Traits for character underlying types

From: Daryle Walker (darylew_at_[hidden])
Date: 2001-02-20 14:48:14

The "char" type is supposed to be like either "signed char" or "unsigned
char," which one is implementation defined.  Similarly, the "wchar_t" type
is supposed to be like one of the other integral types, which one is
implementation defined.  Could we have some sort of structure indicating
those types' base types?  I guess it would be something like:

//==========================================================================
template <typename T> struct underlying_type;

template <>
struct underlying_type<char>
{
    typedef something  base_type;
};

// The following should be macro-blocked for compilers that don't have
// a separate "wchar_t" type.

template <>
struct underlying_type<wchar_t>
{
    typedef something  base_type;
};

// Should there be a general version of this template?  If so, I guess that
// the those T types should map to themselves.

// We don't have to do class templates, maybe macro magic will do:
#if SOMETHING
typedef signed char  char_underlying_type
#else
typedef unsigned char  char_underlying_type
#endif

#if HAVE_INTRINSIC_WCHAR_T
#if SOMETHING
typedef signed char  wchar_t_underlying_type
#elif SOMETHING_ELSE
typedef unsigned char wchar_t_underlying_type
//...
#else
typedef unsigned long long  wchar_t_underlying_type
#endif
#endif
//==========================================================================

How would we figure out the types?  I guess something using <climits> macros
and/or comparisons from <limits> values would be used.  What header would
this go under, "type_traits.hpp" or a new one?

-- 
Daryle Walker
Mac, Internet, and Video Game Junkie
darylew AT mac DOT com