C++ 中变量的限定符

Question

How do I know if qualifiers like const etc are associated with the passed arguments to a function?

eg

template<class T>
void callback(T & data)
{
  body of function
}

How do I know if the data is const etc?

Answer 1

You can test whether a type (including a template type argument) is const qualified using a standard type trait:

bool is_const = std::is_const_v<T>;

If T is const qualified, then and only then is T& a reference to const.

Whether or not the referred object is const is something that cannot be inspected.