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reset

(PHP 4, PHP 5, PHP 7)

reset — Set the internal pointer of an array to its first element

Description

reset ( array &$array ) : mixed

reset() rewinds array's internal pointer to the first element and returns the value of the first array element.

Parameters

array: The input array.

Return Values

Returns the value of the first array element, or FALSE if the array is empty.

Warning

This function may return Boolean FALSE, but may also return a non-Boolean value which evaluates to FALSE. Please read the section on Booleans for more information. Use the === operator for testing the return value of this function.

Examples

Example #1 reset() example


<?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"

?>

Notes

Note: The return value for an empty array is indistinguishable from the return value in case of an array which has a boolean FALSE first element. To properly check the value of the first element of an array which may contain FALSE elements, first check the count() of the array, or check that key() is not NULL, after calling reset().

User Contributed Notes 13 notes

down

milo at mdlwebsolutions dot com ¶

7 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

Bartek Ferek ¶

3 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

kk at shonline dot de ¶

21 years ago


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);

  }

}

?>

down

Alexandre Koriakine ¶

13 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

Mladen Janjetovic ¶

6 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

m dot lebkowski+php at gmail dot com ¶

13 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

kendsnyder at gmail dot com ¶

9 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

leaetherstrip at inbox dot NOSPAMru ¶

14 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 ¶

3 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

arne dot ludwig at posteo dot de ¶

4 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

-1

gardnerjohng at gmail dot com ¶

5 years ago


If you need an easy way to retrieve the first *key* in an array (instead of the value), it can be done like this:

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

    #    Will output "colour".
    echo reset(array_keys($properties));
?>
Potentially helpful for configuration files that define a sequence of items as an associative array.

down

-2

Colin ¶

13 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.

down

-13

Anonymous ¶

13 years ago


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; 
} 
?>

add a note

reset

Description

Parameters

Return Values

Examples

Notes

See Also

User Contributed Notes 13 notes