PHP: Hypertext Preprocessor

continue

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

continue 在循环结构用用来跳过本次循环中剩余的代码并在条件求值为真时开始执行下一次循环。

注意: 在 PHP 中 switch 语句被认为是可以使用 continue 的一种循环结构。 continue 的行为类似于没有传递参数的 break ，但会引发警告，因为这可能是一个错误。如果 switch 在循环内， continue 2 将会外部循环中的下一个迭代中继续。

continue 接受一个可选的数字参数来决定跳过几重循环到循环结尾。默认值是 1，即跳到当前循环末尾。

<?php
$arr = ['zero', 'one', 'two', 'three', 'four', 'five', 'six'];
foreach ($arr as $key => $value) {
    if (0 === ($key % 2)) { // 跳过偶数键的成员
        continue;
    }
    echo $value . "\n";
}
?>

以上示例会输出：

one
three
five

<?php
$i = 0;
while ($i++ < 5) {
    echo "Outer\n";
    while (1) {
        echo "Middle\n";
        while (1) {
            echo "Inner\n";
            continue 3;
        }
        echo "This never gets output.\n";
    }
    echo "Neither does this.\n";
}
?>

以上示例会输出：

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

省略 continue 后面的分号会导致混淆。以下例子示意了不应该这样做。

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

希望得到的结果是：

**`continue` 的更新记录**
版本	说明
7.3.0	在 `switch` 中 `continue` 语句试图代替 `break` 语句将会触发 `E_WARNING` 。

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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.