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 something like :2\ :6 notation?
how can I do that?
Can I define a typedef for 2 or 6 bits type?

Answer 1

You can use something like:

typedef struct {
    unsigned char SixBits:6;
    unsigned char TwoBits:2;
} tEightBits;

and then use:

tEightBits eight;
eight.SixBits = 31;
eight.TwoBits = 3;

But, to be honest, unless you’re having to comply with packed data external to your application, or you’re in a very memory constrained situation, this sort of memory saving is not usually worth it. You’ll find your code is a lot faster if it’s not having to pack and unpack data all the time with bitwise and bitshift operations.

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Also keep in mind that use of any type other than _Bool, signed int or unsigned int is an issue for the implementation. Specifically, unsigned char may not work everywhere.