std::basic_ios<CharT,Traits>::narrow (3) - Linux Manuals
char narrow( char_type c, char dfault ) const;
Converts a current locale-specific character c to its standard equivalent. The result is converted from char_type to char if needed. If no conversion can be performed, the function returns dfault.
Effectively calls std::use_facet< std::ctype<char_type> >(getloc()).narrow(c, dfault);.
c - character to convert
dfault - character to return if the conversion was unsuccessful
Character converted to its standard equivalent and then to char. dfault is returned if the conversion fails.
widen (public member function)
narrow (public member function of std::ctype<CharT>)