A num_put facet that appends a prepends and appends text to an output operation

gistfile1.cpp

#include <locale>

template<class char>
class num_put : public std::num_put<char>
{
    using string_type = std::basic_string<char>;
    
    string_type first_, second_;
public:
    num_put(const string_type& first  = string_type{},
            const string_type& second = string_type{},
            int refs                  = 0)
        : std::num_put<char>(refs)
        , first_(first)
        , second_(second)
    { }
protected:
    iter_type do_put(iter_type out, std::ios_base& str, char_type fill, long v) const;
    iter_type do_put(iter_type out, std::ios_base& str, char_type fill, unsigned long v) const;
private:
    iter_type do_put_impl(iter_type out, std::ios_base& str, char_type fill, long v) const;
};

num_put::iter_type
do_put_impl(iter_type out, std::ios_base& str, num_put::char_type fill, long v) const
{
    num_put::iter_type it = std::copy(first_.begin(), first_.end(), out);
    it = std::num_put<char>::do_put(out, str, fill, v);
    it = std::copy(second_.begin(), second_.end(), out);
    return it;
}

num_put::iter_type
num_put::do_put(num_put::iter_type out, std::ios_base& str, num_put::char_type fill, long v) const
{
    return do_put_impl(out, str, fill, v);
}

num_put::iter_type
num_put::do_put(num_put::iter_type out, std::ios_base& str, num_put::char_type fill, unsigned long v) const
{
    return do_put_impl(out, str, fill, v);
}