PHP: continue - PHP中文网

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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User Contributed Notes 20 notes

down

134

jaimthorn at yahoo dot com ¶

13 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 ¶

14 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 ¶

10 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 ¶

12 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 ¶

19 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

greg AT laundrymat.tv ¶

18 years ago

You using continue in a file included in a loop will produce an error.  For example:

//page1.php
for($x=0;$x<10;$x++)
   {
    include('page2.php');    
}

//page2.php

if($x==5)
    continue;
else 
   print $x;

it should print

"012346789" no five, but it produces an error:

Cannot break/continue 1 level in etc.

down

tufan dot oezduman at gmail dot com ¶

16 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

clau r jimenez ¶

2 years ago

I've been playing around to see what it does in practice. This is what helped me understand what it does and its difference with using break.

<?php
$i = 0;
while ($i++ < 5) {
    while ($i % 2 === 0) {
        echo "$i is even. \n";
        ####
    }
    echo "$i is odd. \n";
}
?>

Where ####:
 - break: outputs both '$i is even' and '$i is odd' for even numbers.
 - continue: infinite loop as soon as it evaluates true for the first even number.
 - break 2: as soon as it runs, it exits from both loops.
 - continue 2: outputs numbers correctly.

What I understand from this is that break will exit current looping structure and will keep running outer loop code. Continue will make loop get back to evaluation, and will iterate over itself until it evaluates to false. Break 2 will exit 2 levels, which in this case will stop the iteration altogether. Continue 2 will evaluate not the current loop (level 1 so to speak), but the outer loop in this case.

down

Geekman ¶

15 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

-3

skippychalmers at gmail dot com ¶

12 years ago

To state the obvious, it should be noted, that the optional param defaults to 1 (effectively).

down

-1

mparsa1372 at gmail dot com ¶

2 years ago

The continue statement breaks one iteration (in the loop), if a specified condition occurs, and continues with the next iteration in the loop.

This example skips the value of 4:

<?php
for ($x = 0; $x < 10; $x++) {
  if ($x == 4) {
    continue;
  }
  echo "The number is: $x <br>";
}
?>

down

-10

Anonymous ¶

12 years ago

<?php

function print_primes_between($x,$y)

{

    for($i=$x;$i<=$y;$i++) 

   {

        for($j= 2; $j < $i; $j++)  if($i%$j==0) continue 2;

        echo $i.",";

   }

}

?>



This function, using continue syntax, is to print prime numbers between given numbers, x and y.

For example, print_primes_between(10,20) will output:



11,13,17,19,23,29,

down

-9

maik penz ¶

11 years ago

Please note that with PHP 5.4 continue 0; will fail with

PHP Fatal error:  'continue' operator accepts only positive numbers

(same is true for break).

down

-11

net_navard at yahoo dot com ¶

17 years ago

Hello firends

It is said in manually:
continue also accepts an optional numeric argument which tells it how many levels of enclosing loops it should .

In order to understand better this,An example for that:
<?php

/*continue also accepts an optional numeric argument which 
    tells it how many levels of enclosing loops it should skip.*/

for($k=0;$k<2;$k++)
{//First loop

    
    for($j=0;$j<2;$j++)
    {//Second loop

      for($i=0;$i<4;$i++)
      {//Third loop
    if($i>2)
    continue 2;// If $i >2 ,Then it skips to the Second loop(level 2),And starts the next step,
    echo "$i\n";
       }

    }

}

?>

Merry's christmas :)
    
With regards,Hossein

down

-9

dedlfix gives me a hint ¶

18 years ago

a possible solution for 
greg AT laundrymat.tv

I've got the same problem as Greg
and now it works very fine by using
return() instead of continue.

