php简单验证用户名、密码、日期

经测试代码如下：

<?PHP
function is_valid_username($username){
// accepted username length between 5 and 20
 if (preg_match('/^\w{5,20}$/',$username))
 return true;
 else
 return false;
}
function is_valid_password($pwd){
// accepted password length between 5 and 20,start with character.
 if (preg_match(/^[a-zA-Z][0-9a-zA-Z_!$@#^&]{5,20}$/,$pwd))
 return true;
 else
 return false;
}
function is_valid_date($date){
//============ date format dd-mm-yyyy
if(preg_match(/^(\d{2})-(\d{2})-(\d{4})$/,$date,$sdate))
 if(checkdate($sdate[2],$sdate[1],$sdate[3]))
 return true;
}
/*** 以上代码来自jb51.cc ***/
?>