for
This is a really silly example of how you can implement foreach for objects in a really crazy way...
It's not something you should use...
<?php
/**
* Same as foreach, for objects...
*
* @param object|array $_collection
* @param callback $_lambda
* @param mixed $_data optional
* @return void
*/
function loop($_collection, $_lambda, $_data = null)
{
if(is_array($_collection))
{
foreach($_collection as $key => $value)
{
if(is_null($_data))
$_lambda($key, $value);
else
$_lambda($key, $value, $_data);
}
}
elseif(is_object($_collection))
{
$iter = $_collection->getIterator();
$iter->rewind();
while($iter->valid())
{
if(is_null($_data))
$_lambda($iter->key(), $iter->current());
else
$_lambda($iter->key(), $iter->current(), $_data);
$iter->next();
}
}
else
trigger_error('Only Accepts Objects or Arrays', E_USER_ERROR);
}
// and this is how to use it...
$data = "some random data"; // you can place $this here
loop(new ArrayObject(array(1,2,3,4)), function(&$_key, &$_value, &$_data)
{
echo $_key.$_value.$_data;
}, $data);
?>
foreach
PHP 4 introduced a foreach construct, much like Perl and some other languages. This simply gives an easy way to iterate over arrays. foreach works only on arrays, and will issue an error when you try to use it on a variable with a different data type or an uninitialized variable. There are two syntaxes; the second is a minor but useful extension of the first:
foreach (array_expression as $value)
statement
foreach (array_expression as $key => $value)
statement
The first form loops over the array given by array_expression. On each loop, the value of the current element is assigned to $value and the internal array pointer is advanced by one (so on the next loop, you'll be looking at the next element).
The second form does the same thing, except that the current element's key will be assigned to the variable $key on each loop.
As of PHP 5, it is possible to iterate objects too.
Note: When foreach first starts executing, the internal array pointer is automatically reset to the first element of the array. This means that you do not need to call reset() before a foreach loop.
Note: Unless the array is referenced, foreach operates on a copy of the specified array and not the array itself. foreach has some side effects on the array pointer. Don't rely on the array pointer during or after the foreach without resetting it.
As of PHP 5, you can easily modify array's elements by preceding $value with &. This will assign reference instead of copying the value.
<?php
$arr = array(1, 2, 3, 4);
foreach ($arr as &$value) {
$value = $value * 2;
}
// $arr is now array(2, 4, 6, 8)
unset($value); // break the reference with the last element
?>
This is possible only if iterated array can be referenced (i.e. is variable), that means the following code won't work:
<?php
foreach (array(1, 2, 3, 4) as &$value) {
$value = $value * 2;
}
?>
Warning
Reference of a $value and the last array element remain even after the foreach loop. It is recommended to destroy it by unset().
Note: foreach does not support the ability to suppress error messages using '@'.
You may have noticed that the following are functionally identical:
<?php
$arr = array("one", "two", "three");
reset($arr);
while (list(, $value) = each($arr)) {
echo "Value: $value<br />\n";
}
foreach ($arr as $value) {
echo "Value: $value<br />\n";
}
?>
The following are also functionally identical:
<?php
$arr = array("one", "two", "three");
reset($arr);
while (list($key, $value) = each($arr)) {
echo "Key: $key; Value: $value<br />\n";
}
foreach ($arr as $key => $value) {
echo "Key: $key; Value: $value<br />\n";
}
?>
Some more examples to demonstrate usages:
<?php
/* foreach example 1: value only */
$a = array(1, 2, 3, 17);
foreach ($a as $v) {
echo "Current value of \$a: $v.\n";
}
/* foreach example 2: value (with its manual access notation printed for illustration) */
$a = array(1, 2, 3, 17);
$i = 0; /* for illustrative purposes only */
foreach ($a as $v) {
echo "\$a[$i] => $v.\n";
$i++;
}
/* foreach example 3: key and value */
$a = array(
"one" => 1,
"two" => 2,
"three" => 3,
"seventeen" => 17
);
foreach ($a as $k => $v) {
echo "\$a[$k] => $v.\n";
}
/* foreach example 4: multi-dimensional arrays */
$a = array();
$a[0][0] = "a";
$a[0][1] = "b";
$a[1][0] = "y";
$a[1][1] = "z";
foreach ($a as $v1) {
foreach ($v1 as $v2) {
echo "$v2\n";
}
}
/* foreach example 5: dynamic arrays */
foreach (array(1, 2, 3, 4, 5) as $v) {
echo "$v\n";
}
?>
add a note
User Contributed Notesforeach
mazdak dot farrokhzad at piratpartiet dot se
23-Sep-2009 11:49
23-Sep-2009 11:49
s dot mattison at gmail dot filtersoutmyspam dot com
10-Sep-2009 05:19
10-Sep-2009 05:19
I hope other people find this useful.
