訪問關聯數組：爲什麼這個（可能是不正確的）代碼工作？

Question

問題：

在第二（以下）的代碼段，在內foreach循環（也就是foreach循環嵌套在另一個foreach循環），則$value對應於$studentCoursesStudied的元件，而不是$studentCoursesStudied數組本身，對吧？

的correct way訪問$studentCoursesStudied陣列的元素的值將是：

$studentCoursesStudied[$key] 

但是他們正在訪問像

$value['an-element-name/key'] 

其中$studentCoursesStudied陣列的每個元素的值$ value對應於數組的一個元素，而不是數組本身！爲什麼？

背景： 我讀通過別人學習寫一個PHP腳本，我不明白他們是如何在一個點訪問關聯數組中的值。所以我寫了這個示例代碼來問這個問題。

這是Student類，學生有一個包含關聯數組的名稱爲recordCoursesStudied的屬性。

class Student { 
    public $studentName; 
    public $studentAge; 
    public $studentCoursesStudied = null; 

    function __construct($studentName, $studentGpa) { 
     $this->studentName = $studentName; 
     $this->studentGpa = $studentGpa; 
    } 

    function recordCoursesStudied ($courseName, $courseNumber, $creditHours, $maxMarks, $courseType) { 
     $this->studentCoursesStudied[] = array(
      'courseName' => $courseName; 
      'courseNumber' => $courseNumber; 
      'creditHours' => $creditHours; 
      'maxMarks' => $maxMarks; 
      'courseType' => $courseType; 
     ); 
    } 
} 

然後我們想從另一個類Whatever從它的方法newCourseRecord訪問recordCoursesStudied的元素。

注：在塊註釋內foreach循環之後，我已經寫了相同的片段，以更好的名稱來把事情說清楚。

class Whatever { 
    private $students; 
    private $currentStudent; 

    function __construct() { 
     $this->newStudent('Zarah', 3.4); 
     $this->newCourseRecord('DBMS', 'BR223', 3, 100, 'Core'); 
     $this->doTheWork(); 
    } 

    function newStudent($studentName, $studentGpa) { 
     $this->students[$studentName] = new Student($studentName, $studentGpa); 
     $this->currentStudent = $studentName; 
    } 

    function newCourseRecord($courseName, $courseNumber, $creditHours, $maxMarks, $courseType) { 
     $this->students[$this->studentName]->recordCoursesStudied($courseName, $courseNumber, $creditHours, $maxMarks, $courseType); 
    } 

    function doTheWork() { 
     ... 
     foreach ($this->students as $key=>$value) { 
      ... 
      foreach($value->studentCoursesStudied as $key=>$value) { /****************************/ 
       ... 
       //Echo each property of $studentCoursesStudied. 
       someOtherFunction($value['courseName'], $value['courseNumber'], $value['creditHours'], $value['maxMarks'], $value['courseType']); 
       ... 
      } 
      ... 
     } 
     /*foreach ($this->students as $studentKey=>$studentValue) { 
      ... 
      foreach($studentValue->studentCoursesStudied as $courseKey=>$courseValue) { /****************************/ 
       ... 
       //Echo each property of $studentCoursesStudied. 
       /*someOtherFunction($courseValue['courseName'], $courseValue['courseNumber'], $courseValue['creditHours'], $courseValue['maxMarks'], $courseValue['courseType']); 
       ... 
      } 
      ... 
     }*/ 
     ... 
    } 

} 

在給定的代碼，在foreach環路由*的要點之外，他們已經通過執行類似訪問的Student::studentCoursesStudied數組中的值：

$value-of-an-element-in-array['key-of-an-element-in-array'] 

但不應關聯的元素數組訪問像name-of-array['key-of-an-element-in-array']？

Answer 1

確定方法recordCoursesStudied不是這個樣子的？

$this->studentCoursesStudied[] = array(
     'courseName' => $courseName; 
     'courseNumber' => $courseNumber; 
     'creditHours' => $creditHours; 
     'maxMarks' => $maxMarks; 
     'courseType' => $courseType; 
    ); 

