Question

Suppose I have a byte structure, like this :

struct one_byte
{
char b1 : 1,
     b2 : 1,   
     b3 : 1,   
     b4 : 1,   
     b5 : 1,   
     b6 : 1,   
     b7 : 1,   
     b8 : 1;   
}foo;

In some cases I’ll need to check (foo == 0), then I have to do eight commands :

if(foo.b1 == 0 &&
   foo.b2 == 0 &&
   foo.b3 == 0 &&
...and so on

Is there any portable & convenient way which can instantly check zero value only with a single command? I tried functions & templates, they perform very slowly. And I tried union, my compiler doesn’t support bit[array]….

Answer 1

Use union, this is what it is intended for

union {
  struct {
    char b1:1,b2:1,b3:1,b4:1,b5:1,b6:1,b7:1,b8:1; 
  } bits;
  unsigned char byte;
} u;

then you can either assign directly the byte

u.byte = 15;

or the bits individually

u.bits.b3 = 1;

Exemple

int main() {
  u.byte = 0;
  printf("%x\n", u.byte);
  u.bits.b3 = 1;
  u.bits.b4 = 1;
  printf("%x\n", u.byte);
  return 0;
}

will output

0
c  // 12 in decimal, since b3 and b4 are set to 1