<?php
/*
---------------------------------
"Null" Array filler
by Steve Mattison
This script shows one way PHP can
display an array, and pad it with
'nonexistant' values. This may be
useful, for instance, in reducing
the size of a database by storing
only values that deviate from a
set standard.
---------------------------------
*/
$arr = array(3, 5, -47); //the values. we're looking for the first two.
//an arbitrary lower number must append the array.
//this is so the main loop continues after the last value has been found.
$arr2 = array("oranges", "pears", null); //value descriptions.
foreach ($arr as $key=>$value) { //get next value that we seek.
for($iterate=$last+1;$iterate<10;$iterate++){ //iterate a loop.
//start at the last position+1, in case we've already looped once.
//if we haven't looped yet, $last is not defined; we start at 1.
$last=$iterate; //keep track of our position.
echo '<br>['.$iterate.'] - '; //show it.
if($iterate==$value){ //an array value has appeared.
echo ($arr2[$key]); //show the deviant value.
break; //break the loop and get the next value.
} //end if
else echo ("apples"); //otherwise show the default value.
} //next $iterate
//array values higher than the loop condition will be ignored.
//optionally, you may wish to check for this and display them here.
} //next-each $arr
unset($value); //clear up the memory used by foreach
//Example Result Set:
//[1] - apples
//[2] - apples
//[3] - oranges
//[4] - apples
//[5] - pears
//[6] - apples
//[7] - apples
//[8] - apples
//[9] - apples
?>
hueen
25-Aug-2009 01:15
25-Aug-2009 01:15
In addition to the previous post by Krzysztof:
The above manual states that "Reference of a $value and the last array element remain even after the foreach loop", but it should also be noted that foreach does not reinitialize $value _before_ iterating. This means that if $value is a reference (of anything) before a foreach($array as $value) loop, it will remain a reference while foreach is iterating (and thus the reference's target gets overwritten with each iteration). If that foreach is run by reference though (foreach($array as &$value)), $value's original reference inherently gets dropped and it references each current $array element instead (as expected).
Krzysztof - ksobolewski at o2 dot pl
09-Jul-2009 06:50
09-Jul-2009 06:50
The weird behaviour of references in foreach remains as long as in PHP 5.2.08 (Linux) and PHP 5.2.9 (Windows XP). The simplest example would be:
<?php
$a = array('a', 'b','c');
foreach($a as &$row){
//you don't have to do anything here
}
print_r($a);
foreach($a as $row){
echo "<br />".$row;
}
?>
the result of print_r will be correct - array of ('a','b','c') values. The second foreach, however, would
produce a,b,b. For all arrays, regardless of size, it would be the n-1 element
(the element right before the last one). Eg. for 'a','b','c','d','e','f', the script would produce a,b,c,d,e,e.
There are few solutions to this:
1. safest - avoid using references in foreach; so instead of
<?php
foreach($a as &$row){
// do something, eg.
$row = trim($row);
}
?>
you would use
<?php
foreach($a as $i=>$row){
// do something on row, eg.
$row = trim($row);
// replace the row in the table
$a[$i]=$row;
}
?>
decrease of performance is the cost, however
2. equally safe and more usable - unset the element reference right after the foreach loop with references, eg.:
<?php
$a = array('a', 'b','c');
foreach($a as &$row){
//you don't have to do anything here
}
unset ($row)); // it is safe now to use $row again
print_r($a);
foreach($a as $row){
echo "<br />".$row;
}
?>
3. use references in both case; it seems that iterations work correct if you use &$row in both loops or don't use it in any:
<?php
$a = array('a', 'b','c');
foreach($a as &$row){
//you don't have to do anything here
}
print_r($a);
// works OK now even without unset($row)
foreach($a as &$row){
echo "<br />".$row;
}
?>
4. use references in foreach only inside functions or methods; outside the function scope it should be safe
<?php
function cleanTable($a){
foreach($a as &$row){
$row = trim($row);
}
}
$a = array('a','b','c');
cleanTable($a);
foreach($a as $row){
echo "<br />".$row;
}
?>
drawbacks: NONE! I Quite contrary, the code looks more tidy.
