Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!usc!wuarchive!udel!princeton!cs!drh
From: drh@cs.Princeton.EDU (Dave Hanson)
Newsgroups: comp.std.c
Subject: Re: enums and bitfields
Message-ID: <2735@rossignol.Princeton.EDU>
Date: 14 Sep 90 20:15:09 GMT
References: <3119@isaak.isa.de>
Organization: Dept. of Computer Science, Princeton University
Lines: 27

In article <3119@isaak.isa.de> gutjahr@isa.de (Bernd Gutjahr) writes:
>1. Is it defined wether bitfield of enum types like in e.g.:
>
>	enum bool { true, false };
>	struct { enum bool flag : 1; } s;
>
>   are signed or not ? As I understand it from K&R, enums behave like ints,
>   and the sign of sign of int bitfield are implementation-dependent.

according to sec. 3.5.2.1, bit-fields must be int, signed int, or unsigned.
each enum must be compatible with an integer type (sec. 3.5.2.2); if that
type is int, signed int, or unsigned, then the enum is a legal
bit-field type. otherwise it's illegal.

since compilers are free to use different integer types for enums,
using enum bit-fields make your program compiler-dependent.

>2. If enums behave like ints, does this means that either
>	- int and enum bitfield are signed
>	- int and enum bitfield are unsigned
if the enum is compatible with int, the bit-field is signed;
if the enum is compatible with unsigned, the bit-field is unsigned.

>4. If the behavior of enum bitfields is implementation dependent,
>   is it possible the make them unsigned with something like:
>	unsigned enum bool flag : 1;
no.