example #1 reset() 例子

<?php

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

// by default, the pointer is on the first element
echo current($array) . "<br />\n"; // "step one"

// skip two steps
next($array);
next($array);
echo current($array) . "<br />\n"; // "step three"

// reset pointer, start again on step one
reset($array);
echo current($array) . "<br />\n"; // "step one"

?>

参见 current()，each()，end()，next() 和 prev()。

数组 函数
在线手册：中文 英文
PHP手册
PHP手册 - N: 将数组的内部指针指向第一个单元

用户评论:

milo at mdlwebsolutions dot com (04-Apr-2012 06:22)

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.

kendsnyder at gmail dot com (08-Feb-2010 04:12)

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

steffen schomberg (17-Jul-2007 01:32)

The following method resets every array contained in a multi-dimensional array recursively. It takes the multi-dimensional array as parameter.

function Array_Dimensional_Reset(&$arrRef) {
    foreach ($arrRef as $key=>$val) {
        if (is_array($val)) {
            $this->Array_Dimensional_Reset($val);
            reset($arrRef[$key]);
        }
    }
}

m dot lebkowski+php at gmail dot com (03-Aug-2006 09:58)

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.

Colin (06-Jun-2006 04:11)

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.

(27-Feb-2006 09:20)

I wrote a nice function, which rotates values of array. Very useful for table rows where you have to rotate colors

<?php
function rotate(&$array) {
    $item = current($array);
    if (!next($array)) reset($array);  
    return $item;
}
?>

Alexandre Koriakine (18-Nov-2005 10:09)

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
}

}

s_p_a_mcatcher at hotmail dot com (02-Dec-2004 06:30)

Be aware that when using reset() to clear an element and key from an array, if auto-incrementing, the new array keys will not reset a key previously set:

$temparray[] = "0";
$temparray[] = "1";
$temparray[] = "2";
unset($temparray[2]);
$temparray[] = "2";
$temparray[] = "3";

print_r($temparray);

The above will return:
Array
(
    [0] => 0
    [1] => 1
    [3] => 2
    [4] => 3
)

When attempting something like this, its better to use array_pop().

hope it helped

leaetherstrip at inbox dot NOSPAMru (17-Oct-2004 02:54)

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]

kevin at oceania dot net (19-Jul-2003 02:54)

Here is a simple example on how to combine 2 arrays. Here we use array_combine() to create list of months and there respective month number. The same result could just as easily be achieved with array('1'=>'January') etc.

<?php
                                                                                                             
  // make it or break it
  error_reporting(E_ALL);
                                                                                                             
  // create and array of keys
  $keys = range(1,12);
                                                                                                             
  // create an array of months
  $months = array(
  'January',
  'February',
  'March',
  'April',
  'May',
  'June',
  'July',
  'August',
  'September',
  'October',
  'November',
  'December'
);
                                                                                                             
  // combine the arrays
  $combined_array = array_combine($keys, $months);
                                                                                                             
  // echo out the results
  foreach($combined_array as $k=>$v){ echo $k.' -> '.$v.'<br />'; }
                                                                                                             
?>

jules (12-Jun-2003 08:29)

Be aware that if you give an empty array to reset(), what you'll get back is a boolean. consider...

      $myarray = array();
      $ret = reset($myarray);
      echo 'reset has type '. gettype($ret) .' and val * '. $ret;
      if( $ret )
      {
        echo '*. But it evaluates true';
      }
      else
      {
        echo '*. It evaluates false';
      }
      if( is_null($ret) )
      {
        echo ', and appears null';
      }
      {
        echo ', and appears not null';
      }
     
      echo '.';

<output>
reset has type boolean and val * *. It evaluates false, and appears not null.
</output>

<bleaugh/>

kk at shonline dot de (30-Jul-1998 01:22)

When used on a scalar or unset value, reset() spews warning messages. This is often a problem when accessing arrays generated from HTML form input data: these are scalar or unset if the user didn't enter sufficient information.

You can silence these error messages by prefixing an @ (at sign) to reset(), but it is better style to protect your reset() and the following array traversal with an if (isset()). Example code:

<?php
if (isset($form_array)) {
  reset($form_array);
  while (list($k, $v) = each($form_array) {
    do_something($k, $v);
  }
}
?>