Bit masking

As system, kernel and device driver programmer, you, of course use heavy of bitwise operation. This is a simple C code demonstrate bit masking and it's use in the real world ;), see also bit packing/unpacking for more fun.

#include <stdio.h>

enum {
  SANDRA = 1 << 0,
  DESSY  = 1 << 1,
  YANA   = 1 << 2,
  SUSAN  = 1 << 3
};

void print(unsigned char val)
{
  printf("val: %u\n", val);
  printf("SANDRA loves me: %i\n", (val & SANDRA) ? 1 : 0);
  printf("DESSY loves me: %i\n", (val & DESSY) ? 1 : 0);
  printf("YANA loves me: %i\n", (val & YANA) ? 1 : 0);
  printf("SUSAN loves me: %i\n", (val & SUSAN) ? 1 : 0);
}

int main(void)
{
  unsigned char val = 0;
  val = SANDRA | DESSY | YANA;
  print(val);
  printf("\n");
  val &= ~SANDRA;
  print(val);
  printf("\n");
  val &= ~(DESSY | YANA);
  val |= (SUSAN | SANDRA);
  print(val);
  printf("\n");
  val &= ~(SANDRA | DESSY | YANA | SUSAN);
  print(val);
  return 0;
}