while

(PHP 4, PHP 5)

Los bucles while son el tipo más sencillo de bucle en PHP. Se comportan igual que su contrapartida en C. La forma básica de una sentencia while es:

while (expr)
    sentencia

El significado de una sentencia while es simple. Le dice a PHP que ejecute las sentencias anidadas, tanto como la expresión while se evalúe como TRUE. El valor de la expresión es verificado cada vez al inicio del bucle, por lo que incluso si este valor cambia durante la ejecución de las sentencias anidadas, la ejecución no se detendrá hasta el final de la iteración (cada vez que PHP ejecuta las sentencias contenidas en el bucle es una iteración). A veces, si la expresión while se evalúa como FALSE desde el principio, las sentencias anidadas no se ejecutarán ni siquiera una vez.

Al igual que con la sentencia if, se pueden agrupar varias instrucciones dentro del mismo bucle while rodeando un grupo de sentencias con corchetes, o utilizando la sintaxis alternativa:

while (expr):
    sentencias
    ...
endwhile;

Los siguientes ejemplos son idénticos y ambos presentan los números del 1 al 10:

<?php
/* ejemplo 1 */

$i 1;
while (
$i <= 10) {
    echo 
$i++;  /* el valor presentado sería
                   $i antes del incremento
                   (post-incremento) */
}

/* ejemplo 2 */

$i 1;
while (
$i <= 10):
    echo 
$i;
    
$i++;
endwhile;
?>

add a note add a note

User Contributed Notes 16 notes

up
7
scott at mstech dot com
4 years ago
Just a note about using the continue statement to forego the remainder of a loop - be SURE you're not issuing the continue statement from within a SWITCH case - doing so will not continue the while loop, but rather the switch statement itself.

While that may seem obvious to some, it took a little bit of testing for me, so hopefully this helps someone else.
up
7
chayes at antenna dot nl
12 years ago
At the end of the while (list / each) loop the array pointer will be at the end.
This means the second while loop on that array will be skipped!

You can put the array pointer back with the reset($myArray) function.

example:

<?php
$myArray
=array('aa','bb','cc','dd');
while (list (
$key, $val) = each ($myArray) ) echo $val;
reset($myArray);
while (list (
$key, $val) = each ($myArray) ) echo $val;
?>
up
0
corychristison[AT]NSPAMlavacube[dot]com
9 years ago
While can do wonders if you need something to queue writing to a file while something else has access to it.

Here is my simple example:

<?php

 
function write ($data, $file, $write_mode="w") {
   
$lock = $file . ".lock";
    
// run the write fix, to stop any clashes that may occur
   
write_fix($lock);
    
// create a new lock file after write_fix() for this writing session
   
touch( $lock );
    
// write to your file
   
$open = fopen($file, $write_mode);
   
fwrite($open, $data);
   
fclose($open);
    
// kill your current lock
   
unlink($lock);
  }

  function
write_fix ($lock_file) {
    while(
file_exists($lock_file){
     
// do something in here?
      // maybe sleep for a few microseconds
      // to maintain stability, if this is going to
      // take a while ?? [just a suggestion]
   
}
  }

?>

This method is not recommended for use with programs that will be needing a good few seconds to write to a file, as the while function will eat up alot of process cycles.  However, this method does work, and is easy to implement.  It also groups the writing functions into one easy to use function, making life easier. :-)
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-2
qeremy [atta] gmail [dotta] com
1 year ago
Instead of this usage;

<?php
$arr
= array("orange", "banana", "apple", "raspberry");

$i = 0;
while (
$i < count($arr)) {
  
$a = $arr[$i];
   echo
$a ."\n";
  
$i++;
}
// or
$i = 0;
$c = count($arr);
while (
$i < $c) {
  
$a = $arr[$i];
   echo
$a ."\n";
  
$i++;
}
?>

This could be more efficient;

<?php
while ($a = $arr[1 * $i++]) echo $a ."\n";
?>
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-2
ravenswd at gmail dot com
4 years ago
I find it often clearer to set a simple flag ($finished) to false at the start of the loop, and have the program set it to true when it's finished doing whatever it's trying to do. Then the code is more self-documenting: WHILE NOT FINISHED keep going through the loop. FINISHED EQUALS TRUE when you're done. Here's an example. This is the code I use to generate a random filename and ensure that there is not already an existing file with the same name. I've added very verbose comments to it to make it clear how it works:

<?php
$finaldir
= 'download';

$finished = false;                       // we're not finished yet (we just started)
while ( ! $finished ):                   // while not finished
 
$rn = rand();                          // random number
 
$outfile = $finaldir.'/'.$rn.'.gif';   // output file name
 
if ( ! file_exists($outfile) ):        // if file DOES NOT exist...
   
