This article includes bitfield structure
examples.

Please, read it :  BITFIELDS

 
About structure bit1

struct bitfield1

{

unsigned int a:6;

unsigned int b:6;

unsigned int c:6;

char d:8;

} bit1;




 bit1.a=5;

 bit1.b=14;                              

  bit1.c=6;

  bit1.d=9;

We have: size of   unsigned int a:6+ size of unsigned int b:6 <16 <size of unsigned int a:6+ size of unsigned int b:6 +size of unsigned int c:6
So a and b will be packed together in the space of an integer  (space of 16 bits long),c will be packed alone at a space of 16 bits and d will be packed alone at a space of 16 bits. bit1 is 6 bytes long and it will be :
0000  001110  000101  =  00000011  10000101 =      
0x03  0x85                             
                                                                  (  14=0x0E=b1110)
The low byte is saved first.





     The  C code                                   The result

About structure bit3



struct bitfield3
{

 unsigned int a:5;

unsigned int b:5;

unsigned int c:5;

char d:5;

} bit3; 

 bit3.a=5;

bit3.b=14;

bit3.c=6;

bit3.d=9;

We have: size of unsigned int a:5+ size of unsigned int b:5 +size of unsigned int c:5 <16

So, a  b and c are packed together in a space of 16 bits , bit3 is 4 bytes long and it will be:

 0  00110  01110  00101 = 00011001  11000101 = 0x19  0xc5

bit2 structure is obvius.

Bitfields are useful when memory economy is needed.