這將是有意義如果studentCoursesStudied用有關多個課程的信息的陣列（和每個數組項是描述單個當然字段的數組）。那麼你的嵌套foreach將有意義，除了你不能使用$ key和$ value作爲循環變量。

Answer 2

您構建一流的，比你在循環

foreach ($this->students as $key=>$value) { 
     ... 
     foreach($value->studentCoursesStudied as $key=>$value) { /****************************/ 
      ... 
      //Echo each property of $studentCoursesStudied. 
      someOtherFunction($value['courseName'], $value['courseNumber'], $value['creditHours'], $value['maxMarks'], $value['courseType']); 
      ... 
     } 
     ... 
    } 

這是正確的訪問值

$this->students[$studentName] = new Student($studentName, $studentGpa); 

設置的值比

function newCourseRecord(
       $courseName, 
       $courseNumber, 
       $creditHours, 
       $maxMarks, 
       $courseType) { 
        $this->students[$this->studentName]->recordCoursesStudied(
          $courseName, 
          $courseNumber, 
          $creditHours, 
          $maxMarks, 
          $courseType); 
} 

。

Answer 3

嘗試如下：

class Student { 
private $studentName; 
private $studentAge; 
private $studentCoursesStudied = null; //private not run out this class so you can define a public function to get it 

public function getStudentCoursesStudied() { 
    return $this -> $studentCoursesStudied; 
} 

function __construct($studentName, $studentGpa) { 
    $this->studentName = $studentName; 
    $this->studentGpa = $studentGpa; 
} 

function recordCoursesStudied ($courseName, $courseNumber, $creditHours, $maxMarks, $courseType) { 
    $this->studentCoursesStudied = array(
     'courseName' => $courseName; 
     'courseNumber' => $courseNumber; 
     'creditHours' => $creditHours; 
     'maxMarks' => $maxMarks; 
     'courseType' => $courseType; 
    ); 
} 
} 


class Whatever { 
private $students = array(); // define is a empty array(); 
private $currentStudent; 

function __construct() { 
    $this->newStudent('Zarah', 3.4); 
    $this->newCourseRecord('DBMS', 'BR223', 3, 100, 'Core'); 
    $this->doTheWork(); 
} 

function newStudent($studentName, $studentGpa) { 
    $this->students[$studentName] = new Student($studentName, $studentGpa); 
    $this->currentStudent = $studentName; 
} 

function newCourseRecord($courseName, $courseNumber, $creditHours, $maxMarks, $courseType) { 
//you use $this -> studentName but i n't find where's defined i think you want to use $this -> currentStudent 
    $this->students[$this-> currentStudent]->recordCoursesStudied($courseName, $courseNumber, $creditHours, $maxMarks, $courseType); 
} 

function doTheWork() { 
    ... 
    foreach ($this->students as $key=>$value) { 
     ... 
     foreach($value-> getStudentCoursesStudied() as $key=>$value) { /****************************/ 
      ... 
      //Echo each property of $studentCoursesStudied. 
      someOtherFunction($value['courseName'], $value['courseNumber'], $value['creditHours'], $value['maxMarks'], $value['courseType']); 
      ... 
     } 
     ... 
    } 
    /*foreach ($this->students as $studentKey=>$studentValue) { 
     ... 
     foreach($studentValue->studentCoursesStudied as $courseKey=>$courseValue) { /****************************/ 
      ... 
      //Echo each property of $studentCoursesStudied. 
      /*someOtherFunction($courseValue['courseName'], $courseValue['courseNumber'], $courseValue['creditHours'], $courseValue['maxMarks'], $courseValue['courseType']); 
      ... 
     } 
     ... 
    }*/ 
    ... 
} 

}