5. avoid using the same variable names for referenced and non-referenced values; for example, in the first case use &$rRow, and in the second one - $row. It's neither elegant, nor efficient, though, as each new variable lowers the application performance a bit.
<?php
$a = array('a', 'b','c');
foreach($a as &$rRow){ // $rRow for 'referenced row'
//you don't have to do anything here
}
print_r($a);
foreach($a as $row){
echo "<br />".$row;
}
?>
burleigh at chorus dot net
04-May-2009 12:21
04-May-2009 12:21
Using numeric indexes doesn't automatically sort your array.
<?php
$titles[3] = 'three';
$titles[2] = 'two';
$titles[1] = 'one';
print_r( $titles);
foreach ($titles as $t ) {
print "title=$t ";
}
?>
will display:
Array ( [3] => three [2] => two [1] => one )
title=three title=two title=one
If you want the items coming out in the correct order you need to use sort
<?php
sort($titles);
print_r($titles);
?>
Array ( [0] => one [1] => three [2] => two )
grobemo
24-Apr-2009 01:13
24-Apr-2009 01:13
You may want to do something different on the last iteration through a foreach loop. For instance, if you're printing a series of HTML list elements, you may want to add a class like 'last' to the final <li> element.
I had trouble finding a good way to do this with a foreach loop. The following code illustrates the method I worked out.
<?php
$array = array('apples','bananas','cranberries','durians');
$last_item = end($array);
foreach($array as $item) {
if ($item == $last_item) {
print "I like to eat " . $item;
}
}
?>
The foreach loop outputs: 'I like to eat durians'.
Technically, you could just use if ($item == end($array)), but I assume that would require more processing time.
strata_ranger at hotmail dot com
19-Apr-2009 12:03
19-Apr-2009 12:03
Note that foreach() iterates through an array in the same order that its elements were defined. If you want to iterate through an array in a different order, you will need to sort the array prior to entering the loop.
For example:
<?php
// Iterate through an array in reverse order,
// maintaining key association (i.e. for associative arrays)
foreach(array_reverse($array, true) as $key=>$value)
{
. . .
}
?>
timgolding_10 at hotmail dot com
09-Apr-2009 04:50
09-Apr-2009 04:50
Here's an example where one can loop through two or more arrays in one loop. this example has two arrays.
<?php
$array1=array("a", "b", "c");
$array2=array("1", "2", "3");
foreach(array_merge($array1, $array2) as $value)
{
echo $value;
}
// abc123
?>
For more arrays just add them as additional arguments to the array_merge function. This example isn't very useful if your loop needs to return the keys for numeric indexed arrays. For associative arrays you can return the key however must be certain that all the indexes are unique across all arrays.
tedivm at tedivm dot com
29-Jan-2009 04:44
29-Jan-2009 04:44
foreach and the while/list/each methods are not completely identical, and there are occasions where one way is beneficial over the other.
<?php
$arr = array(1,2,3,4,5,6,7,8,9);
foreach($arr as $key=>$value)
{
unset($arr[$key + 1]);
echo $value . PHP_EOL;
}
?>
Output:
1 2 3 4 5 6 7 8 9
<?php
$arr = array(1,2,3,4,5,6,7,8,9);
while (list($key, $value) = each($arr))
{
unset($arr[$key + 1]);
echo $value . PHP_EOL;
}
?>
Output:
1 3 5 7 9
[EDIT BY danbrown AT php DOT net: Contains a typofix by (scissor AT phplabs DOT pl) on 30-JAN-2009.]
zodiac2800 at msn dot com
06-Nov-2008 11:36
06-Nov-2008 11:36
Here is a way to declare global variable variables using a function.
This particular example handles an array that contains names of $_POST items. This is to avoid the notices that php gives when checking an unused $_POST.
