PHP 5.4.33 Released

reset

(PHP 4, PHP 5)

resetEstablece el puntero interno de un array a su primer elemento

Descripción

mixed reset ( array &$array )

reset() rebobina el puntero interno de un array al primer elemento y devuelve el valor del primer elemento del array.

Parámetros

array

El array de entrada.

Valores devueltos

Devuelve el valor del primer elemento de un array o FALSE si el array está vacío.

Ejemplos

Ejemplo #1 Ejemplo de reset()

<?php

$array 
= array('paso uno''paso dos''paso tres''paso cuatro');

// Por defecto, el puntero está en el primer elemento
echo current($array) . "<br />\n"// "paso uno"

// Omite dos pasos
next($array);
next($array);
echo 
current($array) . "<br />\n"// "paso tres"

// Resetea el puntero, empieza otra vez en paso uno
reset($array);
echo 
current($array) . "<br />\n"// "paso uno"

?>

Ver también

  • current() - Devuelve el elemento actual en un array
  • each() - Devolver el par clave/valor actual de un array y avanzar el cursor del array
  • end() - Establece el puntero interno de un array a su último elemento
  • next() - Avanza el puntero interno de un array
  • prev() - Rebobina el puntero interno del array

add a note add a note

User Contributed Notes 10 notes

up
10
Mladen Janjetovic
1 year 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) {...}
up
9
milo at mdlwebsolutions dot com
2 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.
up
10
kendsnyder at gmail dot com
4 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
up
7
Alexandre Koriakine
8 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
}

}
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4
m dot lebkowski+php at gmail dot com
8 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.
up
4
Colin
8 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.
up
2
leaetherstrip at inbox dot NOSPAMru
9 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]
up
0
gardnerjohng at gmail dot com
3 days 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.
up
0
Anonymous
8 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;
}
?>
up
0
kk at shonline dot de
16 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);
  }
}
?>
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