require之前要先判断文件是否存在哦

function auto($class){
    if（file_exists("./class/".$class.".php")) {
        require("./class/".$class.".php");
    }
}
function aa($class){
    if（file_exists("./class2/".$class.".php")) {
        require("./class2/".$class.".php");
    }
}