std::basic_string::operator basic_string_view

#include <iostream>
#include <string>
#include <string_view>
 
void show_wstring_size(std::wstring_view wcstr_v)
{
  std::cout << wcstr_v.size() << " code points\n";
}
 
int main()
{
  std::string cppstr = "ラーメン";   // narrow string
  std::wstring wcstr = L"ラーメン";  // wide string
 
  // Implicit conversion from string to string_view
  // via std::string::operator string_view:
  std::string_view cppstr_v = cppstr;
 
  std::cout << cppstr_v << '\n'
            << cppstr_v.size() << " code units\n";
 
  // Implicit conversion from wstring to wstring_view
  // via std::wstring::operator wstring_view:
  show_wstring_size(wcstr);
 
  // Warning:
  // It is the programmer's responsibility to ensure that std::string_view 
  // does not outlive the pointed-to string! 
 
  std::string_view BAD(std::string("a temporary string")); // holds a dangling pointer!
}