PHP 手册
后退章 16. 流程控制前进


foreach

PHP 4 引入了 foreach 结构，和 Perl 以及其他语言很像。这只是一种遍历数组简便方法。foreach 仅能用于数组，当试图将其用于其它数据类型或者一个未初始化的变量时会产生错误。有两种语法，第二种比较次要但却是第一种的有用的扩展。 

foreach (array_expression as $value)
    statement
foreach (array_expression as $key => $value)
    statement

第一种格式遍历给定的 array_expression 数组。每次循环中，当前单元的值被赋给 $value 并且数组内部的指针向前移一步（因此下一次循环中将会得到下一个单元）。

第二种格式做同样的事，只除了当前单元的键名也会在每次循环中被赋给变量 $key。

自PHP 5 起，还可能遍历对象。

注: 当 foreach 开始执行时，数组内部的指针会自动指向第一个单元。这意味着不需要在 foreach 循环之前调用 reset()。

注: 除非数组是被引用，foreach 所操作的是指定数组的一个拷贝，而不是该数组本身。因此数组指针不会被 each() 结构改变，对返回的数组单元的修改也不会影响原数组。不过原数组的内部指针的确在处理数组的过程中向前移动了。假定 foreach 循环运行到结束，原数组的内部指针将指向数组的结尾。

自 PHP 5 起，可以很容易地通过在 $value 之前加上 & 来修改数组的单元。此方法将以引用赋值而不是拷贝一个值。

<?php
$arr = array(1, 2, 3, 4);
foreach ($arr as &$value) {
    $value = $value * 2;
}
// $arr is now array(2, 4, 6, 8)
?>

此方法仅在被遍历的数组可以被引用时才可用（例如是个变量）。

注: foreach 不支持用“@”来抑制错误信息的能力。

用户可能注意到了以下的代码功能完全相同：

<?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";
}
?>

以下代码功能也完全相同：

<?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";
}
?>

示范用法的更多例子：

<?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 key 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 add a note User Contributed Notes
gherson
31-May-2006 03:33
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
php at kormoc dot com
12-May-2006 02:25
With foreach and references, there is a super easy way to corrupt your data

see this test script:
<?php
$array = array(1,2,3);
foreach( $array as &$item );
foreach( $array as $item );
print_r( $array );
?>

You would imagine that it would have 1,2,3 but in reality, it outputs 1,2,2

The issue is that $item is a pointer to the last array value, and exists outside of the scope of the foreach, so the second foreach overwrites the value. If you would check what it gets set to in the second foreach loop, you would see that it gets set to 1 and then 2 and then 2 again.

This has already been filed as a bug, see:
http://bugs.php.net/bug.php?id=29992

but php developers seem to think that it's expected behaviour and *good* behaviour, so it's doubtful that it will change anytime soon. This is a really bad gotcha, so watch out.
php_man_resp at earthshod dot co dot uk
09-Mar-2006 11:58
To atroxodisse:  This behaviour is normal.  PHP arrays are associative arrays but, unlike Perl, with artificial order maintenance.  Keys can be any scalar value except references; of course integers are scalars, so traditional integer-indexed arrays just work.  {You can even have fractions in array indices, as long as you enclose the index in speech marks, such as $array["1.5"]!  This is not unique to PHP, by the way, but existed by accident in some dialects of BASIC seen on 1980s-vintage home computers.}  The foreach loop iterates over keys in chronological order of when they were added to the array, which is *not* necessarily the same as the sort order.  The print_r() function uses the same iteration order.

If you want to add elements to the beginning of an existing numeric array  {or between existing elements -- either using fractional indices, or because you left gaps when populating the array}  and have foreach iterate over them in order, then you will need to use ksort() on the array *first*.
Wout (BE)
24-Feb-2006 09:46
If you want to use an array, depending on a variable, you can point to it within a foreach function like this :

$language = EN;

$xyz_EN = array (...);

$xyz_NL = array (...);

foreach ( ${'xyz_'.$language} as ...)
{
  ...
};
Hermann
22-Feb-2006 09:55
foreach may be used not only to iterate through array elements, but also to iterate through object properties.

