echo
My application was running out of memory (my hosting company limits PHP to 32MB). I have a string containing between 100 and 20000 triplets, separated by a space, with each triplet consisting of three double-precision numbers, separated by commas. Total size of the biggest string, with 20000 triplets, is about 1MB.
The application needs to split the string into triplets, then split the triplet into numbers. In C, this would take up about 480K (20000 times 3 x 8 bytes) for the final array. The intermediate array of strings shouldn't be much bigger than the long string itself (1MB). And I expect some overhead from PHP, say 300% to allow for indexes etc.
Well, PHP5 manages to run out of memory *at the first stage* (exploding the string on the space character). I'm expecting to get an array of 20000 strings, but it needs more than 32MB to store it. Amazing.
The workaround was easy and had the bonus of producing faster code (I compared it on a 10000 triplet string). Since in any case I had to split up the numeric triplets afterwards, I decided to use preg_match_all() on the original string. Despite the fact that the resulting "matches" array contains more data per element than the result of explode() - because it stores the matched triplet, plus its component numbers - it takes up far less memory.
Moral: be careful when using explode() on big strings, as it can also explode your memory usage.
explode
(PHP 4, PHP 5)
explode — Coupe une chaîne en segments
Description
array explode
( string $delimiter
, string $string
[, int $limit
] )
explode() retourne un tableau de chaînes, chacune d'elle étant une sous-chaîne du paramètre string extraite en utilisant le séparateur delimiter .
Liste de paramètres
- delimiter
-
Le séparateur.
- string
-
La chaîne initiale.
- limit
-
Si limit est défini et positif, le tableau retourné contient, au maximum, limit éléments, et le dernier élément contiendra le reste de la chaîne.
Si le paramètre limit est négatif, tous les éléments, excepté les -limit derniers éléments sont retournés.
Si limit vaut zéro, il est traité comme valant 1.
Bien que implode() puisse, pour des raisons historiques, accepter ces paramètres dans n'importe quel ordre, explode() ne le peut pas. Vous devez vous assurer que le paramètre delimiter soit placé avant le paramètre string .
Valeurs de retour
Si delimiter est une chaîne vide (""), explode() retournera FALSE. Si delimiter contient une valeur qui n'est pas contenue dans string ainsi qu'une valeur négative pour le paramètre limit , alors explode() retournera un tableau, contenant la chaîne string entière.
Historique
| Version | Description |
|---|---|
| 5.1.0 | Le paramètre limit peut désormais être négatif |
| 4.0.1 | Le paramètre limit a été ajouté |
Exemples
Exemple #1 Exemple avec explode()
<?php
// Exemple 1
$pizza = "piece1 piece2 piece3 piece4 piece5 piece6";
$pieces = explode(" ", $pizza);
echo $pieces[0]; // piece1
echo $pieces[1]; // piece2
// Exemple 2
$data = "foo:*:1023:1000::/home/foo:/bin/sh";
list($user, $pass, $uid, $gid, $gecos, $home, $shell) = explode(":", $data);
echo $user; // foo
echo $pass; // *
?>
Exemple #2 Exemple avec explode()
<?php
$str = 'one|two|three|four';
// limit positif
print_r(explode('|', $str, 2));
// limit négatif (depuis PHP 5.1)
print_r(explode('|', $str, -1));
?>
L'exemple ci-dessus va afficher :
Array
(
[0] => one
[1] => two|three|four
)
Array
(
[0] => one
[1] => two
[2] => three
)
Notes
Note: Cette fonction gère les chaînes binaires.
Voir aussi
- preg_split() - Éclate une chaîne par expression rationnelle
- str_split() - Convertit une chaîne de caractères en tableau
- str_word_count() - Compte le nombre de mots utilisés dans une chaîne
- strtok() - Coupe une chaîne en segments
- implode() - Rassemble les éléments d'un tableau en une chaîne
add a note
User Contributed Notesexplode
nick dot brown at free dot fr
15-Oct-2009 12:47
15-Oct-2009 12:47
Jrg Wagner
12-Oct-2009 11:28
12-Oct-2009 11:28
Here is a very concise example for a quote aware explode - substrings in quotes (or another definable enclosure char) are not exploded.
An additional parameter allows to determine whether the enclosure chars should be preserved within the resulting array elements. Please note that as of PHP 5.3 the str_getcsv function offers a built-in way to do this!