<?php
function check ($inputs) {
foreach ($inputs as $input) {
global $$input;
$$input = isset($_POST[$input]) ? $_POST[$input] : "";
}
}
?>
Robin Leffmann
25-Sep-2008 08:51
25-Sep-2008 08:51
It should be noted that when using foreach to pass an array's key ($key => $value), the key must be a string and not binary content - containing 0's, f.e., as was my case when i used foreach to parse bencoded data handed back to me from a bittorrent tracker scraping - as this will throw foreach off and hand you a key that is binary different than the actual content of the array.
rhi
17-Sep-2008 05:22
17-Sep-2008 05:22
If you use foreach with references, don't forget to unset the reference if you are not sure that a later piece of code doesn't use the same variable name. Example:
<?php
$latest_tutorials = $db->queryAll("select * from tutorials"...);
foreach ($latest_tutorials as &$tut)
$tut["comments"] = $db->queryOne("select count(*) ...");
// ...
$tut = $db->queryRow("...");
print_tutorials($latest_tutorials);
print_tutorial($tut);
?>
Here the last entry of latest_tutorials will be replaced by the row that is fetched by the $tut = $db->queryRow("..."); line because $tut is still referencing the last array entry. Solution:
<?php
foreach ($latest_tutorials as &$tut)
$tut["comments"] = $db->queryOne("select count(*) ...");
unset($tut);
// ...
$tut = $db->queryRow("...");
?>
brian at diamondsea dot com
15-Aug-2008 10:15
15-Aug-2008 10:15
A common problem is having PHP generate an error when trying to iterate through an array that may sometimes have no data in it. This causes PHP to generate a warning such as:
Warning: Invalid argument supplied for foreach() in test.php on line 14
You can prevent this error by type-casting the foreach variable as an array type using "(array)" before the array variable name.
<?php
// double any value whose key starts with 'b'
$arr = array('a'=>1, 'b1'=>2, 'b2'=>3, 'c'=>4, 'd'=>5);
$non_array = null;
// Normal usage with an array
print "Test 1:\n";
foreach ($arr as $key => $val) {
print "Key $key, Value $val\n";
}
// Normal usage with a non-array (undefined or otherwise empty data set)
// Outputs: Warning: Invalid argument supplied for foreach() in test.php on line 16
print "Test 2:\n";
foreach ($non_array as $key => $val) {
print "Key $key, Value $val\n";
}
// By casting the $non_array to an (array) type, it will function without error, skipping the loop
print "Test 3:\n";
foreach ((array) $non_array as $key => $val) {
print "Key $key, Value $val\n";
}
print "Done.\n";
?>
Outputs:
Test 1:
Key a, Value 1
Key b1, Value 2
Key b2, Value 3
Key c, Value 4
Key d, Value 5
Test 2:
Warning: Invalid argument supplied for foreach() in /home/bgallagher/test.php on line 16
Test 3:
Done.
adam dot sindelar at gmail dot com
14-Apr-2008 08:45
14-Apr-2008 08:45
You can also use the alternative syntax for the foreach cycle:
<?php
foreach($array as $element):
#do something
endforeach;
?>
Just thought it worth mentioning.
marian at devourmedia dot com
28-Feb-2008 07:34
28-Feb-2008 07:34
Also, do not forget that foreach is not useful
if you change the value inside of the loop.
For example:
<?php
$t=array('a', 'a', 'a', 'a', 'a', 'a', 'a', '1', 'a', 'a', 'a', 'a', 'a');
foreach($t as $var=>$val)
{
$t=array();
echo "val={$val}<br>";
}
?>
is still showing the contents of the array $t.
henrik at newdawn dot dk
27-Oct-2007 05:08
27-Oct-2007 05:08
As stated further up the foreach is consuming a lot of memory if used within large arrays - that is - if the array consists of for instance large objects. I had a case where a foreach caused me to run out of the 256 MB memory that PHP is allowed to handle - but changing to a for() statement completly removed both memory and CPU load.
