Xref: utzoo comp.std.c:4040 comp.std.c++:493
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From: rfg@lupine.ncd.com (Ron Guilmette)
Newsgroups: comp.std.c,comp.std.c++
Subject: A question on bit-field widths.
Message-ID: <3028@lupine.NCD.COM>
Date: 17 Dec 90 22:10:36 GMT
Sender: rfg@NCD.COM
Followup-To: comp.std.c
Organization: Network Computing Devices, Inc., Mt. View, CA
Lines: 44

I am posting this question to both comp.std.c and comp.std.c++ because
the question arises for both languages.

Given a machine on which 'long int' is 32 bits and `short int' is 16 bits,
what should the following program print?  Should this program even be
allowed to compile without errors?


struct S1 {
	long	field:33;
};

struct S2 {
	short	field1:17;
	short	field2:17;
	int	field3;
	short	field4:17;
};

extern printf (const char *, ...);

struct S1 s1;
struct S2 s2;

int main ()
{
  printf ("sizeof (struct S1) = %d\n", sizeof (struct S1));
  printf ("sizeof (struct S2) = %d\n", sizeof (struct S2));

  s2.field1 = 0x3FFFF;
  s2.field2 = 0x3FFFF;
  s2.field4 = 0x3FFFF;

  printf ("field1 = %d, field2 = %d, field3 = %d\n",
    s2.field1, s2.field2, s2.field3);

  return 0;
}

As usual, it would be helpful if someone could point me at the appropriate
parts of the C standard (or Annotated C++ Reference Manual) where such
questions are answered.

Thanks.