Documentation should specify that.
Edwin_fromUtrecht at NOSPAM dot example dot com
15-Feb-2006 10:39
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.
atroxodisse at gmail dot com
10-Feb-2006 09:04
I just noticed something.  I created an array, Looped through a mysql result with a while and added values to that array with an index that I incremented manually, starting at position 1.  After closing the while loop I added an element at position 0 of the array.  When I looped through that array with a foreach loop it evaluated the elements starting from the first element that was added instead of starting at position 0.  I'm not sure if that was intentional but it does not seem to be in the documentation.  So in this case looping through the array with a foreach was not the same as looping through it with a for loop like this:

for($i =0; $i<count($myarray); $i++)

To anyone coming from a C or C++ background this might be confusing.
daniel dot oconnor at gmail dot com
09-Feb-2006 02:42
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
egingell at sisna dot com
01-Feb-2006 01:26
That is definitely weird.

Anyway, I found out that if you put something like $ary[] in where either the key and/or the value goes, you'll append all the keys and/or values to that array. Example:

<?php

$array = array(
     'num1' => 'a',
     'num2' => 'b',
     'num3' => 'c'
);

$k = array();
$v = array();

foreach ($array as $k[] => $v[]);

echo '$k => ' . print_r($k, true);
echo '$v => ' . print_r($v, true);

?>

The above code will do this:

$k => Array (
     [0] => num1
     [1] => num2
     [2] => num3
)
$v => Array (
     [0] => a
     [1] => b
     [2] => c
)
RabidDog
17-Jan-2006 06:17
Pretty weird but for future reference

//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>"; 
}
pinheirosp at hotmail dot com
27-Dec-2005 12:25
In reply to FatalError, if you use Zend Dev Studio, i'll notice it's report "while(list() = each())" calls as "Using While w/ arrays param". So far, it's may be ambiguous to make things like that.

Prefer to make a clean code and use PHP "kernel" functions to navigate through an array.

Btw, if we take the exec time as example:

//a litte array, just to test =-]
$arr = array();
for($i=0; $i<100000; $i++) $arr[$i] = $i;

//list-each solution
$myTime = microtime(true);
reset($arr);
while (list($key, $value) = each($arr)) {
   $value = ($key * $value);
}
$myTime = microtime(true) - $myTime;
echo("list-each : " . $myTime . "<BR />\n");

//foreach solution
$myTime = microtime(true);
foreach ($arr as $key => $value) {
   $value = ($key * $value);
}
$myTime = microtime(true) - $myTime;
echo("foreach : " . $myTime . "<BR />\n");

/*
output:

list-each : 0.40198588371277
foreach : 0.23317384719849
*/
FatalError
22-Dec-2005 07:39
I recommend using a "while" instead of a "foreach," like this:

<?php
while (list($key, $val) = each($array)) {
   // Do something...
}
?>

This gives you more control and gets rid of some problems that you may have with the foreach statement.
janezr at jcn dot si
10-Nov-2005 05:06
If you want to "look-ahead" values in an associative or non-continuous array, this might help:

<?
$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]] ;
  ...
}
?>
boxer at racaboxer dot com dot br
10-Nov-2005 02:19
To do tables with cells alleatories...

<?
foreach($result as $item)
{
$x++;
if(($x % 2)==0) {
?>
 <tr>
  <td align='center' valign='middle' bgcolor='#FFFFFF' width='300'>
<img src="<?=$item['src'];?>" border="<?=$item['border'];?>" alt="<?=$item['alt'];?>">
  </td>
  <td align='center' valign='middle' bgcolor='#FFFFFF' width='300'>
<?=$item['obs'];?>
  </td>
 </tr>
<? } else { ?>
 <tr>
  <td align='center' valign='middle' bgcolor='#FFFFFF' width='300'>
<?=$item['obs'];?>
  </td>
  <td align='center' valign='middle' bgcolor='#FFFFFF' width='300'>
<img src="<?=$item['src'];?>" border="<?=$item['border'];?>" alt="<?=$item['alt'];?>">
  </td>
 </tr>
<?
}
}
?> 

Just it !
Flavio Tubino From Blumenau, Brazil
08-Oct-2005 02:59
Like the FOR statement, you can also write:

<?php
$a_array=array("a","b","c");
foreach($a_array as $key=>$value):
   print $key." = ".$value."<br>";
endforeach;
?>
Flavio From Brazil
08-Oct-2005 02:55
Like the FOR statement, you can also write:

<?php
foreach($i=1;$i<10;$i++):
   print $i;
endforeach;
?>
retula AT gmail DOT com
05-Oct-2005 09:54
Here is a cool script to optimize all the tables in a database! (mysql only)

<?php

// connect to the db
mysql_connect("host","username","pw");
mysql_select_db("database");

//get all tables
$alletabellen = mysql_query("SHOW TABLES");

//go trough them, save as an array
while($tabel = mysql_fetch_assoc($alletabellen)){

   //go through the array ( $db => $tabelnaam )
   foreach ($tabel as $db => $tabelnaam) {
  
       //optimize every table
       mysql_query("OPTIMIZE TABLE `".$tabelnaam."`") or die(mysql_error());
   }
}

?>

Enjoy!
Oto "Zver" Brglez ml.
24-Sep-2005 09:14
You can use you'r own function for creating xml/html tags.

