如何写一个会产生我想要的结果的foreach

Question

我很难从数组中获取正确的数据。我写了一个嵌套的foreach循环，但内部循环抛出了“为foreach（）提供的”无效参数“错误。有人能帮我解决这个问题吗？谢谢。

foreach($row as $val) 
{ 
    echo $val['title'].'<br>'; 
    echo $val['author'].'<br>'; 
    echo $val['post'].'<br>'; 
    echo $val['entry_date'].'<br>'; 
    echo $val['comments'].'<br>'; 

    foreach($val as $val2) 
    { 
     echo $val['comments'].'<br>'; 
    } 
} 

---

Array 
(
    [title] => First Blog 
    [author] => Administrator 
    [post] => Testing entry number one 
    [entry_date] => Fri, 23 Oct 2009 
    [comments] => Array 
     (
      [0] => Array 
       (
        [commenter] => Sally Anderson 
        [comments] => comment 1 post 1 
        [comment_date] => October 24th, 2009 at 5:24 AM 
       ) 

      [1] => Array 
       (
        [commenter] => Mike Jones 
        [comments] => comment 2 post 1 
        [comment_date] => October 24th, 2009 at 5:21 AM 
       ) 
     ) 
) 
Array 
(
    [title] => Second Blog 
    [author] => Administrator 
    [post] => Testing entry number two 
    [entry_date] => Sat, 24 Oct 2009 
    [comments] => Array 
     (
      [0] => Array 
       (
        [commenter] => Sally Anderson 
        [comments] => comment 1 post 2 
        [comment_date] => October 24th, 2009 at 5:21 AM 
       ) 

      [1] => Array 
       (
        [commenter] => Mike Jones 
        [comments] => comment 2 post 2 
        [comment_date] => October 24th, 2009 at 5:21 AM 
       ) 
     ) 
) 

Answer 1

假设$rows是你的问题（数组的数组）的底部结构，那么：

foreach ($rows as $row) { 
    echo <<<END 
$row[title]<br> 
$row[author]<br> 
$row[post]<br> 
$row[entry_date]<br> 
END; 
    foreach ($row['comments'] as $comment) { 
    echo <<<END 
$comment[comments]<br> 
$comment[commentor]<br> 
$comment[comment_date]<br> 
END; 
    } 
} 

我强烈建议你选择有意义的名称（如$comment和$row）而不是无意义的名字，如$val和$val2，因为这些只会导致混淆。

另外我在修改后的版本中使用了heredoc syntax，因为我倾向于认为可以使事情更具可读性，但这是可选的。一个更好的选择可能是：

<?php foreach ($rows as $row): ?> 
<?php echo $row['title'] ?><br> 
<?php echo $row['post'] ?><br> 
<?php echo $row['entry_date'] ?><br> 
<?php foreach ($row['comments'] as $comment): ?> 
<?php echo $comment['comments'] ?><br> 
<?php echo $comment['commentor'] ?><br> 
<?php echo $comment['comment_date'] ?><br> 
<?php endforeach; ?> 
<?php endforeach; ?> 

如果你有很多HTML散布的话，这会很有用。上述切换到使用alternative control structures，这是可选的，但通常被认为在这种类型的代码更易读。

最后，你可以PHP short tags，有些人不喜欢（或者是因为他们可能被禁用或者用XML处理指令接口），但我一般喜欢：

<? foreach ($rows as $row): ?> 
<?= $row['title'] ?><br> 
<?= $row['post'] ?><br> 
<?= $row['entry_date'] ?><br> 
<? foreach ($row['comments'] as $comment): ?> 
<?= $comment['comments'] ?><br> 
<?= $comment['commentor'] ?><br> 
<?= $comment['comment_date'] ?><br> 
<? endforeach; ?> 
<? endforeach; ?> 

Answer 2

变化

foreach($val as $val2) 
{ 
    echo $val['comments'].'<br>'; 
} 

至

foreach($val['comments'] as $val2) 
{ 
    echo $val2['comments'].'<br>'; 
}