$finished = true;                    // ...we are finished
 
endif;
endwhile;                               
// (if not finished, re-start WHILE loop)
?>
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-3
yohgaki at hotmail dot com
13 years ago
If you want to traverse array, foreach() is faster than while() a little.
[Benched with PHP4.0.4pl1/Apache DSO/Linux]

i.e.
foreach ($array as $k => $v)
is a little faster than
while (list($k,$v) = each($array))

You might want to use foreach for large arrays.
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-4
virtualjosh at yahoo dot com (Hosh)
10 years ago
I made a test traversing an array (simple, but long, numeric array with numeric keys). My test had a cycle per method, and multiplied each array element by 100.. These were my results:

******************************************************
30870 Element Array Traversing

[test_time] [BEGINS/RESETS @ time_start = 1060977996.689]
0.2373 seg later -> while (list ($key, $val) = each ($array)) ENDS

[test_time] [BEGINS/RESETS @ time_start = 1060977996.9414]
0.1916 seg later -> while (list ($key,) = each ($array))  ENDS

[test_time] [BEGINS/RESETS @ time_start = 1060977997.1513]
0.1714 seg later -> foreach ($array AS $key=>$value) ENDS

[test_time] [BEGINS/RESETS @ time_start = 1060977997.3378]
0.0255 seg later -> while ($next = next($array)) ENDS

[test_time] [BEGINS/RESETS @ time_start = 1060977997.3771]
0.1735 seg later -> foreach ($array AS $value) ENDS
**************************************************************

foreach is fatser than a while (list  - each), true.
However, a while(next) was faster than foreach.

These were the winning codes:

$array = $save;
test_time("",1);
foreach ($array AS $key=>$value)
    $array[$key] = $array[$key] * 100;
test_time("foreach (\$array AS \$key=>\$value)");

$array = $save;
test_time("",1);
reset($array);
while ($next = next($array))
{    $key = key($array);
    $array[$key] = $array[$key] * 100;
}       
test_time("while (\$next = next(\$array))");
*********************************************************
The improvement seems huge, but it isnt that dramatic in real practice. Results varied... I have a very long bidimensional array, and saw no more than a 2 sec diference, but on 140+ second scripts.  Notice though that you lose control of the $key  value (unless you have numeric keys, which I tend to avoid), but it is not always necessary. 

I generally stick to foreach. However, this time, I was getting Allowed Memory Size Exceeded errors with Apache. Remember foreach copies the original array, so this now makes two huge 2D arrays in memory and alot of work for Apache. If you are getting this error, check your loops. Dont use the whole array on a foreach. Instead get the keys and acces the cells directlly. Also, try and use unset and Referencing on the huge arrays.

Working on your array and loops is a much better workaround than saving to temporary tables and unsetting (much slower).
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-4
s dot seitz at netz-haut dot de
6 years ago
Due to the fact that php only interprets the necessary elements to get a result, I found it convenient to concatenate different sql queries into one statement:

<?php

$q1
= 'some query on a set of tables';
$q2 = 'similar query on a another set of tables';

if ( (
$r1=mysql_query($q1)) && ($r2=mysql_query($q2)) ) {

     while ((
$row=mysql_fetch_assoc($r1))||($row=mysql_fetch_assoc($r2))) {

        
/* do something with $row coming from $r1 and $r2 */

     
}
   }

?>

[EDIT BY danbrown AT php DOT net: Contains a bugfix supplied by "Ira" on 14-AUG-09 to address an extra '(' in the leading `if` statement.]
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-3
Ilene Jones
9 years ago
For Perl programmers, break is similar to last

while (1) {
   while(cond) {
       if (error) {
           break 2; // in perl this could have been last;
       }
   }
}
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-4
chris mushy
9 years ago
Just a note to stuart - the reason for this behaviour is because using the while(value = each(array)) construct increments the internal counter of the array as its looped through. Therefore if you intend to repeat the loop, you need to reset the counter. eg:

$one = array("10", "20", "30", "40");
$two = array("a", "b", "c", "d");

$i=0;
while($i < count($one)) {
   reset($two);
   while($a = each($two)) {
       echo $a[1]." - ".$one[$i].", ";
   }
   $i++;
  
}

This produces:

a - 10, b - 10, c - 10, d - 10, a - 20, b - 20, c - 20, d - 20, a - 30, b - 30, c - 30, d - 30, a - 40, b - 40, c - 40, d - 40,
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-4
startide at free dot fr
8 years ago
Talking about while, dropdown menus, and ternary operator which was mentionned before, you can combine them to have drop menu built with a value selected according to your wishses.