Function :
function tag($tag,$string,$atrib = false){
   if(!is_array($atrib)){
       return "<".$tag.">".$string."</".$tag.">";
   } else {
       $o = "<".$tag;
       foreach($atrib as $key => $val){
           $o .= " ".$key."=\"".$val."\"";
       };
       $o .= ">".$string."</".$tag.">";
       return $o;
   };
}

Usage:
$array[href] = "http://www.php.net";
$array[id] = "testcss";
$array[class] = "simplecssclass";

print(tag("a","PHP Home Page,$array));

Output:
<a href="http://www.php.net" id="testcss" class="simplecssclass">PHP Home Page</a>

You can use this function without attributes. Like this:
print(tag("b",Bold text));

Output:
<b>Bold text</b>
dyer85 at gmail dot com
28-Jul-2005 06:44
Concerning mike's post below, the list and each function style would also work:

<?php
  
   /* Tweak of Mike's original code */
  
   /*
       Additions include Friendly HTML format or normal
       spaces for command line
   */

   /*
       May you never be forced to deal with a structure
       like this in real life...
   */
   $items = array(
       -1,
       0,
       array(
             array(1,2,3,4),
             array(5,6,7,8),
             array(9,10,11,12)
       ),
       array(
             array("a", "b", "c"),
             array("d", "e", "f"),
             array("g", "h", "i")
       )
   );
  
   // HTML formatting
   echo "<pre>\n"; print_array($items, 0); echo "</pre>\n";
 
   function print_array($arr, $level)
   {
       $indent='';

       // Change to false if you want CLI formatting (no &nbsp; entities)
       $html=true;
      
       // Hehe, I've always used 3-spaced tabs
       $indent = $html ? str_repeat('&nbsp;', $level * 3) : $indent = str_repeat(' ', $level *3);
      
       // Changed from foreach
       while ( list(, $item) = each($arr) )
       {     
           if (is_array($item))
           {
               echo $html ? $indent . "Item is an array...<br>\n" :
               $indent . "Item is an array...\n";

               print_array($item, $level+1);
           }
           else
           {
               echo $html ? $indent . "Value at current index: " . $item . "<br>\n" :
               $indent . "Value at current index: " . $item . "\n";
           }
       }
   }
 
?>
mikeb at tracersinfo dot com
27-Jul-2005 01:18
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".
chris at randomcat dot co dot uk
19-Jul-2005 04:19
Just as a note - it's generally not enough to just foreach through $_POST or $_GET, then addslashes() (although this often works)... you could be exposing yourself to a bit of nastiness due to magic quotes.

See the discussion example 3 of mysql_real_escape_string, for a bit more info: http://uk.php.net/manual/en/function.mysql-real-escape-string.php
magistrata at gmail dot com
14-Jul-2005 12:59
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 04:06
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
25-Jun-2005 06:00
The poster who submitted this loop style for iterating over variables by reference:

<?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.
}
?>

Using foreach() means you end up making a copy of the value, and then quickly reassign it to be a reference. This is a waste of the original copy operation.

You may want to consider this, more meaningful and readable alternative:

<?php

reset($object_list);

while (list($key) = each($object_list)) {

   $the_object = & $object_list[$key]; // 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.

}
?>
JaGx
18-Jun-2005 11:55
On the note of Paul's for loop:
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]);
     }
   }
}

------------
The middle part of the for loop is evaluated every time it loops which means the count function is called as many times as it loops. It's always better (performance/speed wise) to put the count as the initialization code:

function foo($x) {
   global $arr; // some Array
   for($i=count($arr)-1;; $i>=0; $i++) {
     if($arr[$i][0] == $x) {
         echo $arr[$i][1]."\n";
         foo($arr[$i][0]);
     }
   }
}
mike at invertedmind dot com
18-Jun-2005 02:24
One great use of foreach is for recursive function calls.  It can handle things that would otherwise need to be hand-coded down to the desired level, which can make for hard-to-follow nesting.

