php自定义函数返回中文乱码

纯野生程序爱好者写的php代码，主程序里case'subscribe'中文提示可以用echo正常输出'您好'，但echo函数onclick里返回的中文就是乱码，请明白的朋友给指点一下，谢谢。

switch ($mEvent) {

case 'subscribe':
$contentStr = "您好！";
break;
case 'CLICK':
$contentStr = onclick($fromUsername, $mEventkey);
break;

default:

echo 'success1';
exit();

}

function onclick($fUserid, $fKeyvalue){
    $fResult = NULL;
    switch($fKeyvalue){
            case 'V1001_INQUIRE':
                    break;
            case 'V1001_SIGNUP':
                    session_id($fUserid);
                    session_start();
                    if (isset($_SESSION['s_check'])) {
                        if ($_SESSION['s_check']==0) {
                            $fResult = "1请输入注册码：";                            
                        }else if ($_SESSION['s_check']==1) {
                            $fResult = "2您是已注册用户。";
                        }else if ($_SESSION['s_check']==2) {
                            $_SESSION['s_check'] = 0;
                            $fResult = "3请输入注册码：";
                        }else {
                            echo 'success';
                            exit;
                        }
                    }else {
                        if (checksignup($fUserid)) {
                            $_SESSION['s_check'] = 1;
                            $fResult = "4您是已注册用户。";
                        }else {
                            $_SESSION['s_check'] = 0;
                            $fResult = "5请输入注册码：";
                        }

                    }

检查一下页面编码，可以声明一下编码试试