使用PHP多维数组访问信息时遇到问题

Question

I'm trying to parse the most recent 3 news articles in an RSS feed. After that, it should create a "preview" of the description, and then display the title and the preview. I got it to display the first article 3 times...

<?php
$doc = new DOMDocument();
$doc->load('http://info.arkmediainc.com/CMS/UI/Modules/BizBlogger/rss.aspx?tabid=575593&moduleid=1167800&maxcount=25&t=16c4c7582db87da06664437e98a74210');
$arrFeeds = array();
foreach ($doc->getElementsByTagName('item') as $node) {
    $itemRSS = array ( 
        'title' => $node->getElementsByTagName('title')->item(0)->nodeValue,
        'link' => $node->getElementsByTagName('link')->item(0)->nodeValue,
        'description' => $node->getElementsByTagName('description')->item(0)->nodeValue,
        'pubDate' => $node->getElementsByTagName('pubDate')->item(0)->nodeValue
    );
    array_push($arrFeeds, $itemRSS);
}
$itemRSS = array_slice($itemRSS, 0, 3); // This cuts it down to 3 articles.


for ($i = 0; $i < 3; $i++) 
{
    $title = $itemRSS['title'];
    $description = substr($itemRSS['description'],0,100);
    echo("<h2>".$title."</h2>");
    echo("<br />".$description."<br />");
}
?>

I also got it to "work" (show the first 3) by using a foreach loop...

/*
foreach($itemRSS as $ira)
{
    $title = $itemRSS['title'];
    $description = substr($itemRSS['description'],0,100);
    echo("<h2>".$title."</h2>");
    echo("<br />".$description."<br />");
}
*/

It's commented out because it makes less sense to me.

Please help! Thanks!

Answer 1

You have pushed the rss items into the $arrFeeds and now you can access these by the index, eg $arrFeeds[0] would be the first rss item.

for ($i = 0; $i < 3; $i++) 
{
  $title = $arrFeeds[$i]['title'];
  $description = substr($arrFeeds[$i]['description'],0,100);
  echo("<h2>".$title."</h2>");
  echo("<br />".$description."<br />");
}

But the following is better: with foreach :

$theFirstThreeArticles = array_slice($arrFeeds, 0, 3); // This cuts it down to 3 articles.

foreach($theFirstThreeArticles as $ira)
{
  $title = $ira['title'];
  $description = substr($ira['description'],0,100);
  echo("<h2>".$title."</h2>");
  echo("<br />".$description."<br />");
}

Answer 2

When you use foreach, there are there are two (in your case, but there can be 3) possible "parameters" that it accepts. An array to traverse and a variable to store each element. This example:

$numbers = array('one', 'two');
foreach($numbers as $number) {
    echo "\nNew Iteration\n";
    var_dump($numbers);
    var_dump($number);
}

Will output :

New Iteration
array(2) {
  [0] => string(3) "one"
  [1] => string(3) "two"
}
string(3) "one"

New Iteration
array(2) {
  [0] => string(3) "one"
  [1] => string(3) "two"
}
string(3) "two"

The iterator never modifies the array. It just sets $number to be the value of each element in the array until there are no more elements. The same principle applies to a for loop. The code below will produce the same as above .

$numbers = array('one', 'two');
for($i = 0; $i < count($numbers); $i++) {
    echo "\nNew Iteration\n";
    var_dump($numbers);
    var_dump($numbers[$i]);
}

The same applies when you use multidimensional arrays. Whether you choose for or foreach , you have to access each element in the array. So your code will look something like this:

foreach($rssItems as $rssItem)
{
    $title = $rssItem['title'];
    $description = substr($rssItem['description'],0,100);
    echo("<h2>".$title."</h2>");
    echo("<br />".$description."<br />");
}

I chose to use foreach because I find it's much easier to let PHP handle the iteration. Plus, the foreach line reads properly in English. For each item in $rssItems alias it as $rssItem . Notice the difference between the plural and the singular. The foreach runs its block for each item in $rssItems and for each iteration the variable $rssItem will contain the current value in $rssItems that the loop is on.

Want more of a reason to use foreach ? If you need to work with the key too, foreach will give you both the key and value of every element of the hash (array).

$words = array('hola' => 'hello', 'adios' => 'goodbye', 'gracias' => 'thank you');
foreach($words as $spanishWord => $englishTranslation) {
    echo $spanishWord . " in English is " . $englishTranslation . "\n";
}

Foreach also allows you with SPL to write classes that extend or implement an iterator. Classes that contain collections, can function as a class but can be iterated over. For example:

class PhotoAlbum implements IteratorAggregate {
    private $pictures = array();

    public function __construct($pictures) {
        $this->pictures = $pictures;
    }

    public function addPicture($picture) {
        $this->pictures[] = $picture;
    }

    public function share($friend) {
        // etc..
    }

    public function getIterator() {
        return new ArrayIterator($this->pictures);
    }
}

$album = new PhotoAlbum($picturesArrayFromDB);
foreach($album as $picture) {
    echo $picture;
}