tcrosby at gmail dot com
27-Aug-2007 08:37
27-Aug-2007 08:37
Using the much-maligned ability of foreach to work on references rather than copies, it becomes possible to recurse indefinitely into deep arrays without the need to know beforehand how deep they go. Consider the following example (which I use to sanitize input):
<?php
// Sanitize as a function to allow recursing; original array passed by reference
function sanitize(&$array) {
foreach ($array as &$data) {
if (!is_array($data)) { // If it's not an array, clean it
$data = '\\' . $data; // addslashes(), mysql_real_escape_string() or whatever you wish to use, this is merely a simple example
}
else { // If it IS an array, call the function on it
sanitize($data);
}
}
}
// Test case
$test = array(
array(
array(
0,
1,
2
),
3,
4
),
5,
6
);
// Output
sanitize($test);
print_r($test);
/*
Output:
Array
(
[0] => Array
(
[0] => Array
(
[0] => \0
[1] => \1
[2] => \2
)
[1] => \3
[2] => \4
)
[1] => \5
[2] => \6
)
*/
?>
When first called on $test, it passes a reference to the original $test array to the sanitize function, which begins to iterate through its contents with the immediate foreach loop. Each value that is not in itself an array gets sanitized as normal, and as both the foreach loop and the function itself are acting by reference, all changes happen directly to the contents of the superglobal rather than to copies. If the value given IS an array, it then calls the same function on it. The key here is that both the function and the foreach loop work by reference, meaning that you can call the calling function while in the foreach loop and all changes are still applied to the original array, without corruption of the array pointer, as it remains intact for each level of the array. When the end of an array is reached, the function simply returns; if it was a deeper-level array, the parent function (and parent foreach loop) continue as they were; if the top-level loop ends, then the function returns to the main code, having acted on the entire array. As everything operates within the scope of the sanitize function, you even avoid the danger of leaving the last reference set, as $data is not available outside the scope of the function in which any particular loop operates. While this might sound complicated at first, the result is that by passing to foreach by reference, true indefinite recursion is possible.
Luke at chaoticlogic dot net
02-Jul-2007 03:08
02-Jul-2007 03:08
Alright, I had a little error. I had one foreach() declaration, and then another foreach() declaration.
They went:
<?php
//$connections is an array of Socket resources
foreach ($connections as $key => &$value) {
//the code here is impertinent
}
//$users is an associative array
foreach ($users as $key => &$value) {
//the code here is impertinent
}
?>
Alright, now, what error was produced as a result of this?
This one:
"Warning: Cannot use scalar value as array in filename.php on line 69."
I then realized something; the reason for this came from the fact that I used $key, and $value for both of them in the exact same way.
As a response to this, I've developed two ways to fix this:
<?php
//add this to the end of every foreach() you use
unset($key,$value)
?>
OR
Simply use different variables for each one.
27-Jan-2007 12:50
Here is an obvious question to most of the readers, but it took me about two precious minutes to figure out, so I figured I will share it will you:
What will be the output of the following statement:
<?php
$data = array('1' => 'field1', '2' => 'field2');
foreach ($data as $field_index => $field_name);
{
echo "$field_name";
}
?>
Correct answer is 'field2', and not 'field1field2'. The forgotten semicolon at the foreach line does not trigger a syntax error, but php treats it as an empty statement..
and then the block is run once with the last value set into $field_name.
Timon Van Overveldt
15-Jan-2007 10:41
15-Jan-2007 10:41
Why not just do this?
<?php
$arr = array(1, 2, 3, 4);
foreach ($arr as $i => $value) {
$arr[$i] = $value * 2;
}
// $arr is now array(2, 4, 6, 8)
?>
No need for references, so it works in both PHP4 and PHP5.
simplex
19-Dec-2006 02:12
19-Dec-2006 02:12
"As of PHP 5, you can easily modify array's elements by preceding $value with &. This will assign reference instead of copying the value."
There are cases where array_walk or array_map are inadequate (conditional required) or you're just too lazy to write a function and pass values to it for use with array_map...
