static_label.cpp

#include <assert.h>

#include <cstring>
#include <algorithm>
#include <iostream>
#include <type_traits>

template<std::size_t N>
class label
{
public:
  label() = default;

  void set_text(const char *str)
  {
    std::size_t size = std::strlen(str);
    assert(size < N);
    std::copy_n(str, size, static_cast<char*>(m_str));
  }

  const char* get_text() const
  {
    return m_str;
  }

  std::size_t get_max_size() const
  {
    return N;
  }

private:
  char m_str[N];
};

template<std::size_t N, typename... Ts>
struct label<N> make_label(const char (&str)[N], Ts&&... args)
{
  label<N> label{std::forward<Ts>(args)...};
  label.set_text(str);

  return label;
}

int main()
{
  auto lbl = make_label("My Label");

  std::cout << "length of label '" << lbl.get_text() 
    << "': " << lbl.get_max_size() << std::endl;

  lbl.set_text("Very, very long label");

  return 0;
}