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Re: A bit field's length

From: Ian Lance Taylor <iant at google dot com>
To: kum <a dot kumaresh at gmail dot com>
Cc: gcc-help at gcc dot gnu dot org
Date: 21 Nov 2007 07:57:49 -0800
Subject: Re: A bit field's length
References: <302c6e640711210412v6e36597p447309b93ea1213d@mail.gmail.com>

kum <a.kumaresh@gmail.com> writes:

> On a 32 bit platform,
> Is this structure legal?
> 
> struct
> {
> UINT64 part1 : 48;
> UINT64 part2 : 16;
> }Parts;

gcc accepts that.  It is not portable C--the C99 standard only
requires the compiler to support bitfields of type _Bool, int, or
unsigned int.

> Do I have to tune the compiler to pack them into a single 64 bit
> space?

No.

> While assigning some 32 bit value to Parts.part1, do I have to
> cast the r-value into UINT64?

No, the cast will happen automatically.

Ian

References:
- A bit field's length
  - From: kum

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