php 取得文件扩展名的三种方法(改进版)

//取文件的扩展名
//by http://bbs.it-home.org
//method 1
function get_file_ext_1($fileName){
    $retval="";
    $pt=strtpos($fileName,".");
    if($pt){
        $retval=substr($fileName,$pt+1,strlen($fileName)-$pt);
    }
    if($retval!==""){
        return $retval;
    }
    return false;
}
//method two
function get_file_ext_2($fileName){
        $extend = pathinfo($fileName);
        $extend = strtolower($extend['extension']);
        if(is_string($extend)){
            return $extend;
        }
        return false;
    }
//method three
function get_file_ext_3($fileName){
    $extend =explode(".",$fileName);
    $va=count($extend)-1;
    $extend =$extend[$va];
    if(is_string($extend)){
        return $extend;
    }
    return false;
}
?>