My solution to foreach for php 4 and 5 to modify values of an array directly:
<?php
$testarr = array("a" => 1, "b" => 2, "c" => 3, "d" => 4);
$testarr_keys = array_keys($testarr);
$testarr_values = array_values($testarr);
for ($i = 0; $i <= count($testarr) - 1; $i++) {
$testarr[$testarr_keys[$i]] = $testarr_values[$i] * 2;
}
print_r($testarr);
?>
robycar at libero dot com
07-Dec-2006 01:04
07-Dec-2006 01:04
some useful functions for testing boolean values
<?php
$trueValues = array('1', 'true', 't', 'y', 'yes', 'vero', 'v'); //edit with locale values
$falseValues = array('0', 'false', 'f', 'n', 'no', 'falso'); //edit with locale values
function str_to_bool($str) {
foreach ($GLOBALS['trueValues'] as $value)
if (strcasecmp($str, $value) == 0)
return true;
foreach ($GLOBALS['falseValues'] as $value)
if (strcasecmp($str, $value) == 0)
return false;
return NULL;
}
function str_is_true($str) {
return (str_to_bool($str) === true);
}
function str_is_false($str) {
return str_to_bool($str) === false;
}
/* Test */
str_to_bool('false'); //return false
str_to_bool('vero'); // return true
str_to_bool('php'); //return null
str_is_true('php'); //return false
str_is_false('php'); //return false
?>
gherson
30-May-2006 02:33
30-May-2006 02:33
To "foreach" over the characters of a string, first "preg_split" the string into an array:
<?php
$string="string";
$array = preg_split('//', $string, -1, PREG_SPLIT_NO_EMPTY);
foreach($array as $char) print($char."<br/>");
?>
This outputs:
s
t
r
i
n
g
Edwin_fromUtrecht at NOSPAM dot example dot com
15-Feb-2006 08:39
15-Feb-2006 08:39
To comment on the foreach statement behaviour comment below: The reason for this different behaviour is that the foreach statement is equivalent to the each statement. They both make use of an internal pointer. To loop through the complete array after a change you could use the reset statement on the array.
daniel dot oconnor at gmail dot com
09-Feb-2006 12:42
09-Feb-2006 12:42
Dangers with References
<?php
$months = array("Jan", "Feb", "March");
foreach ($months as &$month) {
$month .= "Beep";
}
print_r($months);
foreach ($months as $month) {
printf("%s\n", $month);
}
?>
Because $month is a reference to $months[2], iterating again with the same varible name causes $months[2] to be overwritten! Oh no!
Ouput:
Array
(
[0] => JanBeep
[1] => FebBeep
[2] => MarchBeep
)
JanBeep
FebBeep
FebBeep
RabidDog
17-Jan-2006 04:17
17-Jan-2006 04:17
Pretty weird but for future reference
<?php
//doesn't multiply the last value
foreach ($ar as &$v){
$v *= 2;
}
foreach($ar as $v){
echo $v. "<br>";
}
//works fine
foreach ($ar as &$o){
$o *= 2;
}
foreach($ar as $v){
echo $v. "<br>";
}
?>
janezr at jcn dot si
10-Nov-2005 03:06
10-Nov-2005 03:06
If you want to "look-ahead" values in an associative or non-continuous array, this might help:
<?php
$myArray = {'one'=>1,'two'=>2,'five'=>5,'three'=>3}
$all_keys = array_keys($myArray);
foreach ( $all_keys as $key_index => $key ) {
$value =& $myArray[$key];
// $all_keys[$key_index+2] gives null if we go past the array boundary - be carefull there
$value2 =& $myArray[$all_keys[$key_index+2]] ;
...
}
?>
mikeb at tracersinfo dot com
26-Jul-2005 12:18
26-Jul-2005 12:18
Using PHP5's foreach "as reference" can bite you!
Three guys in my office spent about a day chasing this one's tail, that was causing aberrant behavior in the values of elements of an array. It turns out to be a consequence of the nature of references, generally.
If you create a reference to a variable, all names for that variable (including the original) BECOME REFERENCES. To paraphrase "The Highlander," if you want a name to OWN a piece of data, "there can be only one."
To illustrate this point, consider the following code:
<?php
$f = array(
0 => array('value' => 'three'),
1 => array('value' => 'three')
);
foreach ( $f as $k => &$v ) {
$v['value'] = 'one';
}
$a = $f;
$b = $f;
$b[0]['value'] = 'two';
$b[1]['value'] = 'two';
var_dump($a, $b);
?>
Upon execution, you will find that, although you would expect $a to contain two arrays with 'value' of 'one', $a and $b are identical -- i.e., the changes of []['value'] to 'two' have happened in both arrays. But, upon further examination of the var_dumps, you will see that both sets' elements [0] and [1] are preceded with "&": they are references!
