Question

I want to specialize a class template for char, short, long and long long. This specializations should also holds good for the signed and unsigned variants of the integral types.

I know boost library and std::tr1 / C++0x implements is_signed/is_unsigned and make_signed/make_unsigned type_traits. But how can I remove any signed specification from the char type (note: the only integral type where signed itype != itype)?

Answer 1

The “sign-ness” of char is implementation defined. It doesn’t have to be able to store negative numbers. In strict standardese, char even is never a signed integer type, even if it can store negative numbers on an implementation. Still, the class template is_signed will report true for char if it can store negative numbers, because that’s a useful thing for it to do.

Anyway, the boost docs say the following about make_unsigned, making it look like you can use it for your purpose.

If T is a unsigned integer type then the same type as T, if T is an signed integer type then the corresponding unsigned type. Otherwise if T is an enumerated or character type (char or wchar_t) then an unsigned integer type with the same width as T