[C++, CPP] 基本資料型態(Fundamental Data Type)

列舉型態(Enumeration)

• 寫程式時，有時會希望變數的值，只能是特定的指定值之一，此時就要用列舉型態
• 宣告：
  • enum 型別名稱 { 值1, 值2, 值3,.... };
  • enum 型別名稱 { 值1, 值2, 值3,.... } 變數名稱1,變數名稱2,...;
• 匿名宣告：因為沒有定義型別名稱，所以只有在宣告列舉型態時可以宣告變數，之後就無法宣告該型態的變數
  • enum { 值1, 值2, 值3,.... } 變數名稱1,變數名稱2,...;

  • enum  { Sun=5, Mon, Tues, Wed, Thurs, Fri, Sat }　week1;
    week1 = Tues;
    week1 = Week(7);    // 同 week1 = Tues;
    

• 每個列舉型態佔用4bytes
• 列舉子(Enumerator)：列舉型態裡面的值
  • 每個列舉子都會被定義一個整數值，如果沒有指定整數值，則預設是由0開始自動遞增

    • enum Week { Sun, Mon, Tues, Wed, Thurs, Fri, Sat }　week1;
      week1 = Tues;       
      week1 = Week(2);    // 同 week1 = Tues
      

  • 列舉子的值可以重複
  • 預設值1=0，值2=1，值3=2...
  • 若只定義第1個數值，則後序的數值會自動遞增。

    • enum Week { Sun=5, Mon, Tues, Wed, Thurs, Fri, Sat }　week1;
      week1 = Tues;
      week1 = Week(7);    // 同 week1 = Tues;
      

  • 若要用整數值設定列舉型態變數，則要先轉型

    • enum Week { Sun, Mon, Tues, Wed, Thurs, Fri, Sat };
      Week  week1 = Tues;
      Week  week2 = static_cast <week>(2);
      Week week3 = Week(2);