substr（）PHP不适用于数组元素

Question

    $nomadspage = "http://www.nomads.ncep.noaa.gov/pub/data/nccf/com/gfs/prod/";    
    $html = file_get_contents($nomadspage);
    $count = preg_match_all('/<a href="([^"]+)">[^<]*<\/a>/i', $html, $files);

    unset($files[1]); //deletes repeat array from preg_match
    $files = $files[0]; //deletes container array from preg_match

    foreach ($files as $key => $value) {
        if (substr($value, 0, 3) !== "gfs") {
            unset($files[$key]);
        }
    }

    var_dump($files);

I have an array with file names from an HTTP directory. I want to filter these files names so that all of the files that don't start with the three letters gfs are deleted from the array. However, for some reason, the substr() function does not work. It does not pull a substring from the file names. Therefore, the if statement does not work. Anybody know why this is happening and how to fix it?

Answer 1

$files[0] contains the strings that match the entire regular expression, so substr($value, 0, 3) is always "<a ". You should set $files to $files[1], not $files[0], it contains all the matches of the ([^"]+) pattern.

Actually, it's best not to use regular expressions to parse HTML. Use a DOM parser library, such as the DOMDocument class.