PHP: Hypertext Preprocessor

continue

(PHP 4, PHP 5, PHP 7, PHP 8)

continue è impiegato all'interno delle strutture di iterazione per saltare il resto del ciclo corrente e riprendere l'esecuzione dalla verifica della condizione di controllo e quindi dall'inizio dell'iterazione successiva.

Nota: In PHP la struttura switch è considerata una struttura di iterazione ai fini del comando continue. continue si comporta come break (quando nessun argomento viene passato) ma solleverà un avvertimento poiché è probabile che si tratti di un errore. Se uno switch è dentro un loop, continue 2 continuerà con la prossima iterazione del loop esterno.

continue accetta un argomento numerico facoltativo che indica il numero di livelli di strutture iterative annidate per i quali si intende concludere il ciclo attuale. Il valore predefinito è 1, perciò salta alla fine del ciclo corrente.

<?php
foreach ($arr as $key => $value) {
    if (!($key % 2)) { // salta i numeri pari
        continue;
    }
    do_something_odd($value);
}

$i = 0;
while ($i++ < 5) {
    echo "Esterno<br />\n";
    while (1) {
        echo "Medio<br />\n";
        while (1) {
            echo "Interno<br />\n";
            continue 3;
        }
        echo "Questa frase non viene mai mostrata.<br />\n";
    }
    echo "Neanche questa.<br />\n";
}
?>

Omettere il punto e virgola dopo continue può creare confusione. Segue un esempio di cosa non andrebbe fatto.

<?php
for ($i = 0; $i < 5; ++$i) {
    if ($i == 2)
        continue
    print "$i\n";
}
?>

Ci si potrebbe aspettare come risultato il seguente :

**Changelog per `continue`**
Versione	Descrizione
7.3.0	`continue` all'interno di uno `switch` che sta tentando di agire come un'istruzione `break` per lo `switch` innescherà un `E_WARNING`.

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User Contributed Notes 7 notes

down

138

jaimthorn at yahoo dot com ¶

14 years ago

The remark "in PHP the switch statement is considered a looping structure for the purposes of continue" near the top of this page threw me off, so I experimented a little using the following code to figure out what the exact semantics of continue inside a switch is:

<?php

    for( $i = 0; $i < 3; ++ $i )
    {
        echo ' [', $i, '] ';
        switch( $i )
        {
            case 0: echo 'zero'; break;
            case 1: echo 'one' ; XXXX;
            case 2: echo 'two' ; break;
        }
        echo ' <' , $i, '> ';
    }

?>

For XXXX I filled in

- continue 1
- continue 2
- break 1
- break 2

and observed the different results.  This made me come up with the following one-liner that describes the difference between break and continue:

continue resumes execution just before the closing curly bracket ( } ), and break resumes execution just after the closing curly bracket.

Corollary: since a switch is not (really) a looping structure, resuming execution just before a switch's closing curly bracket has the same effect as using a break statement.  In the case of (for, while, do-while) loops, resuming execution just prior their closing curly brackets means that a new iteration is started --which is of course very unlike the behavior of a break statement.

In the one-liner above I ignored the existence of parameters to break/continue, but the one-liner is also valid when parameters are supplied.

down

Nikolay Ermolenko ¶

15 years ago

Using continue and break:



<?php

$stack = array('first', 'second', 'third', 'fourth', 'fifth');



foreach($stack AS $v){

    if($v == 'second')continue;

    if($v == 'fourth')break;

    echo $v.'<br>';

}

/*



first

third



*/



$stack2 = array('one'=>'first', 'two'=>'second', 'three'=>'third', 'four'=>'fourth', 'five'=>'fifth');

foreach($stack2 AS $k=>$v){

    if($v == 'second')continue;

    if($k == 'three')continue;

    if($v == 'fifth')break;

    echo $k.' ::: '.$v.'<br>';

}

/*



one ::: first

four ::: fourth



*/



?>

down

Koen ¶

12 years ago

If you use a incrementing value in your loop, be sure to increment it before calling continue; or you might get an infinite loop.

down

rjsteinert.com ¶

13 years ago

The most basic example that print "13", skipping over 2.

<?php
$arr = array(1, 2, 3);
foreach($arr as $number) {
  if($number == 2) {
    continue;
  }
  print $number;
}
?>

down

www.derosetechnologies.com ¶

20 years ago

In the same way that one can append a number to the end of a break statement to indicate the "loop" level upon which one wishes to 'break' , one can append a number to the end of a 'continue' statement to acheive the same goal. Here's a quick example:

<?
    for ($i = 0;$i<3;$i++) {
        echo "Start Of I loop\n";
        for ($j=0;;$j++) {
            
            if ($j >= 2) continue 2; // This "continue" applies to the "$i" loop 
            echo "I : $i J : $j"."\n";
        }
        echo "End\n";
    }
?>

The output here is:
Start Of I loop
I : 0 J : 0
I : 0 J : 1
Start Of I loop
I : 1 J : 0
I : 1 J : 1
Start Of I loop
I : 2 J : 0
I : 2 J : 1

For more information, see the php manual's entry for the 'break' statement.

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tufan dot oezduman at gmail dot com ¶

18 years ago

a possible explanation for the behavior of continue in included scripts mentioned by greg and dedlfix above may be the following line of the "return" documentation: "If the current script file was include()ed or require()ed, then control is passed back to the calling file." 
The example of greg produces an error since page2.php does not contain any loop-operations. 

So the only way to give the control back to the loop-operation  in page1.php would be a return.

down

Geekman ¶

16 years ago

For clarification, here are some examples of continue used in a while/do-while loop, showing that it has no effect on the conditional evaluation element.

<?php
// Outputs "1 ".
$i = 0;
while ($i == 0) {
    $i++;
    echo "$i ";
    if ($i == 1) continue;
}

// Outputs "1 2 ".
$i = 0;
do {
    $i++;
    echo "$i ";
    if ($i == 2) continue;
} while ($i == 1);
?>

Both code snippets would behave exactly the same without continue.

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