提供了未定义的变量和无效的参数

Question

如果我从下拉菜单中选择一个学生（如果$_POST['student'] != 0值为0代表All选项，并且所有其他选项都有自己的数字），那么这很奇怪ubt，我得到一个错误，说明：

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

我的问题是什么原因造成这个错误，怎么能解决吗？

代码如下，我曾试图降低尽可能靠近代码片段的底部就是错误行是被注释掉：

$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>'; 
    } 
    } 

Answer 1

的变量$问题本身可能是初始化问题。仔细查看你的代码，看看$questions =被调用的地方。可能每次都是在没有运行的情况下发言。

如果您拨打：

$questions[...] 

，从不初始化$questions作为数组你也会有问题。 所以，你需要初始化$questions：在此之后

$questions = array(); 

你不会有任何问题，访问数组的领域。