str_ireplace（）不会仅替换最后一个匹配项

I am trying to replace the urls of a web page. I am using DOM to get all the links in the page, loop through the links and find and replace one by one using str_ireplace. The str_ireplace replaces only the last link. When I count, it gives proper count of the number of links to be replaced, but does not replace the links.

    $contents=file_get_contents($_GET['page']);
    $dom = new DOMDocument;
    @$dom->loadHTML($contents);    
    $links = $dom->getElementsByTagName('a');
$c=0;
//Iterate over the extracted links and display their URLs
    foreach ($links as $link){
        //echo $link->nodeValue;
        $arr['retUrl']=$link->getAttribute('href');
        $xyz=json_encode($arr);
        $rurl=$base_url.'?ret_url='.urlencode($xyz);
        echo $arr['retUrl'].'<br>'.$rurl.'<br><br><br>';

        $x=str_ireplace($link->getAttribute('href'),$rurl,$contents,$count);
        $c=$c+$count;
        echo '--'.$count.'--';
    }

    echo $x;

This happens because you output $x, and what is $x? It is $contents with last $link processed. I'm sure you need to save all previous replacements in $contents too. Replace

$x=str_ireplace($link->getAttribute('href'),$rurl,$contents,$count);

with

$contents = str_ireplace($link->getAttribute('href'),$rurl,$contents,$count);

Here you overwrite $contents with every replaced link. After loop - output $contents.

Looking over it, change it to this:

   $x .= str_ireplace($link->getAttribute('href'),$rurl,$contents,$count);