The easy solution to this problem turns out to be: unset the foreach "as-reference" variable ($v) at the bottom of your foreach loop. This allows the original variable (or array member) to resume ownership of the value and dissolves its "reference-ness".
magistrata at gmail dot com
13-Jul-2005 11:59
13-Jul-2005 11:59
I use this code to do a simple cleanup on information heading from an HTML form into a database:
<?php
foreach ($_POST as $key => $value) {
$$key = addslashes(trim($value));
}
?>
barnacle83-phpnotes at yahoo dot com
30-Jun-2005 03:06
30-Jun-2005 03:06
Here are various ways I've seen to iterate arrays by reference in PHP4.
Based on my tests, I have placed them in order of fastest to slowest.
Benchmarking tool I used:
http://phplens.com/phpeverywhere/phpe-2004.htm#a3297
http://phplens.com/lens/dl/JPBS.zip
<?php
// --------------------------------------------------------------------
foreach ( array_keys($myArray) as $key ) {
$element =& $myArray[$key];
...
}
// --------------------------------------------------------------------
foreach( $myArray as $key => $element ) {
$element =& $myArray[$key];
...
unset($element);
}
// --------------------------------------------------------------------
reset($myArray);
while ( list($key) = each($myArray) ) {
$element =& $myArray[$key];
...
unset($element);
}
?>
Andrew
30-May-2005 12:17
How To Use References In Foreach Safely And Sanely In PHP 4.
There are two really really important points to remember about foreach and references:
1. foreach makes a copy
2. references (and unset!) work by directly manipulating the symbol table
In practice, this means that if you have an array of objects (or arrays) and you need to work on them *in-place* in a foreach loop, you have to do this:
<?php
foreach( $object_list as $id => $the_object ) {
$the_object = & $object_list[$id]; // Re-assign the variable to point to the real object
....
unset($the_object); // Break the link to the object so that foreach doesn't copy the next one on top of it.
}
?>
This really works. I have used it in dozens of places. Yes, you need it all, including the unset(). You will get extremely hard-to-find bugs if you leave out the unset().
Static.
flobee at gmail dot com
21-May-2005 03:32
21-May-2005 03:32
be aware! take the note in the manual serious: "foreach operates on a copy of the specified array"
when working with complex systems you may get memory problems because of all this copies of arrays.
i love this function (easy to use) and use it more often than "for" or "while" functions but now i have really problems on this and finally found the reason (which can be a mess to find out)!
the sum of memory usage sometimes can be *2 than you really need.
Paul Chateau
17-May-2005 01:01
17-May-2005 01:01
I had the same problem with foreach() and a recursiv function. If you don't want to spend about 1 or 2 hours to solve this problem, just use for() loops instead of foreach().
Some Example:
<?php
$arr[] = array(1,"item1");
$arr[] = array(2,"item2");
$arr[] = array(1,"item3");
//$arr[] = ...
//doesn't work
function foo($x) {
global $arr; // some Array
foreach($arr as $value) {
if($value[0] == $x) {
echo $value[1]."\n";
foo($value[0]);
}
}
}
//just use this
function foo($x) {
global $arr; // some Array
for($i=0; $i < count($arr); $i++) {
if($arr[$i][0] == $x) {
echo $arr[$i][1]."\n";
foo($arr[$i][0]);
}
}
}
?>
Paul
gardan at gmx dot de
07-Oct-2004 02:21
07-Oct-2004 02:21
(PHP 5.0.2)
Pay attention if using the same variable for $value in both referenced and unreferenced loops.
<?php
$arr = array(1 => array(1, 2), 2 => array(1, 2), 3 => array(1, 2));
foreach($arr as &$value) { }
foreach(array(1,2,3,4,5) as $value) { }
echo $test[3];
?>
What happens here is that after the first foreach() loop, you have in $value a reference to the last element of $arr (here: array(1, 2)).
Upon entering the second foreach(), php assigns the value. Now value is assigned to where $value (which is still a reference) points, that is, the last element of $arr.
