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c++cbit-fields

Size of bit field compared to a char

So I know that

struct bit
{
    unsigned char a : 1;
}

will still take up a byte because of padding, my question is this:

struct bit
{
    unsigned char a : 1;
    ...
    unsigned char h : 1;
}

Will this struct take up the same size as a char? And if so, am I better off just using a char instead? I'm asking because I want to use bits as a key, but I'd rather avoid bitwise operations if possible.

Solution

  • There is no guarantees of anything when using bit-fields. That struct can have any size and any bit order. In fact unsigned char type for bit-fields is not even supported by the standard! Your code is already relying on non-standard extensions.

    Forget about bit-fields, forget about char. You should use uint8_t and bitwise operators if you want predictable, portable code.