Define enum type in C

Question

How can I define the type of an enum to be uint8 instead of int?

typedef enum
{
  R_DIRECTION_LEFT = 1,
  R_DIRECTION_RIGHT = 2,
  R_DIRECTION_TOP = 4,
  R_DIRECTION_BOTTOM = 8
} R_Direction;

Answer 1

No you can't.

From standard §6.4.4.3 C11 standard N1570

An identifier declared as an enumeration constant has type int.

Answer 2

The identifiers in an enum list have type int, as per §6.7.2.2 3 of the C11 Standard:

The identifiers in an enumerator list are declared as constants that have type int and may appear wherever such are permitted.

But, enumerations constitute distinct types §6.2.5 16:

Each distinct enumeration constitutes a different enumerated type.

Of the enumerated type itself, the Standard says in §6.7.2.2 4 only that:

Each enumerated type shall be compatible with char, a signed integer type, or an unsigned integer type. The choice of type is implementation-defined, but shall be capable of representing the values of all the members of the enumeration.

Further, in a footnote it is pointed out that:

An implementation may delay the choice of which integer type until all enumeration constants have been seen.

So the type of an enumeration is distinct, and this type must be compatible with one of char, a signed integer type, or an unsigned integer type. Which of these will be used is implementation-defined, and may vary from case to case on the same implementation.