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如果我从下拉菜单中选择一个学生，这很奇怪（如果$_POST['student'] != 0as 值0代表一个All选项，而所有其他选项都有自己的数字），我收到一条错误消息：

Notice: Undefined variable: questions in ... on line 597 Warning: Invalid argument supplied for foreach() in ... on line 597

我的问题是导致此错误的原因以及如何解决？

下面的代码是我试图尽可能减少的代码，靠近代码片段的底部是错误行的注释：

    $selectedstudentanswerqry = "
        SELECT
        sa.StudentId, StudentAlias, StudentForename, StudentSurname
    ...
        FROM Student st
    ...
        ";

        // Initially empty
            $where = array('q.SessionId = ?');
            $parameters = array($_POST["session"]);
            $parameterTypes = 'i';


        //check if POST is empty

        // Check whether a specific student was selected

        $p_student = empty($_POST["student"])?0:$_POST["student"];  // Now if $_POST['student'] is either 0 or empty $p_student will be 0
        switch($p_student){
        case 0:
            //dont' add where filters
            break;
        default:
            $where[] = 'sa.StudentId = ?';
            $parameters[] .= $_POST["student"];
            $parameterTypes .= 'i';
        }

        // Check whether a specific question was selected
        $p_question = empty($_POST["question"])?0:$_POST["question"]; // Same here, if $_POST['question'] is either 0 or empty $p_question will be 0
            switch($p_question){
        case 0:
            //dont' add where filters 
            break;
        default:
            $where[] = 'q.QuestionId = ?';
            $parameters[] .= $_POST["question"];
            $parameterTypes .= 'i';
        }
        // If we added to $where in any of the conditionals, we need a WHERE clause in
        // our query
        if(!empty($where)) {
            $selectedstudentanswerqry .= ' WHERE ' . implode(' AND ', $where);
            // You only need to call bind_param once
    }




        $selectedstudentanswerqry .= "
          GROUP BY sa.StudentId, q.QuestionId
          ORDER BY StudentAlias, q.SessionId, QuestionNo
        ";


    global $mysqli;
    $selectedstudentanswerstmt=$mysqli->prepare($selectedstudentanswerqry);

    if (count($where) == 1) {
            $selectedstudentanswerstmt->bind_param($parameterTypes, $parameters[0]);
        }
        else if (count($where) == 2) {
            $selectedstudentanswerstmt->bind_param($parameterTypes, $parameters[0], $parameters[1]);
        }
        else if (count($where) == 3) {
            $selectedstudentanswerstmt->bind_param($parameterTypes, $parameters[0], $parameters[1], $parameters[2]);
        }

    // get result and assign variables (prefix with db)
    $selectedstudentanswerstmt->execute(); 
    $selectedstudentanswerstmt->bind_result($detailsStudentId,$detailsStudentAlias,$detailsStudentForename,$detailsStudentSurname); 

    $selectedstudentanswerstmt->store_result();
    $selectedstudentanswernum = $selectedstudentanswerstmt->num_rows(); 

        $arrStudentId = array();
        $arrStudentAlias = array();
     ...

        while ($selectedstudentanswerstmt->fetch()) {

        //Check if the student data exist.
        if (!isset($questions[$detailsStudentId])) {
            $questions[$detailsStudentId] = array(
                'studentalias' => $detailsStudentAlias,
                'studentforename' => $detailsStudentForename,
                'studentsurname' => $detailsStudentSurname,
                'questions' => array()
            );
        }

        $questions[$detailsStudentId]['questions'][$detailsQuestionId] = array(
            'questionno'=>$detailsQuestionNo,
            'content'=>$detailsQuestionContent,
    .....
        );
    }

    $selectedstudentanswerstmt->close();
    ?>

//LINE 597 ERROR BELOW
    foreach ($questions as $studentId => $studentData) {
        echo '<hr><h3>'.$studentData['studentalias'].' - '.$studentData['studentforename'].' '.$studentData['studentsurname'].'</h3>';

        foreach ($studentData['questions'] as $questionId => $questionData) {
            echo '<h3>'.$questionData['questionno'].': '.$questionData['content'].'</h3>';
    }
    }
4

1 回答 1

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变量 $questions 本身的初始化可能是问题所在。查看您的代码，看看在哪里$questions =调用了类似的东西。可能每次都在未运行的 if 语句中。

如果你打电话：

$questions[...]

并且永远不会初始化$questions为数组，您也会遇到问题。所以你需要初始化$questions：

$questions = array();

在此之后，您将没有问题访问数组的字段。

于 2013-02-19T17:29:25.077 回答