std::num_put::~num_put

From Cppreference

Destructs a std::num_put facet. This destructor is protected and virtual (due to base class destructor being virtual). An object of type std::num_put, like most facets, can only be destroyed when the last std::locale object that implements this facet goes out of scope or if a user-defined class is derived from std::num_put and implements a public destructor.

[edit] Example

#include <iostream>
#include <locale>
struct Destructible_num_put : public std::num_put<wchar_t>
{
    Destructible_num_put(std::size_t refs = 0) : num_put(refs) {}
    ~Destructible_num_put() {}; // public dtor
};
int main()
{
    Destructible_num_put dc;
    // std::num_put<wchar_t> c;  // compile error: protected destructor
}