Thread: PLZZZZZZ need help on bit fileds

here is the structures for date, time and attribute
suppose that there are the date( 2 bytes ), time( 2 bytes ) and attribute( 1 byte ) stored somewhere inside array of buffer.
here is the attribute:
Flags in the Attribute byte
7 6 5 4 3 2 1 0
Reserved A D V S H R 0000h

here is the time:
The field is in the special format described below:

Time Format
15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
Hours (0-23) Minutes (0-59) Seconds (0-29) 0000h
Seconds are counted with 2 seconds interval, so a value of 29 in this field gives 58 seconds.

here is the date:
The field is in the special format described below:

Date Format
15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
Years from 1980 Month of year (1-12) Day of month (1-31) 0000h

any one know how to use bit fileds?

my question is how do i get the date( 2 bytes ), time( 2 bytes ) and attribute( 1 byte ), because they have different length of bits
i mean each data that i want in these three structures.

or is there any othere way to these three things

PLzzz help me out

if u need more info, plz post here.

Code:

typedef struct                
{
	unsigned	two_secs : 5;	/* low 5 bits: 2-second increments */
	unsigned	minutes : 6;	/* middle 6 bits: minutes */
	unsigned	hours : 5;		/* high 5 bits: hours (0-23) */
}DosTime;				/* 2 bytes total */

typedef struct             
{
	unsigned	date : 5;		/* low 5 bits: date (1-31) */
	unsigned	month : 4;		/* middle 4 bits: month (1-12) */
	unsigned	year : 7;		/* high 7 bits: year - 1980 */
}DosDate;				/* 2 bytes total */

typedef struct                 
{
	unsigned	int	read_only : 1;	/* b0 */
	unsigned	int	hidden : 1;
	unsigned	int	system : 1;
	unsigned	int	volume_label : 1;
	unsigned	int	directory : 1;
	unsigned	int	archive : 1;
	unsigned	int	reserved : 2;	/* b6, b7 */
}Attrib;

The time and date fields use the following "packed" storage format:

Packed Time:

15:11 - > Hour
10:5 - > Minute
4:0 - > Second / 2


Packed Date:

15:9 - > Year ¡V 1980
8:5 - > Month
4:0 - > Day

Attribute:
7:6 - > Reserved
5 - > A
4 - > D
3 - > V
2 - > S
1 - > H
0 - > R

Not sure what you want

DosDate now;

now.date = 4;
now.month = 7;
now.year = 2002 - 1980;

The notation for accessing them is exactly the same as for normal structure members


> stored somewhere inside array of buffer.
Perhaps
memcpy ( &now, &buff[pos], sizeof(now) );

It's very unclear what you are looking for! From what I've understood, you can go about this way:

Code:

struct _buffer
{
            short int s_date;    /*   2 Bytes of DATE   */
            short int s_time;    /*   2 Bytes of TIME   */
            char        attr;    /*   1 Byte of Attribute   */
}buffer;

...

fn()
{
           date_1_bit  = buffer.s_date & (1 << 1);
           date_7_bit  = buffer.s_date & (1 << 7);

           time_2_bit  = buffer.s_time & (1 << 2);
           time_15_bit = buffer.s_time & (1 << 15);
}

>any one know how to use bit fileds?

A bitfield is a struct where each member consists of 1 or more bits. This is useful for a lot of cases. For example if you want to access the individual bits of a byte easily without having to deal with bitshifting, bitmasks and that kind of techniques.

Code:

/* This is an example of how to define a bitfield which can be used to access bits of a byte individually. */
typedef 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;
} byte_bitfield;

/* This function demonstrates how to access the individual bits. */
void function ()
{
    byte_bitfield byte;

    /* set first bit of byte to 0 */
    byte.b0 = 0;
    /* set second bit of byte to 1 */
    byte.b1 = 1;
}