PHP: Hypertext Preprocessor

continue

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

continue wird innerhalb von Schleifen verwendet, um den Rest des aktuellen Schleifendurchlaufs abzubrechen und mit der Auswertung der nächsten Bedingung fortzufahren, um dann den nächsten Durchlauf zu beginnen.

Hinweis: In PHP wird das switch-Statement im Sinne von continue als Schleifenstruktur betrachtet. continue verhält sich wie break (wenn keine Argumente übergeben werden), erzeugt aber eine Warnung, da es sich vermutlich um einen Fehler handelt. Falls sich ein switch innerhalb einer Schleife befindet, wird continue 2 mit der nächsten Iteration der äußeren Schleife fortsetzen.

continue akzeptiert ein optionales numerisches Argument, das angibt, wie viele Ebenen umschließender Schleifen bis zu ihrem Ende übersprungen werden sollen. Die Voreinstellung ist 1, so dass zum Ende der aktuellen Schleife gesprungen wird.

<?php
$arr = ['zero', 'one', 'two', 'three', 'four', 'five', 'six'];
foreach ($arr as $key => $value) {
    if (0 === ($key % 2)) { // ignoriere Elemente mit geradem Schlüssel
        continue;
    }
    echo $value . "\n";
}
?>

Die obigen Bespiele erzeugen folgende Ausgabe:

one
three
five

<?php
$i = 0;
while ($i++ < 5) {
    echo "Äußere\n";
    while (1) {
        echo "Mittlere\n";
        while (1) {
            echo "Innere\n";
            continue 3;
        }
        echo "Das hier wird nie ausgegeben.\n";
    }
    echo "Das hier ebenfalls nicht.\n";
}
?>

Die obigen Bespiele erzeugen folgende Ausgabe:

Outer
Middle
Inner
Outer
Middle
Inner
Outer
Middle
Inner
Outer
Middle
Inner
Outer
Middle
Inner

Das Weglassen des Semikolons nach continue kann zu unerwarteten Ergebnissen führen. Hier ist ein Beispiel, das zeigt, was Sie nicht tun sollten.

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

Man könnte meinen, die Ausgabe wäre:

**Changelog für `continue`**
Version	Beschreibung
7.3.0	`continue` innerhalb eines `switch`, das versucht wie eine `break`-Anweisung für das `switch` zu wirken, erzeugt ein `E_WARNING`.

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User Contributed Notes 7 notes

down

140

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 ¶

11 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.

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.

down

tufan dot oezduman at gmail dot com ¶

17 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.

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