<?
   /*
       May you never be forced to deal with a structure
       like this in real life...
   */
   $items = array(
       -1,
       0,
       array(
           array(1,2,3,4),
           array(5,6,7,8),
           array(9,10,11,12)
       ),
       array(
           array("a", "b", "c"),
           array("d", "e", "f"),
           array("g", "h", "i")
       )
   );
  
   print_array($items, 0);
  
   function print_array($arr, $level)
   {
       $indent = str_repeat("&nbsp;", $level * 4);
      
       foreach ($arr as $item)
       {
           if (is_array($item))
           {
               print $indent . "Item is an array...<br>\n";
               print_array($item, $level + 1);
           }
           else
               print $indent . "Value at current index: " . $item . "<br>\n";
       }
   }
  
?>

This will output:

Value at current index: -1
Value at current index: 0
Item is an array...
   Item is an array...
       Value at current index: 1
       Value at current index: 2
       Value at current index: 3
       Value at current index: 4
   Item is an array...
       Value at current index: 5
       Value at current index: 6
       Value at current index: 7
       Value at current index: 8
   Item is an array...
       Value at current index: 9
       Value at current index: 10
       Value at current index: 11
       Value at current index: 12
Item is an array...
   Item is an array...
       Value at current index: a
       Value at current index: b
       Value at current index: c
   Item is an array...
       Value at current index: d
       Value at current index: e
       Value at current index: f
   Item is an array...
       Value at current index: g
       Value at current index: h
       Value at current index: i

And it could recurse as far as you want it to go.
30-May-2005 01:17
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.
dave at davedelong dot com
29-May-2005 06:42
A "cheap" way to sort a directory list is like so  (outputs HTML, one indent is 3 non-breaking spaces):

<?php
function echo_Dir($dir, $level) {
   //create an empty array to store the directories:
   $dirs = array();
   //if we were given a directory to list...
   if (is_dir($dir)) {
       //and if we can open it...
       if ($handle = opendir($dir)) {
           //change directory:
           chdir($dir);
           //iterate through the directory
           while (false !== ($file = readdir($handle))) {
               if ($file != "." && $file != "..") {
                   if (is_dir($file)) {
                       //only add legit directories to the array
                       array_push($dirs,$file);
                   }//end if
               }//end if
           }//end while
           //sort the array
           sort($dirs);
           //NOW handle each directory via a foreach loop
           foreach ($dirs as $i => $file) {
               $to_echo = str_repeat("\t",$level+1) . str_repeat("&nbsp;",$level*3) . $file . "<br>";
               echo $to_echo;
               echo_Dir($file,$level+1);   
           }//end foreach
           //return to the parent directory
           chdir("../");
       }//end if
       //close the handle
       closedir($handle);
   }//end if
}//end function
?>

For an example of what this outputs, check out http://www.davedelong.com/php/echodir.php
mark at myipower dot com
26-May-2005 10:10
Here is a solution to an earlier comment I found that worked well for me. It only goes 4 deep on a complex array or object but could go on forever I would imagine.

foreach($_SESSION as $value => $lable1){
   echo "The elements of Value1 <B>" . $value . "</B> is <B>" . $lable1 . "</B><br/>\n";
   if(is_array($lable1) || is_object($lable1)) {
       foreach($lable1 as $value2 => $lable2){
           echo "The elements of Value2 <B>" . $value2 . "</B> is <B>" . $lable2 . "</B><br/>\n";
           if(is_array($lable2) || is_object($lable2)) {
               foreach($lable2 as $value3 => $lable3){
                   echo "The elements of Value3 <B>" . $value3 . "</B>is <B>" . $lable3 . "</B><br/>\n";
                   if(is_array($lable3) || is_object($lable3)) {
                       foreach($lable3 as $value4 => $lable4){
                           echo "The elements of Value4 <B>" . $value4 . "</Bis <B>" . $lable4 . "</B>><br/>\n";
                       }
                   }
               }
           }
       }
       echo "<br>";
   }
}
flobee at gmail dot com
22-May-2005 04:32
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.
flobee at gmail dot com
22-May-2005 04:31
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.
wrm at metrushadows dot com
22-May-2005 01:10
Another example for printing out arrays.

