Question

C ++中是否可以确定变量的类型是指针还是任何带有重载operator*的迭代器？

有标准的std::is_pointer，但它没有说明迭代器。

我想在这样的代码中使用它：

template<class T>
void func(T var)
{
    if constexpr (can_be_dereferenced<T>::value)
    {
        // do something with *var;
    }
}

Answer 1

您基本上想检查Sub Delete_EntireColumn() Dim LCol as Long, LRow as Long, i as Long With Workbooks(REF).Sheets(REF) LCol = .Cells(1, .Columns.Count).End(xlToLeft).Column For i = LCol To 1 Step - 1 LRow = Application.WorksheetFunction.CountA(.Columns(i)) If LRow < 30 Then .Columns(i).EntireColumn.Delete End If Next i End With End Sub是否有效。这是SFINAE检查的理想用例：

*var

Answer 2

您可以使用编译时函数重载分辨率和SFINAE来做到这一点：

template<class T, typename = std::enable_if_t<std::is_pointer<T>::value>>
void func(T var)
{
  // a pointer
}

template<class T, typename = std::enable_if_t<!std::is_pointer<T>::value>,
         typename = T::value_type>
void func(T var)
{
  // possibly an iterator
}

int main()
{
  int *i = new int(11);
  func(i); // Calls the first overload

  std::vector<int> v;
  std::vector<int>::const_iterator it = v.begin();

  func(it); // Calls the second overload

  func(2); // Fail, as there is no function for this argument.
  [..]

如何检查给定类型的变量是否可以取消引用？

2 个答案: