无法删除我的自定义类的堆实例(C++)

Question

这是我得到的:

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,我正在创建一个实例Second并向其添加First实例(通过未包含的方法).在年底main,我删除的情况下Second,应删除的所有实例First和deques.但是,我收到以下错误:

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>>')

基本上,我的所有delete命令都抛出错误.我在这里错过了什么？我需要手动实现析构函数,因为我在堆上创建了一堆东西 - 对吗？

Answer 1

您永远不会存储new表达式的结果.您的代码应该如下所示:

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() { }

或者像这样:

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

或者像这样:

First() : items(20) {}