It seems, that you have to use return()
if you have a file included and
you want to continue with the next loop

down

-14

Anonymous ¶

15 years ago

The continue keyword can skip division by zero:
<?php
$i = 100;
while ($i > -100)
{
    $i--;
    if ($i == 0)
    {
        continue;
    }
    echo (200 / $i) . "<br />";
}
?>

down

-10

send at mail dot 2aj dot net ¶

5 years ago

As of PHP 7.0, instead of code executing up until encountering a continue (or break) call outside of a loop statement, the code will simply not execute.

If you need to correct such error cases as part of an upgrade, you may need to substitute either an exit or return to maintain the existing behavior of such legacy code.

<?php

class ok {

    function foo() {
        echo "start\n";

        for ($i = 0; $i < 5; $i++) {
            echo "before\n";
            $this->bar($i);
            echo "after\n";
        }

        echo "finish\n";
    }

    function bar($i) {
        echo "inside iteration $i\n";
        
        if ($i == 3) {
            echo "continuing\n";
            continue;
        }

        echo "inside after $i\n";
    }
}

$ex = new ok();

$ex->foo();

?>

sh> php56 continue.php 
start
before
inside iteration 0
inside after 0
after
before
inside iteration 1
inside after 1
after
before
inside iteration 2
inside after 2
after
before
inside iteration 3
continuing
PHP Fatal error:  Cannot break/continue 1 level in continue.php on line 22
PHP Stack trace:
PHP   1. {main}() continue.php:0
PHP   2. ok->foo() continue.php:31
PHP   3. ok->bar() continue.php:10

sh> php70 continue.php 
PHP Fatal error:  'continue' not in the 'loop' or 'switch' context in continue.php on line 22

Fatal error: 'continue' not in the 'loop' or 'switch' context in continue.php on line 22

down

-17

John ¶

9 years ago

<?php

echo"\n";
echo"\n";

    for ( $i = 0; $i < 5; $i++ ) {

        switch ($i)
        {

            case 0:
                echo $i . "b";
                continue;
                echo $i . "a";
            case 1:    
                echo $i . "b";
                continue 2;
                echo $i . "a";
            case 2:    
                echo $i . "b";
                break;
                echo $i . "a";
            case 3:
                echo $i . "b";
                break 2;
                echo $i . "a";
            case 4:
                echo $i;
            
        }

        echo 9;

    }

echo"\n";
echo"\n";

?>

This results in: 0b91b2b93b

It goes to show that in a switch statement break and continue are the same. But in loops break stops the loop completely and continue just stops executing the current iterations code and moves onto the next loop iteration.

down

-20

szrrya at yahoo dot com ¶

17 years ago

Documentation states:

"continue is used within looping structures to skip the rest of the current loop iteration"

Current functionality treats switch structures as looping in regards to continue.  It has the same effect as break.

The following code is an example:

<?php
for ($i1 = 0; $i1 < 2; $i1++) {
  // Loop 1.
  for ($i2 = 0; $i2 < 2; $i2++) {
    // Loop 2.
    switch ($i2 % 2) {
      case 0:
        continue;
        break;
    }
    print '[' . $i2 . ']<br>';
  }
  print $i1 . '<br>';
}
?>

This outputs the following:
[0]
[1]
0
[0]
[1]
1

Switch is documented as a block of if...elseif... statements, so you might expect the following output:
[1]
0
[1]
1

This output requires you to either change the switch to an if or use the numerical argument and treat the switch as one loop.

down

-32

Rene ¶

17 years ago

(only) the reason that is given on the "Continue with missing semikolon" example is wrong.

the script will output "2" because the missing semikolon causes that the "print"-call is executed only if the "if" statement is true. It has nothing to to with "what" the "print"-call would return or not return, but the returning value can cause to skip to the end of higher level Loops if any call is used that will return a bigger number than 1.

<?php
continue print "$i\n";
?>

because of the optional argument, the script will not run into a "unexpected T_PRINT" error. It will not run into an error, too, if the call after continue does return anything but a number.

i suggest to change it from:
because the return value of the print() call is int(1), and it will look like the optional numeric argument mentioned above.

to
because the print() call will look like the optional numeric argument mentioned above.

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