<?php
function csv_explode($delim=',', $str, $enclose='"', $preserve=false){
$resArr = array();
$n = 0;
$expEncArr = explode($enclose, $str);
foreach($expEncArr as $EncItem){
if($n++%2){
array_push($resArr, array_pop($resArr) . ($preserve?$enclose:'') . $EncItem.($preserve?$enclose:''));
}else{
$expDelArr = explode($delim, $EncItem);
array_push($resArr, array_pop($resArr) . array_shift($expDelArr));
$resArr = array_merge($resArr, $expDelArr);
}
}
return $resArr;
}
?>
Anonymous
29-Sep-2009 12:20
29-Sep-2009 12:20
Note to the previous example: we can do the whole string->array conversion using explode() exclusively.
<?php
// converts pure string into a trimmed keyed array
function string_2_array( $string, $delimiter = ',', $kv = '=>')
{
if ($element = explode( $delimiter, $string ))
{
// create parts
foreach ( $element as $key_value )
{
// key -> value pair or single value
$atom = explode( $kv, $key_value );
if( trim($atom[1]) )
{
$key_arr[trim($atom[0])] = trim($atom[1]);
}
else
{
$key_arr[] = trim($atom[0]);
}
}
}
else
{
$key_arr = false;
}
return $key_arr;
}
?>
Anonymous
03-Sep-2009 04:18
03-Sep-2009 04:18
<?php
// converts pure string into a trimmed keyed array
function string2KeyedArray($string, $delimiter = ',', $kv = '=>') {
if ($a = explode($delimiter, $string)) { // create parts
foreach ($a as $s) { // each part
if ($s) {
if ($pos = strpos($s, $kv)) { // key/value delimiter
$ka[trim(substr($s, 0, $pos))] = trim(substr($s, $pos + strlen($kv)));
} else { // key delimiter not found
$ka[] = trim($s);
}
}
}
return $ka;
}
} // string2KeyedArray
$string = 'a=>1, b=>23 , $a, c=> 45% , true,d => ab c ';
print_r(string2KeyedArray($string));
?>
Array
(
[a] => 1
[b] => 23
[0] => $a
[c] => 45%
[1] => true
[d] => ab c
)
Anonymous
11-Aug-2009 07:55
11-Aug-2009 07:55
If you are exploding string literals in your code that have a dollar sign ($) in it, be sure to use single-quotes instead of double-quotes, since php will not spare any chance to interpret the variable-friendly characters after the dollar signs as variables, leading to unintended consequences, the most typical being missing characters.
<?php
$doubleAr = explode(" ", "The $quick brown fox");
$singleAr = explode(" ", 'The $quick brown fox');
echo $doubleAr[1]; // prints "";
echo $singleAr[1]; // prints "$quick";
?>
vzverev at nm dot ru
24-Jul-2009 04:33
24-Jul-2009 04:33
If you are going to use foreach after explode(), call reset() before foreach:
<?php
$arr = explode("\n", 'test \n test2 \n test3');
reset($arr);
foreach($arr as $line)
{ /* do something */ ; }
?>
marcus at synchromedia dot co dot uk
15-Jun-2009 03:50
15-Jun-2009 03:50
Just in case the comment about empty strings is not clear:
<?php
$a = array();
var_dump($a);
$s = implode("\n", $a);
var_dump($s);
$b = explode("\n", $s);
var_dump($b);
$b = preg_split('/\n/', $s,-1,PREG_SPLIT_NO_EMPTY);
var_dump($b);
?>
Results in:
array(0) {
}
string(0) ""
array(1) {
[0]=>
string(0) ""
}
array(0) {
}
i.e. exploding an empty string results in an array with one element. You can use preg_split to skip the empty item, but that may not be quite what you need should your array have empty elements intentionally.
SR
21-Apr-2009 04:50
21-Apr-2009 04:50
Keep in mind that explode() can return empty elements if the delimiter is immediately repeated twice (or more), as shown by the following example:
<?php
$foo = 'uno dos tres'; // two spaces between "dos" and "tres"
print_r(explode(' ', $foo));
?>
Array
(
[0] => uno
[1] => dos
[2] =>
[3] => tres
)
Needless to say this is definitely not intuitive and must be handled carefully.
Michael
19-Apr-2009 11:29
19-Apr-2009 11:29
Here's a simple script which uses explode() to check to see if an IP address is in an array (can be used as a ban-check, without needing to resort to database storage and queries).