<?php

$array = array(
1 => 'milk',
2 => 'eggs',
3 => 'bread'
);

foreach ($array as $array => $value) {
           echo "$value<br />";
}

?>
fred at flintstone dot com
21-May-2005 12:40
<?
You can easily use FOREACH to show all POST and GET variables from a form submission

function showpost_and_get()
 {
  print "<hr><h2>POST</h2><br>";
  foreach($_POST as $varName => $value)
  {
   $dv=$value;
     $dv=$value;
     print "Variable: $varName Value: $dv<br>";
   };

  print "<hr><h2>GET</h2><br>";
  foreach($_GET as $varName => $value)
  {
   $dv=$value;
     print "Variable: $varName Value: $dv<br>";
   };

 }
Paul Chateau
17-May-2005 02:01
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:

$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
badbrush at pixtur dot de
16-May-2005 01:22
another WARNING about report #26396 having status "wont fix":

Beware of using foreach in recursive functions like...

function sort_folders(&$items, $parent,$level) {
   foreach($items as $item) {
     if($item->parent == $parent) {

         print $item;
         // call recursively...
         sort_folders(&$items, $item, $level+1);
       }
   }
}
        
I struggled a few hours with this code, because I thought the passing the array by reference would be the problem. Infact you can only have ONE foreach for an array at any given time. A foreach inside another foreach does not work.

The manual should definately give some hints about this behaviour.

 pixtur
Michael T. McGrew
13-May-2005 01:11
This can be used to creat a list of urls for a nav bar or links section etc. If you draw the values of array from a mysql database it can be very usefull.

<?php
$arr = array(news, events);
foreach ($arr as $value) {
   echo "<tr><td>Manage <a href=\"./".$value.".php\">".$value."</a></td></tr>";
}
?>
will return
<tr>
<td>Manage <a href="./news.php">news</a>
</td>
</tr>
<tr><td>Manage <a href="./events.php">events</a>
</td>
</tr>
Elvin
24-Apr-2005 04:10
I wrote this code to add each post from a user to every users' txt file. But it only adds the message to the last user in users.txt. The reason of that is...(questmark)

<?php
session_start();
header("Cach-control:private");

$name=$_SESSION['name'];

$nameframe=$name.".txt";
$message=$_POST['message'];

$wierdchars = array("\'", "\"", "\\", ":-)", ":-D", ":-p", ":-(", "=p", ">:0", ":-[", ":-/", ":-\\", ":-X", ":-?", "B-)");

$newchars = array (stripslashes("\'"), stripslashes("\""), "\\", "<img src='smile.gif'>", "<img src='opensmile.gif'>", "<img src='tounge.gif'>", "<img src='sad.gif'>", "<img src='tounge.gif'>", "<img src='yelling.gif'>", "<img src='embarrased.gif'>", "<img src='sosoleft.gif'>", "<img src='sosoright.gif'>", "<img src='quiet.gif'>", "<img src='confused.gif'>", "<img src='cool.gif'>");

$newmessage=str_replace($wierdchars, $newchars, $message);

$fontcolor=$_POST['fontcolor'];

$fontsize=$_POST['fontsize'];

$fontface=$_POST['fontface'];

$users=file("users.txt");

foreach($users as $user)
 {
$nameframed=$user.".txt";
$thefile=file_get_contents($nameframed);
$file=fopen($nameframed, "w+");
$body=$name."|".$newmessage."\n";
$body2=$body.$thefile;
$write=fwrite($file,$body2);
fclose($file);
 }
echo "<html><head><title>Adding info...</title>";
echo "<script>window.location='frame.php';</script>";
echo "</head>";
echo "<!--Removes ads form page</head><body>";
?>
ldv1970
27-Mar-2005 09:53
To the 18-Mar-2005 03:05 post:

See URL: http://bugs.php.net/bug.php?id=30914

The behaviour you describe is incorrect, but the problem might not be with PHP itself.
19-Mar-2005 04:05
It seems that foreach returns different variable types depending on which syntax you use and which version of PHP you are running.

If you use this syntax:

       foreach($array as  $key => $val) {

then the $val variable is a string (or whatever the actual value in the array is).

But if you use this syntax:

       foreach($array as  $val) {

then it appears that the $val variable is an array in PHP 4.3.10, and it is a string (or whatever) in versions 4.3.1, 4.3.2, and 4.3.6 (I haven't tested any other version).
xardas@spymac com
19-Feb-2005 11:35
Quote:
-------------------------
It makes sense, since you cannot call only keys from an array with foreach().
-------------------------
Why not?
<?php
foreach(array_keys($array) as $string)
{
print 'array key is '.$string;
}
?>
14-Dec-2004 11:29
This is a summary of bug report #26396 having status "wont fix", so the following is not a bug (report), but may need extra highlighting so the novice programmer (like me) can make sense of the second note given above.

