/*
   Illustrates the concept of 'union'  in C (also supported in C++).
   The same 32 bit can be accessed as a 32-bit integer or 4 bytes or 32 bits.
   Compilation: % gcc -ansi bitbyte.c -o executablefilename
*/

#include <stdio.h>
typedef struct {
   unsigned  b3: 8, b2: 8, b1: 8, b0 : 8;
} word_bytes;

typedef struct {
 unsigned
 b31: 1, b30: 1,
 b29: 1, b28: 1, b27: 1, b26: 1, b25: 1, b24: 1, b23: 1, b22: 1, b21: 1, b20: 1,
 b19: 1, b18: 1, b17: 1, b16: 1, b15: 1, b14: 1, b13: 1, b12: 1, b11: 1, b10: 1,
 b9 : 1, b8 : 1, b7 : 1, b6 : 1, b5 : 1, b4 : 1, b3 : 1, b2 : 1, b1 : 1, b0 : 1;
} word_bits;

typedef union {
   int		i;
   word_bytes	byte;
   word_bits	bit;
} word; /* word is the type name for this union  definition */

main()
{ 
   word w = {0}; /* all 32 bits are initialized to zeroes */

   void bit_print(int);
   w.bit.b8 = 1;	/* assign 1 to 8th bit */
   w.byte.b0 = 'B';	/* assign 'B' to 0th byte */
   printf("w.i = %d\n", w.i);
   bit_print(w.i);
}

void bit_print(int v)
/* print the integer parameter value in binary format */
{
  int intsize = 32, i, mask = 1 << (intsize - 1); /* mask = 100 ... 0 */

  for(i = 1; i <= intsize; ++i) {
    putchar(((v & mask) == 0) ? '0' : '1');
    v <<= 1;  /* left shift v by one position; vacant bit is filled with 0 */
    if ((i % 8) == 0)
 	putchar(' ');
  }
  putchar('\n');
}

/*
Output
======
w.i = 322
00000000 00000000 00000001 01000010 

*/