How to check if a given value is a valid URL

I need some function to check is the given value is a url.

I have code:

<?ph开发者_开发知识库p
$string = get_from_db();
list($name, $url) = explode(": ", $string);
if (is_url($url)) {
    $link = array('name' => $name, 'link' => $url);
} else {
    $text = $string;
}
// Make some things
?>

If you're running PHP 5 (and you should be!), just use filter_var():

function is_url($url)
{
    return filter_var($url, FILTER_VALIDATE_URL) !== false;
}

Addendum: as the PHP manual entry for parse_url() (and @Liutas in his comment) points out:

This function is not meant to validate the given URL, it only breaks it up into the above listed parts. Partial URLs are also accepted, parse_url() tries its best to parse them correctly.

For example, parse_url() considers a query string as part of a URL. However, a query string is not entirely a URL. The following line of code:

var_dump(parse_url('foo=bar&baz=what'));

Outputs this:

array(1) {
  ["path"]=>
  string(16) "foo=bar&baz=what"
}

use parse_url and check for false

<?php
$url = 'http://username:password@hostname/path?arg=value#anchor';

print_r(parse_url($url));

echo parse_url($url, PHP_URL_PATH);
?>

The above example will output:

Array
(
   [scheme] => http
   [host] => hostname
   [user] => username
   [pass] => password
   [path] => /path
   [query] => arg=value
   [fragment] => anchor
)
/path

You can check if ParseUrl returns false.