2 bits size variable

Question

I need to define a struct which has data members of size 2 bits and 6 bits. Should I use char type for each member?Or ,in order not to waste a memory,can I use

Answer 1

Personally I prefer shift operators and some macros over bit fields, so there's no "magic" left for the compiler. It is usual practice in embedded world.

#define SET_VAL2BIT(_var, _val) ( (_var) | ((_val) & 3) )
#define SET_VAL6BIT(_var, _val) ( (_var) | (((_val) & 63)  << 2) )

#define GET_VAL2BIT(_var) ( (_val) & 3)
#define GET_VAL6BIT(_var) ( ((_var) >> 2) & 63 )

static uint8_t my_var;

<...>
SET_VAL2BIT(my_var, 1);
SET_VAL6BIT(my_var, 5);
int a = GET_VAL2BIT(my_var); /* a == 1 */
int b = GET_VAL6BIT(my_var); /* b == 5 */