1.

function findexts ($filename) {

       $filename = strtolower($filename) ;

       $exts = split("[/\\.]", $filename) ;

       $n = count($exts)-1;

       $exts = $exts[$n];

       return $exts;

} 

2.

$filename = 'abc.hwp';

$ext = pathinfo($filename, PATHINFO_EXTENSION); 

3.

function getFileextension($file) {

       return end(explode(".", $file));

}