無法刪除我的自定義類（C++）的堆實例

Question

下面是我得到了什麼：

class MyClass { 
    int holder; 
public: 
    MyClass() { 
     holder = 5; 
    } 
}; 

---

template<class T> 
class First { 
    std::vector<T> items; 
public: 
    First() { 
     T* tmp; 
     for (int i = 0; i < 20; i++) { 
      tmp = new T(); 
      items.push_back(*tmp); 
     } 
    }; 
    ~First() { 
     for (int i = 0; i < 20; i++) { 
      delete items.at(i); 
     } 
    }; 
}; 

---

class Second { 
    std::vector<std::deque<First<MyClass>>> items; 
public: 
    Second() { 
     std::deque<First<MyClass>>* tmp; 
     for (int i = 0; i < 10; i++) { 
      tmp = new std::deque<First<MyClass>>; 
      items.push_back(*tmp); 
     } 
    }; 
    ~Second() { 
     for (int i = 0; i < 10; i++) { 
      for (int j = 0; j < items.at(i).size(); j++) { 
       delete items.at(i).at(j); // this deletes the "First" instances 
      } 
      delete items.at(i); // this deletes the deque 
     } 
    }; 
}; 

---

在我main，我創建了一個Second的實例並將First實例添加到它（thro呃方法不包括在內）。在main的末尾，我刪除了Second的實例，該實例應刪除First和deques的所有實例。然而，我發現了以下錯誤：

error: cannot delete expression of type 'value_type' (aka 'MyClass') 
error: cannot delete expression of type 'value_type' (aka 'First<MyClass>') 
error: cannot delete expression of type 'value_type' (aka 'std::deque<First<MyClass>>') 

從本質上講，我所有的delete命令引發錯誤。我在這裏錯過了什麼？我需要手動實現析構函數，因爲我在堆上創建了一堆東西 - 對嗎？

Answer 1

你永遠不會存儲new表達式的結果。您的代碼也許應該是這樣的：

First() { 
    T* tmp; 
    for (int i = 0; i < 20; i++) { 
     tmp = new T(); 
     items.push_back(*tmp); 
     delete tmp;    // result of "new" is still accessible here 
    } 
} 

~First() { } 

或者這樣：

First() { 
    for (int i = 0; i < 20; i++) { 
     items.push_back(T()); 
    } 
} 

或者只是這樣的：

First() : items(20) {}