为什么我收到此错误注意：未定义索引：主机

Question

my sample code is here

include 'simple_html_dom.php';
function get_all_links($url){
    global $host;
    $html = new simple_html_dom();
    $html->load(file_get_contents($url));

    foreach($html->find('a') as $a){
        $host1 = parse_url($a->href);
        $host = parse_url($url);
            if($host1['host'] == $host['host']){
                    $data[] = $a->href;
            }
    }
    return $data;

}
$links = get_all_links("http://www.example.com/");

foreach($links as $link){
   echo $link."<br />";
}

When I try this code, I got this error: Notice: Undefined index: host in... What's wrong in my code? Please suggest me some helping code, Thanks in Advance.

Answer 1

You need to check if the arrays contain entries for 'host' using isset before assuming they exist:

if (isset($host1['host']) && isset($host['host']) 
        && $host1['host'] == $host['host']) {

Or you can use @ to suppress warnings from the check.

if (@$host1['host'] == @$host['host']) {

However, you'll need to double-check that the latter works as you desire when both are missing.

Update: As the others pointed out there is also array_key_exists . It will handle null array values whereas isset returns false for null values.

Answer 2

As others have answered, both isset() and array_key_exists() will work here. isset() is nice, because it can actually take multiple arguments:

if (isset($array[0], $array[1], $array[2]))
{
    // ...
}

// same as

if (isset($array[0]) && isset($array[1]) && isset($array[2]))
{
    // ...
}

Returning true only if all arguments are set.

Answer 3

you can find out if an array has an index called "host" using array_key_exists

if (array_key_exists($host, "host") && array_key_exists($host1, "host") && ...)

http://us3.php.net/manual/en/function.array-key-exists.php