<select name="whatever">
<?php
while ($data = mysql_fetch_assoc($requeteID))
{
 
$menu .= '<option value="'.$data['id'].'"';
 
$menu .= ($data['id'] == $_GET['id'] ? ' selected>' :'>');
 
$menu .= $data['name'].'</option>';
}
echo
$menu;
?>
</select>

Therefore if you are creating a form to select data from database, and want the form displayed when search is done to show what parameters have been chosen that will do the trick !!

Let's say I make a search between different sports, I choose football in my form, send my query... then displays are show, the menu will have football selected because of the ternary operator that displays "selected>" on the <option> ;) Enjoy ^^
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-5
Merve
11 years ago
This is an easy way for all you calculator creators to make it do factorials. The code is this:

<?php
$c
= ($a-1);
$d = $a;
while (
$c>=1)
{
$a = ($a*$c);
$c--;
}
print (
" $d! = $a");
?>

$a changes, and so does c, so we have to make a new variable, $d, for the end statement.
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-7
stuart
9 years ago
A note to anyone nesting a while loop inside a while loop....

Consider the example below:

$one = array("10", "20", "30", "40");
$two = array("a", "b", "c", "d");

$i=0;
while($i < count($one)) {
   
    while($a = each($two)) {
        echo $a[1]." - ".$one[$i].", ";
    }
    $i++;
   
}

This will return the following:
a - 10, b - 10, c - 10, d - 10

So in effect the main while loop is only doing one iteration... and not 4 as expected....

Now the example below works as expected..
$i=0;
while($i < count($one)) {
   
    foreach($two as $a) {
        echo $a." - ".$one[$i]."\n";
    }
    $i++;
   
}

by returning:
a - 10, b - 10, c - 10, d - 10, a - 20, b - 20, c - 20, d - 20, a - 30, b - 30, c - 30, d - 30, a - 40, b - 40, c - 40, d - 40

So there is clearly a difference on how while statements work in comparison to other looping structures.

I think it would be good to have an explaination of this strange behaviour.
up
-4
Anonymous
9 years ago
virtualjosh at yahoo dot com (Hosh) wrote on: 16-Aug-2003 12:52

The speedtest is interesting. But the seemingly fastest way contains a pitfall for beginners who just use it because it is fast and fast is cool ;)

Walking through an array with next() will cut of the first entry, as this is the way next() works ;)

If you really need to do it this way, make sure your array contains an empty entry at the beginning. Another way would be to use

<?php
while ($this = current($array) ){
   
do_something($this);
   
next($array);
}
?>

There is an impact on speed for sure but I did not test it. I would advise to stick with conventional methods because current(),next() in while loops is too error prone for me.
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-8
sub7ime at yahoo dot com
8 years ago
I was reading the excellent post by wbryson at gmail dot com and I wanted to just add that the ? : syntax is known as the 'ternary operator' for those who want to learn more about it.
up
-9
dominik at deobald dot org
7 years ago
@stuart:

There's nothing strange or unexpected about your loop's behaviour.

> So in effect the main while loop is only doing one iteration... and not 4 as expected....

That's the wrong conclusion. The outer "while" does all four iterations. However the "inner" loop does nothing for the second, third and fourth run.

> I think it would be good to have an explaination of this strange behaviour.

Here it is:

<?PHP
$i
=0;
while(
$i < count($one)) {
  
   while(
$a = each($two)) {
       echo
$a[1]." - ".$one[$i].", ";
   }
  
$i++;
  
}
?>

The "problem" is your use of "each", which reached the last item after the first iteration of the outer loop. After that, when you come back to the second iteration with the outer loop, "each" still is at the end of the array $two.

If you add a reset($two) in front of the inner "while", you'll get the result you expect.
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