给出Php错误in_array（）null

I followed a tutorial on making a web crawler app. I just simply pulls all the links from a page and then follows them. I have a problem with pushing the foreach loop of links to the global variable. I keep getting an error that says the second variable in the in_array should be an array which is what i set it to. Is there anything there you guys might see bugging up the code?

Error:

in_array() expects parameter 2 to be array, null given

HTML:

       <?php

    $to_crawl = "http://thechive.com/";

$c = array();

    function get_links($url){
        global $c;
        $input = file_get_contents($url);
        $regexp = "<a\s[^>]*href=(\"??)([^\" >]*?)\\1[^>]*>(.*)<\/a>";

        preg_match_all("/$regexp/siU", $input, $matches);

        $l = $matches[2];

        $base_url = parse_url($url, PHP_URL_HOST);

        foreach($l as $link){
            if(strpos($link, '#')){
                $link = substr($link, 0, strpos($link, '#'));
            }

            if(substr($link, 0, 1) == "."){
                      $link = substr($link, 1);
            }

            if(substr($link, 0, 7) == "http://"){
                              $link = $link;
                    } elseif(substr($link, 0, 8) == "https://"){
                              $link = $link;
                    } elseif(substr($link, 0, 2) == "//"){
                              $link = substr($link, 2);
                    } elseif(substr($link, 0, 1) == "#"){
                              $link = $url;
                    } elseif(substr($link, 0, 7) == "mailto:"){
                              $link = "[".$link."]";
                    } else{
                        if(substr($link, 0,1) != "/"){
                            $link = $base_url."/".$link;
                        } else{
                            $link = $base_url.$link;
                        }
                    }
            if(substr($link, 0, 7) != "http://" && substr($link, 0, 8) != "https://" && substr($link, 0, 1) != "["){
             if(substr($link, 0 , 8) == "https://"){
                    $link = "https://".$link;
             } else{
                $link= "http://".$link;
             }
            }

        if (!in_array($link, $c)){
            array_push($c, $link);
            }


        }
    }

    get_links($to_crawl);

    foreach($c as $page){
        get_links($page);
    }

    foreach($c as $page){
        echo $page."<br/ >";
    }

    ?>

Trying to make "global" your $c at each iteration is a bad design. You should avoid "global" when it's possible.

Here I see 2 choices :

1/ Pass your array as reference (search google for that) in parameter of the "get_links" function. It will allow you to fill the array from your function.

Exemple :

function getlinks($url, &$links){
    //do your stuff to find the links
    //then add each link to the array
    $links[] = $oneLink;
}

$allLinks = array();
getlinks("thefirsturl.com", $allLinks);
//call getlinks as many as you want 
//then your array will contain all the links
print_r($allLinks);

Or 2/ Make "get_links" return an array of links, and concatenate it into a bigger one to store all your links.

function getlinks($url){
    $links = array(); 
    //do your stuff to find the links
    //then add each link to the array
    $links[] = $oneLink;
    return $links;
}

$allLinks = array();
$allLinks += getlinks("thefirsturl.com");
//call getlinks as many as you want. Note the concatenation operator +=
print_r($allLinks);