Your output will be "5", not the expected "Array". To be on the safe side, unset($value) before entering the next foreach().
scott at slerman dot net
17-Apr-2004 10:27
17-Apr-2004 10:27
Apparently the behavior of foreach with classes changed in PHP5. Normally, foreach operates on a copy of the array. If you have something like
<?php
foreach ($array as $value){
$value = "foo";
}
?>
the original array will not be modified. However, testing this code on PHP5RC1
<?php
class foobar {
var $a;
var $b;
function foobar(){
$this->a = "foo";
$this->b = "bar";
}
}
$a = new foobar;
$b = new foobar;
$c = new foobar;
$arr = array('a' => $a, 'b' => $b, 'c' => $c);
foreach ($arr as $e){
$e->a = 'bah';
$e->b = 'blah';
}
var_dump($arr);
?>
resulted in the following output:
array(3) {
["a"]=>
object(foobar)#1 (2) {
["a"]=>
string(3) "bah"
["b"]=>
string(4) "blah"
}
["b"]=>
object(foobar)#2 (2) {
["a"]=>
string(3) "bah"
["b"]=>
string(4) "blah"
}
["c"]=>
object(foobar)#3 (2) {
["a"]=>
string(3) "bah"
["b"]=>
string(4) "blah"
}
}
It would seem that classes are actually passed by reference in foreach, or at least that methods are called on the original objects.
jazfresh at hotmail dot com
18-Feb-2004 12:50
18-Feb-2004 12:50
There is a really really big pitfall to watch out for if you are using "foreach" and references.
Recall this example:
<?php
$a = "Hello";
$b =& $a; // $b now refers to "Hello"
$b = "Goodbye"; // BOTH $a and $b now refer to "Goodbye"
?>
This also applies to the loop variable in a foreach construct. This can be a problem if the loop variable has already been defined as a reference to something else.
For example:
<?php
// Create some objects and store them in an array
$my_objects = array();
for($a = 0; $a < $num_objects; $a++) {
$obj =& new MyObject();
$obj->doSomething();
$my_objects[] =& $obj;
}
// later on in the same function...
foreach($my_objects as $obj) { // Note that we are trying to re-use $obj as the loop variable
$obj->doSomethingElse();
}
?>
When the "for" loop exits, $obj is a reference to the last MyObject that was created, which is also the last element in the "my_objects" array.
On every iteration, the foreach loop will do the equivalent of:
<?php
$obj = $my_objects[$internal_counter++];
?>
$obj will now refer to the appropriate element in the array.
But recall the reference example at the top. Because $obj was already defined as a reference, any assignment to $obj will overwrite what $obj was referring to. So in other words, on every foreach loop iteration, the last element in the array will be overwritten with the current array element.
To avoid this problem, either use a differently named loop variable, or call "unset()" on the loop variable before you begin the foreach().
It would be more intuitive PHP unset() the loop variable before a foreach began, maybe they'll put that in a later version.
andy at barbigerous dot net
06-Feb-2004 12:05
06-Feb-2004 12:05
For dual iteration, the internal pointers may need resetting if they've been previously used in a foreach.
<?PHP
for(
$someArray1.reset(),
$someArray2.reset();
list(, $someValue1 ) = each( $someArray1 ) ,
list(, $someValue2 ) = each( $someArray2 )
;
) {
echo $someValue1;
echo $someValue2;
}
?>
php at electricsurfer dot com
22-Apr-2003 03:33
22-Apr-2003 03:33
[Ed Note: You can also use array_keys() so that you don't have to have the $value_copy variable --alindeman at php.net]
I use the following to modify the original values of the array:
<?php
foreach ($array as $key=>$value_copy)
{
$value =& $array[$key];
// ...
$value = 'New Value';
}
?>
ian at NO_SPAM dot verteron dot net
01-Jan-2003 05:29
01-Jan-2003 05:29
Note that foreach is faster than while! If you can replace the following:
<?php
reset($array);
while(list($key, $val) = each($array))
{
$array[$key] = $val + 1;
}
?>
...with this (although there are functional differences, but for many purposes this replacement will behave the same way)...
<?php
foreach($array as $key => $val)
{
$array[$key] = $val + 1;
}
?>
You will notice about 30% - 40% speed increase over many iterations. Might be important for those ultra-tight loops :)
17-Sep-2002 11:06
"Also note that foreach operates on a copy of the specified array, not the array itself, therefore the array pointer is not modified as with the each() construct and changes to the array element returned are not reflected in the original array."
In other words, this will work (not too expected):
<?php
foreach ($array as $array) {
// ...
}
?>
While this won't:
<?php
while (list(, $array) = each($array)) {
// ...
}
?>