检查url是在线还是离线——

function get_http_response_code($theURL) {
    $headers = @get_headers($theURL);
    return substr($headers[0], 9, 3);
}

这是一个解决方案，只读取源代码的第一个字节…如果file_get_contents失败，返回false…这也适用于远程文件，如图像。

 function urlExists($url)
{
    if (@file_get_contents($url,false,NULL,0,1))
    {
        return true;
    }
    return false;
}

function URLIsValid($URL)
{
    $exists = true;
    $file_headers = @get_headers($URL);
    $InvalidHeaders = array('404', '403', '500');
    foreach($InvalidHeaders as $HeaderVal)
    {
            if(strstr($file_headers[0], $HeaderVal))
            {
                    $exists = false;
                    break;
            }
    }
    return $exists;
}

function url_exists($url) {
    $headers = @get_headers($url);
    return (strpos($headers[0],'200')===false)? false:true;
}

$url = 'http://google.com';
$not_url = 'stp://google.com';

if (@file_get_contents($url)): echo "Found '$url'!";
else: echo "Can't find '$url'.";
endif;
if (@file_get_contents($not_url)): echo "Found '$not_url!";
else: echo "Can't find '$not_url'.";
endif;

// Found 'http://google.com'!Can't find 'stp://google.com'.

以上所有解决方案+额外的糖。(终极AIO解决方案)

/**
 * Check that given URL is valid and exists.
 * @param string $url URL to check
 * @return bool TRUE when valid | FALSE anyway
 */
function urlExists ( $url ) {
    // Remove all illegal characters from a url
    $url = filter_var($url, FILTER_SANITIZE_URL);

    // Validate URI
    if (filter_var($url, FILTER_VALIDATE_URL) === FALSE
        // check only for http/https schemes.
        || !in_array(strtolower(parse_url($url, PHP_URL_SCHEME)), ['http','https'], true )
    ) {
        return false;
    }

    // Check that URL exists
    $file_headers = @get_headers($url);
    return !(!$file_headers || $file_headers[0] === 'HTTP/1.1 404 Not Found');
}

例子:

var_dump ( urlExists('http://stackoverflow.com/') );
// Output: true;