php – mySQLi预处理语句无法get_result()

我对mySQLi感到很困惑.虽然我多年来一直在使用过程式 mysql调用,但我想习惯为它提供的db security / mySQL注入保护制作预备语句.我正在尝试编写一个简单的select语句(是的,我知道为此提供性能增强的程序调用).在运行时,我得到了所有的回声,直到我点击$result = $stmt-> get_result();零件.对我来说这一切看起来都相当简单,但是在mySQLi上阅读手册后,我感到很茫然.任何想法为什么会失败？

*注意：这是一个测试环境,虽然没有对字符进行消毒/转义,但我只将有效内容传递给变量$username和$email.而且,我已经看了很多,以找到我的问题的解决方案.

function checkUsernameEmailAvailability($username,$email) {
    //Instantiate mysqli connection
    @$mysqli = new mysqli(C_HOST,C_USER,C_PASS,C_BASE) or die("Failed to connect to MySQL database...");
    if (!$mysqli)
    {
        echo 'Error: Could not connect to database.  Please try again later...';
        exit;
    } else {
        echo 'mysqli created';
    }

    /* Create a prepared statement */   
    if($stmt = $mysqli -> prepare("SELECT username,email FROM tb_users WHERE username=? OR email=?")) {
        echo '<br />MYSQLi: ';

        /* Bind parameters s - string,b - boolean,i - int,etc */
        $stmt -> bind_param("ss",$username,$email);
        echo '<br />paramsBound...';

        /* Execute it */
        $stmt -> execute();     
        echo '<br />Executed';

        $result = $stmt->get_result();
        echo '<br />Result acquired';

        /* now you can fetch the results into an array - NICE */
        $myrow = $result->fetch_assoc();
        echo '<br />Fetched';


        /* Close statement */
        /$stmt -> close();
        echo '<br />Done mysqli';
    }
}

另外,每次调用函数时,是否必须实例化mysqli？我假设他们不是像程序mysql那样持久的db连接.是的,我知道这是一个范围问题,并且我没有能够理解这个类变量的范围.当我在函数之外声明它时,当我进入函数时它不可用.

UPDATE
如果我改变第12行：

if($stmt = $mysqli -> prepare("SELECT username,email FROM tb_users WHERE username=? OR email=?")) {

至：

$stmt = $mysqli->stmt_init();
    if($stmt = $mysqli -> prepare("SELECT username,email FROM tb_users WHERE username=? OR email=?")) {
        if(!stmt) echo 'Statement prepared'; else echo 'Statement NOT prepared';

我没有准备好声明.现在我更加困惑……

更新：
我联系了我的托管服务提供商,显然支持mySQLi,并且存在mysqlnd驱动程序.也许有一种方法可以简单地测试一下？虽然他们过去通常给我很多知识渊博的答案.

更新…再次：我自己检查了我的服务器功能并发现,而mysqli和PDO存在时,mysqlnd不是.因此,我理解为什么get_result()不起作用(我认为需要mysqlnd),我仍然不明白为什么准备好的语句本身不起作用.

function checkUsernameEmailAvailability($username,$email) {

echo 'pdo about to be created';

$dsn = 'mysql:dbname='.C_BASE.';host='.C_HOST;
$user = C_USER;
$password = C_PASS;

try {
    $dbh = new PDO($dsn,$user,$password);
} catch (PDOException $e) {
    echo 'Connection failed: ' . $e->getMessage();
}

$params = array(':username' => $username,':email' => $email);

try{
$sth = $dbh->prepare('SELECT username,email FROM tb_users WHERE username = :username OR email = :email ');
} catch(PDOException $e) {
    echo 'Prepare failed: ' . $e->getMessage();
}

try{
$sth->execute($params);
} catch(PDOException $e) {
    echo 'Execute failed: ' . $e->getMessage();
}
$result = $sth->fetch(PDO::FETCH_ASSOC);
print_r($result);
}

function checkUsernameEmailAvailability($username,$email) {
    $dsn = 'mysql:dbname='.C_BASE.';host='.C_HOST;
    $user = C_USER;
    $password = C_PASS;
    new PDO($dsn,$password);

    $params = array(':username' => $username,':email' => $email);

    $sth = $dbh->prepare('SELECT username,email FROM tb_users WHERE username = :username OR email = :email ');
    $sth->execute($params);
    $result = $sth->fetch(PDO::FETCH_ASSOC);

    print_r($result);
}