c++ - POD的默认析构函数是静态的吗？

Question

我正在使用/Wall 进行编译，并收到警告 C4100: 'ptr' : unreferenced formal parameter warning 。该警告似乎是由调用 MSVC 的 std::_Container_proxy 上的析构函数引起的。 ，它有一个默认的析构函数。

我的代码:

template<class T>
class linear_allocator {
    //...other declarations...
    static void destroy(pointer ptr);
};
//...other definitions...
template<class T>
inline void linear_allocator<T>::destroy(typename linear_allocator<T>::pointer ptr)
{
    ptr->~T(); //line 262.  warning C4100: 'ptr' : unreferenced formal parameter
}
//ironically, this isn't a test case, this is my actual thingy class.  Go figure.
struct thingy { 
    unsigned int DATA;
    thingy() : DATA(0xABCDEF) {}
    ~thingy() {assert(DATA == 0xABCDEF);}
};
int main() {
    typedef std::vector<thingy, linear_allocator<thingy>> thingyholder;
    std::vector<thingyholder> holder;
}

警告全文为:

      f:\code\utilities\linear_allocator\linear_allocator.h(261): warning C4100: 'ptr' : unreferenced formal parameter
      f:\code\utilities\linear_allocator\linear_allocator.h(262) : while compiling class template member function 'void linear_allocator<T>::destroy(std::_Container_proxy *)'
      with
      [
          T=std::_Container_proxy
      ]
      f:\code\utilities\linear_allocator\linear_allocator.h(178) : while compiling class template member function 'linear_allocator<T>::~linear_allocator(void) throw()'
      with
      [
          T=std::_Container_proxy
      ]
      c:\program files\microsoft visual studio 10.0\vc\include\vector(454) : see reference to class template instantiation 'linear_allocator<T>' being compiled
      with
      [
          T=std::_Container_proxy
      ]
      c:\program files\microsoft visual studio 10.0\vc\include\vector(452) : while compiling class template member function 'std::_Vector_val<_Ty,_Alloc>::~_Vector_val(void)'
      with
      [
          _Ty=thingy,
          _Alloc=linear_allocator<thingy>
      ]
      c:\program files\microsoft visual studio 10.0\vc\include\vector(481) : see reference to class template instantiation 'std::_Vector_val<_Ty,_Alloc>' being compiled
      with
      [
          _Ty=thingy,
          _Alloc=linear_allocator<thingy>
      ]
      c:\program files\microsoft visual studio 10.0\vc\include\vector(1307) : see reference to class template instantiation 'std::vector<_Ty,_Ax>' being compiled
      with
      [
          _Ty=thingy,
          _Ax=linear_allocator<thingy>
      ]
      c:\program files\microsoft visual studio 10.0\vc\include\vector(1301) : while compiling class template member function 'void std::vector<_Ty>::_Tidy(void)'
      with
      [
          _Ty=thingyholder
      ]
      f:\code\utilities\linear_allocator\main.cpp(71) : see reference to class template instantiation 'std::vector<_Ty>' being compiled
      with
      [
          _Ty=thingyholder
      ]

我看到它正在使用 std::_Container_proxy 的析构函数，这很简单:

struct _Container_proxy
{   // store head of iterator chain and back pointer
_Container_proxy()
    : _Mycont(0), _Myfirstiter(0)
    {   // construct from pointers
    }

const _Container_base12 *_Mycont;
_Iterator_base12 *_Myfirstiter;
};

根据MSVC C4100: 'application' : unreferenced formal parameter warning ，这可能会发生 if The functions you are calling using the application object are static functions, so they aren't really referencing the application object. 。 std::_Container_proxy看起来是一个 POD，这是否意味着默认析构函数是静态的作为优化？

(是的，我知道各种解决方法可以使警告消失。我想在输入 ptr=ptr; //warning workaround 之前确定为什么会收到警告。)

Answer 1

这是 Visual C++ 中的一个已知错误:"Visual C++ gives unexpected warning C4100 on explicit call to object destructor" .

可以安全地忽略该警告(或通过#pragma warning或/Wd4100抑制)。