Note:  Also note that foreach operates on a copy of the specified array and 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. However, the internal pointer of the original array is advanced with the processing of the array. Assuming the foreach loop runs to completion, the array's internal pointer will be at the end of the array.

<?
$myArray = array("a", "b");

foreach($myArray as $anElement) {
  foreach($myArray as $anotherElement) {
   echo $anotherElement;
  }
}
?>

results in "abab", as each foreach works on a copy of $myArray.

However:

<?
$myArray = array("a", "b");

function b() {
  global $myArray;
 
  foreach($myArray as $anotherElement) {
   echo $anotherElement;
  }
}

function a() {
  global $myArray;
 
  foreach($myArray as $anElement) {
   b();
  }
}

a();
?>

results in "ab", ie. both foreach work on the same instance of $myArray because it is referenced as a global variable. Nevertheless, to the casual observer both variants seem equivalent and therefore should produce the same output.
gardan at gmx dot de
08-Oct-2004 03:21
(PHP 5.0.2)
Pay attention if using the same variable for $value in both referenced and unreferenced loops.

$arr = array(1 => array(1, 2), 2 => array(1, 2), 3 => array(1, 2));
foreach($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($value) before entering the next foreach().
Scarab <scarab_at_scarab_dot_name>
29-Jun-2004 09:43
It is possible to suppress error messages from foreach, using type casting:
<?
foreach((array)$myarr as $myvar) {
...
}
?>
turadg at berkeley dot edu
22-May-2004 08:19
The documentation above says "the internal pointer of the original array is advanced with the processing of the array".

In my experience, it's more complicated than that.  Maybe it's a bug in 4.3.2 that I'm using.

If the array variable is created by =& assignment, then it works as described.  You can use current() within the loop to see the next element.

If the array variable is created by an = assignment, the foreach() doesn't advance the pointer.  Instead you must use next() within the loop to peek ahead.

The code below demonstrates.  On my system, the output is the same for both blocks, though one uses next() and the other current().

<?php
$originalArray = array("first", "second", "third", "fourth", "fifth");

print "the array:\n";
print_r($originalArray);

print "\noriginalArray with next():\n";
foreach ($originalArray as $step) {
   $afterThis = next($originalArray);
   print "$step,$afterThis\n";
}

$aliasArray =& $originalArray;

print "\naliasArray with current():\n";
foreach ($aliasArray as $step) {
   $afterThis = current($aliasArray);
   print "$step,$afterThis\n";
}
?>
scott at slerman dot net
18-Apr-2004 11:27
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 02:50
There is a really really big pitfall to watch out for if you are using "foreach" and references.

Recall this example:
<?
$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:
<?
// 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:

<?
$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
07-Feb-2004 02:05
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;

}

?>
thomas dot kaarud at netcom dot no
03-Feb-2004 09:41
A more elegant way to do this, without involving new arrays or making PHP5-specific code, would be:

<?php
foreach ($a as $x => $a) {
   echo "$b[$x] : $a"; }
?>
Joseph Kuan
15-Jan-2004 01:42
<?php
Or use array_combine.

$c = array_combine($a, $b)
foreach($c as $aKey => $bVal) {
   echo $aKey;
   echo $bVal;
}
?>
endofyourself at yahoo dot com
02-Jan-2004 07:36
If you are trying to do something like:

<?PHP

foreach(
     $someArray1 as $someValue1 ,
     $someArray2 as $someValue2
) {

 echo $someValue1;
 echo $someValue2;

}

?>

Pleas note that this IS NOT possible (although it would be cool). However, here is another way to acheive a similar effect:

<?PHP

for(
     ;
     list(, $someValue1 ) = each( $someArray1 ) ,
     list(, $someValue2 ) = each( $someArray2 )
     ;
) {

 echo $someValue1;
 echo $someValue2;

}

?>
php at electricsurfer dot com
23-Apr-2003 04:33
[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
02-Jan-2003 07:29
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 :)
18-Sep-2002 12:06
"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):
foreach ($array as $array) {
   // ...
}

While this won't:
while (list(, $array) = each($array)) {
   // ...
}
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