在另一個類中使用受保護的析構函數刪除對象

Question

我知道此問題之前在此處詢問過：Delete an object with a protected destructor。但是，該解決方案對我無效。在編譯過程中我仍然遇到錯誤。

我的項目也是創建一個智能指針，一些測試讓我用受保護的析構函數刪除對象（有些是虛擬的，有些不是），這會導致編譯時錯誤。

我真的不知道從哪裏開始解決這個問題。先謝謝你！

這是我必須做的想法：

#include <cstddef> 

template<typename T> void DefaultDeleter(void *p) { delete static_cast<T*>(p); } 

struct ref_counter { 
    int refs; 
    void *p; 
    void (*d)(void *); 
}; 

template<typename T> class Sptr { 
    public: 
      Sptr(T *obj){ 
      c = new ref_counter; 
      c->refs = 1; 
      c->p = static_cast<void*>(obj); 
      c->d = &DefaultDeleter<T>; 
      p = p; 
     } 
     void reset(){ 
      (c->d)(c->p); 
      delete c; 
     } 
    private: 
     T *p; 
     ref_counter *c; 
}; 

class Base{ 
    public: 
     Base(){ 
      atr = new int(1); 
     } 
    protected: 
     ~Base(){ 
      delete atr; 
     } 
    private: 
     int *atr; 
}; 

int main(){ 
    Base b1; 
    Sptr<Base> s1(&b1); 
    return 0; 
} 

該代碼產生此錯誤：

root@resnet-230-99:~/cs440/a3# g++ test.cpp -o test 
test.cpp: In function ‘int main()’: 
test.cpp:43:7: error: ‘Base::~Base()’ is protected within this context 
    Base b1; 
     ^~ 
test.cpp:35:3: note: declared protected here 
    ~Base(){ 
^
test.cpp: In instantiation of ‘void DefaultDeleter(void*) [with T = Base]’: 
test.cpp:17:9: required from ‘Sptr<T>::Sptr(T*) [with T = Base]’ 
test.cpp:44:19: required from here 
test.cpp:3:53: error: ‘Base::~Base()’ is protected within this context 
template<typename T> void DefaultDeleter(void *p) { delete static_cast<T*>(p); } 
                ^~~~~~ 
test.cpp:35:3: note: declared protected here 
    ~Base(){ 

Answer 1

的事情是，你的構造需要可以摧毀真正的類型，即使基類的析構函數是受保護的，是這樣的：

template<typename T> 
class Sptr { 
public: 
    template <typename U> 
    explicit Sptr(U* obj){ 
     c = new ref_counter; 
     c->refs = 1; 
     c->p = static_cast<void*>(obj); 
     c->d = &DefaultDeleter<U>; 
    } 
// ... 
}; 

然後用：

class Base { 
protected: 
    ~Base() = default; 
}; 

class Derived : public Base 
{ 
public: 
    ~Derived() = default; 
}; 

你可以做

Sptr<Base> p{new Derived()};