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.
(PHP 4, PHP 5, PHP 7, PHP 8)
reset — Establece el puntero interno de un array a su primer elemento
reset() rebobina el puntero interno de un array
al primer elemento y devuelve el valor del primer elemento del array.
arrayEl array de entrada.
Devuelve el valor del primer elemento de un array o false si el array
está vacío.
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"
?>
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($b)); //bool(true)
?>
So don't count on a false return being an empty array.
As for taking first key of an array, it's much more efficient to RESET and then KEY, rather then RESET result of ARRAY_KEYS (as sugested by gardnerjohng at gmail dot com).
<?php
reset($someArray);
echo key($someArray);
?>
This will give the same result but is much much faster. Larger arrays, better performance. Tested on 100-elements long array with 16 times faster results.
Also it's good to reset this way the multidimentional arrays:
reset($voo2['moder']);
while (list($key, $value) = each ($voo2['moder'])) {
reset($voo2['moder'][$key]);
while (list($key1, $value1) = each ($voo2['moder'][$key])) {
#do what u want
}
}
Note that you can't use pointer here. It will reset the iteration counter in this case.
foreach($array as $key=>&$value) {...}
Use standard foreach instead
foreach($array as $key=>$value) {...}
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]
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($properties); // => 'colour'
?>
I prefer this solution as you don't have to create the keys array. This should (not measured) improve performance on large arrays.
Info:
Following code gives a strict warning in 5.4.45
return reset(array_keys($result['node']));
"Strict warning: Only variables should be passed by reference"
So should be:
$keys = array_keys($result['node']);
return reset($keys);
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.
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.
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
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.
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.