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 — 문자열을 문자열로 나눕니다
설명
array explode
( string $delimiter
, string $string
[, int $limit
] )
delimiter 문자열을 경계로 나누어진 string 의 부분 문자열로 이루어지는 배열을 반환합니다.
인수
- delimiter
-
경계 문자열.
- string
-
입력 문자열.
- limit
-
limit 를 지정하면, 반환하는 배열은 최대 limit 개의 원소를 가지고, 마지막 원소는 남은 string 모두를 포함합니다.
limit 인수가 음수이면, 마지막 -limit 를 제외한 모든 구성요소를 반환합니다.
implode()는 관습으로 인해 인수의 순서를 바꿀 수 있지만, explode()는 바꿀 수 없습니다. 반드시 delimiter 인수가 string 인수 앞에 위치해야 합니다.
반환값
delimiter 가 빈 문자열("")이면, explode()은 FALSE를 반환합니다. delimiter 가 string 에 존재하지 않으면, explode()는 string 을 포함하는 배열을 반환합니다.
변경점
| 버전 | 설명 |
|---|---|
| 5.1.0 | 음수 limit 지원 추가 |
| 4.0.1 | limit 인수 추가 |
예제
Example #1 explode() 예제
<?php
// 예제 1
$pizza = "piece1 piece2 piece3 piece4 piece5 piece6";
$pieces = explode (" ", $pizza);
echo $pieces[0]; // piece1
echo $pieces[1]; // piece2
// 예제 2
$data = "foo:*:1023:1000::/home/foo:/bin/sh";
list($user, $pass, $uid, $gid, $gecos, $home, $shell) = explode(":", $data);
echo $user; // foo
echo $pass; // *
?>
Example #2 limit 인수 예제
<?php
$str = 'one|two|three|four';
// 양수 limit
print_r(explode('|', $str, 2));
// 음수 limit (PHP 5.1부터)
print_r(explode('|', $str, -1));
?>
위 예제의 출력:
Array
(
[0] => one
[1] => two|three|four
)
Array
(
[0] => one
[1] => two
[2] => three
)
주의
Note: 이 함수는 바이너리 안전입니다.
참고
- preg_split() - 정규 표현식에 따라 문자열을 나눔
- str_split() - 문자열을 배열로 변환
- str_word_count() - 문자열에서 사용한 단어에 대한 정보를 반환
- strtok() - 문자열을 토큰화
- implode() - 문자열로 배열 원소를 결합
add a note
User Contributed Notesexplode
nick dot brown at free dot fr
15-Oct-2009 07:47
15-Oct-2009 07:47
Jrg Wagner
13-Oct-2009 06:28
13-Oct-2009 06:28
Here is a very concise example for a quote aware explode - substrings in quotes (or another definable enclosure char) are not exploded.
An additional parameter allows to determine whether the enclosure chars should be preserved within the resulting array elements. Please note that as of PHP 5.3 the str_getcsv function offers a built-in way to do this!
<?php
function csv_explode($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 07:20
29-Sep-2009 07:20
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 $key_arr;
}
?>
Anonymous
03-Sep-2009 11:18
03-Sep-2009 11:18
<?php
// converts pure string into a trimmed keyed array
function string2KeyedArray($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] => $a
[c] => 45%
[1] => true
[d] => ab c
)
Anonymous
11-Aug-2009 02:55
11-Aug-2009 02:55
If you are exploding string literals in your code that have a dollar sign ($) 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 11:33
24-Jul-2009 11:33
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 10:50
15-Jun-2009 10:50
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 11:50
21-Apr-2009 11:50
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(' ', $foo));
?>
Array
(
[0] => uno
[1] => dos
[2] =>
[3] => tres
)
Needless to say this is definitely not intuitive and must be handled carefully.
Michael
19-Apr-2009 06:29
19-Apr-2009 06:29
Here's a simple script which uses explode() to check to see if an IP address is in an array (can be used as a ban-check, without needing to resort to database storage and queries).
<?php
function denied($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($_SERVER['REMOTE_ADDR'])) {
header('Location: denied.php');
}
?>
Navi
31-Mar-2009 09:03
31-Mar-2009 09:03
<?php
function my_explode($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])), $out[1]);
}
?>
This function can assume `limit' parameter less than 0, for example:
<?php
print_r(my_explode('.', 'file.some.ext.jpg', -2));
?>
prints
Array
(
[0] => file.some.ext
[1] => jpg
)
adrian at bilsoftware dot com
24-Feb-2009 07:40
24-Feb-2009 07:40
<?php
function explode_escaped($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 02:02
05-Dec-2008 02:02
<?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 10:38
17-Nov-2008 10:38
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
30-Aug-2008 04:24
30-Aug-2008 04:24
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 06:26
15-Oct-2007 06:26
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 12:49
10-Dec-2006 12:49
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 09:50
01-Dec-2004 09:50
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
17-Nov-2003 01:01
17-Nov-2003 01:01
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");