<?php
function denied($one) {
$denied = array(
0 => '^255.255.255.255',
1 => '^255.250',
2 => '^255.255.250'
);
for ($i = 0 ; $i < sizeof($denied) ; $i++) {
if (sizeof(explode($denied[$i], '^' . $one . '$')) == 2) {
return true;
}
}
return false;
}
if (denied($_SERVER['REMOTE_ADDR'])) {
header('Location: denied.php');
}
?>
Navi
31-Mar-2009 02:03
31-Mar-2009 02:03
<?php
function my_explode($delim, $str, $lim = 1)
{
if ($lim > -2) return explode($delim, $str, abs($lim));
$lim = -$lim;
$out = explode($delim, $str);
if ($lim >= count($out)) return $out;
$out = array_chunk($out, count($out) - $lim + 1);
return array_merge(array(implode($delim, $out[0])), $out[1]);
}
?>
This function can assume `limit' parameter less than 0, for example:
<?php
print_r(my_explode('.', 'file.some.ext.jpg', -2));
?>
prints
Array
(
[0] => file.some.ext
[1] => jpg
)
adrian at bilsoftware dot com
23-Feb-2009 11:40
23-Feb-2009 11:40
<?php
function explode_escaped($delimiter, $string){
$exploded = explode($delimiter, $string);
$fixed = array();
for($k = 0, $l = count($exploded); $k < $l; ++$k){
if($exploded[$k][strlen($exploded[$k]) - 1] == '\\') {
if($k + 1 >= $l) {
$fixed[] = trim($exploded[$k]);
break;
}
$exploded[$k][strlen($exploded[$k]) - 1] = $delimiter;
$exploded[$k] .= $exploded[$k + 1];
array_splice($exploded, $k + 1, 1);
--$l;
--$k;
} else $fixed[] = trim($exploded[$k]);
}
return $fixed;
}
?>
Here's a function which explodes string with delimiter, but if delimiter is "escaped" by backslash, function won't split in that point. Example:
<?php
$result = explode_escaped(',', 'string, piece, group\, item\, item2, next\,asd');
print_r($result);
?>
Will give:
Array
(
[0] => string
[1] => piece
[2] => group, item, item2
[3] => next,asd
)
Elad Elrom
05-Dec-2008 06:02
05-Dec-2008 06:02
<?php
// Remove words if more than max allowed character are insert or add a string in case less than min are displayed
// Example: LimitText("The red dog ran out of thefence",15,20,"<br>");
function LimitText($Text,$Min,$Max,$MinAddChar) {
if (strlen($Text) < $Min) {
$Limit = $Min-strlen($Text);
$Text .= $MinAddChar;
}
elseif (strlen($Text) >= $Max) {
$words = explode(" ", $Text);
$check=1;
while (strlen($Text) >= $Max) {
$c=count($words)-$check;
$Text=substr($Text,0,(strlen($words[$c])+1)*(-1));
$check++;
}
}
return $Text;
}
?>
Nobody
17-Nov-2008 02:38
17-Nov-2008 02:38
A really better and shorter way to get extension is via:
<?php $extension = end(explode('.', $filename)); ?>
this will print the last part after the last dot :)
shaun
29-Aug-2008 09:24
29-Aug-2008 09:24
For anyone trying to get an array of key => value pairs from a query string, use parse_str. (Better alternative than the explode_assoc function listed way down the page unless you need different separators.)
pinkgothic at gmail dot com
15-Oct-2007 11:26
15-Oct-2007 11:26
coroa at cosmo-genics dot com mentioned using preg_split() instead of explode() when you have multiple delimiters in your text and don't want your result array cluttered with empty elements. While that certainly works, it means you need to know your way around regular expressions... and, as it turns out, it is slower than its alternative. Specifically, you can cut execution time roughly in half if you use array_filter(explode(...)) instead.
Benchmarks (using 'too many spaces'):
Looped 100000 times:
preg_split: 1.61789011955 seconds
filter-explode: 0.916578054428 seconds
Looped 10000 times:
preg_split: 0.162719011307 seconds
filter-explode: 0.0918920040131 seconds
(The relation is, evidently, pretty linear.)
Note: Adding array_values() to the filter-explode combination, to avoid having those oft-feared 'holes' in your array, doesn't remove the benefit, either. (For scale - the '9' becomes a '11' in the benchmarks above.)
Also note: I haven't tested anything other than the example with spaces - since djogo_curl at yahoo's note seems to imply that explode() might get slow with longer delimiters, I expect this would be the case here, too.
I hope this helps someone. :)
seventoes at gmail dot com
10-Dec-2006 04:49
10-Dec-2006 04:49
Note that explode, split, and functions like it, can accept more than a single character for the delimiter.
<?php
$string = "Something--next--something else--next--one more";
print_r(explode('--next--',$string));
?>
djogo_curl at yahoo
01-Dec-2004 01:50
01-Dec-2004 01:50
Being a beginner in php but not so in Perl, I was used to split() instead of explode(). But as split() works with regexps it turned out to be much slower than explode(), when working with single characters.
coroa at cosmo-genics dot com
16-Nov-2003 05:01
16-Nov-2003 05:01
To split a string containing multiple seperators between elements rather use preg_split than explode:
preg_split ("/\s+/", "Here are to many spaces in between");
which gives you
array ("Here", "are", "to", "many", "spaces", "in", "between");