From:	"Tim Nicholson" <T DOT J DOT Nicholson AT btinternet DOT com>
Newsgroups:	comp.os.msdos.djgpp
Subject:	Re: Bit field query
Date:	Thu, 4 Oct 2001 21:21:44 +0100
Organization:	Skyforce avionics Limited
Lines:	79
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References:	<9pidst$kgu$1 AT epos DOT tesco DOT net>
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To:	djgpp AT delorie DOT com
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B0 is the LSB and apears in the leftmost bit of the 32 bit field. The
following program will prove this.

Tim

//Compile this to show the bit field.

struct bit_field
{
unsigned int b0 : 1;
unsigned int b1 : 1;
unsigned int b2 : 1;
unsigned int b3 : 1;
unsigned int b4 : 1;
unsigned int b5 : 1;
unsigned int b6 : 1;
unsigned int b7 : 1;
};

int main(void)
{
struct bit_field my_bits;
unsigned int *my_word;
short int i;

my_word = (unsigned int *) &my_bits;

*my_word = 0;

my_bits.b0 = 1;
my_bits.b5 = 1;
for (i=0; i<32;i++)
   {
   printf("%d", (*my_word) & 0x80000000 ? 1:0);
   *my_word <<= 1;
   }
printf("\n");
}
"Graham Warren" <Moosehead AT tesco DOT net> wrote in message
news:9pidst$kgu$1 AT epos DOT tesco DOT net...
> I have a question about bit-fields.
>
> In a program I have defined a bit-field using the code shown below.
>
>
> /* define bit-field */
>
> struct {
> unsigned int b0 : 1;
> unsigned int b1 : 1;
> unsigned int b2 : 1;
> unsigned int b3 : 1;
> unsigned int b4 : 1;
> unsigned int b5 : 1;
> unsigned int b6 : 1;
> unsigned int b7 : 1;
> } bit_field;
>
> /* */
>
>
>
> My questions are: would bit_field.b0 be the furthest left or furthest
right
> bit if the byte is written out 00000000?
> Would this change if more bits were defined in the bit field to make it
> spill over into a larger than 1 byte area?
>
> Also which bit in 00000000 is referred to as the most-significant and
which
> is the least-significant?
>
>
> Thankyou
> Graham Warren
>
>

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